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nanoBoot.S
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nanoBoot.S
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; MIT License
;
; nanoBoot
;
; Copyright (c) 2016 Rodrigo Torres
;
; Permission is hereby granted, free of charge, to any person obtaining a copy
; of this software and associated documentation files (the "Software"), to deal
; in the Software without restriction, including without limitation the rights
; to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
; copies of the Software, and to permit persons to whom the Software is
; furnished to do so, subject to the following conditions:
;
; The above copyright notice and this permission notice shall be included in all
; copies or substantial portions of the Software.
;
; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
; SOFTWARE.
; Original source for nanoBoot
; Simple HID USB Bootloader for AVR Microcontrollers (ATMEGA16U4/ATMEGA32U4)
; HW assumptions:
; CLK is 16 MHz Crystal and fuses are setup correctly to support it:
;
; Select Clock Source (CKSEL3:CKSEL0) fuses are set to Extenal Crystal, CKSEL=1111 SUT=11
; Divide clock by 8 fuse (CKDIV8) can be set to either 0 or 1
;
; Bootloader starts on reset; Hardware Boot Enable fuse is configured, HWBE=0
; Boot Flash Size is set correctly to 256 words (512 bytes), StartAddress=0x3F00, BOOTSZ=11
; Fuse Settings: (Pro Micro like)
; Device signature = 0x1E9587
; lfuse memory = 0xFF
; hfuse memory = 0xD6
; efuse memory = 0xC7
; Fuse Settings: (Teensy 2.0 like)
; Device signature = 0x1E9587
; lfuse memory = 0x5F
; hfuse memory = 0xDF
; efuse memory = 0xC4
; ==========================================================
; LED SUPPORT START
; Turn LED on while bootloader is active
; NOTE: This feature uses 6 bytes for active high and 8 bytes for active low;
; see "Enable LED" in the "run_bootloader" section for details.
; Uncomment the following line to enable LED feature
; #define LED_ENABLED
; LED Configuration
; Uncomment or add a new LED configuration for your specific board
; Adafruit's Atmega32u4 Breakout Board (Product ID: 296) - Now discontinued
; https://www.adafruit.com/product/296
; -- LED is ON with ATmega32u4 PIN E6 HIGH
; #define LED_BIT 6
; #define LED_CONF DDRE
; #define LED_PORT PORTE
; #define LED_ACTIVE_LEVEL 1
; Teensy 2.0 compatible board
; -- LED is ON with ATmega32u4 PIN D6 HIGH
; #define LED_BIT 6
; #define LED_CONF DDRD
; #define LED_PORT PORTD
; #define LED_ACTIVE_LEVEL 1
; Leonardo/Nano compatible board
; -- LED is ON with ATmega32u4 PIN C7 HIGH
; #define LED_BIT 7
; #define LED_CONF DDRC
; #define LED_PORT PORTC
; #define LED_ACTIVE_LEVEL 1
; Pro Micro compatible board
; -- LED is ON with ATmega32u4 PIN D5 LOW
; #define LED_BIT 5
; #define LED_CONF DDRD
; #define LED_PORT PORTD
; #define LED_ACTIVE_LEVEL 0
; Pro Micro compatible board
; -- LED is ON with ATmega32u4 PIN B3 LOW
; #define LED_BIT 3
; #define LED_CONF DDRB
; #define LED_PORT PORTB
; #define LED_ACTIVE_LEVEL 0
#if defined(LED_ENABLED)
#if !defined(LED_PORT) || !defined(LED_CONF) || !defined(LED_BIT) || !defined(LED_ACTIVE_LEVEL)
#error "If LED feature is enabled, the following need to be defined: LED_BIT, LED_CONF, LED_PORT, LED_ACTIVE_LEVEL"
#else
; Set IO register as output for LED
#define ENABLE_LED_OUTPUT sbi _SFR_IO_ADDR(LED_CONF), LED_BIT
#if LED_ACTIVE_LEVEL == 1
#define TURN_LED_ON sbi _SFR_IO_ADDR(LED_PORT), LED_BIT
#define TURN_LED_OFF cbi _SFR_IO_ADDR(LED_PORT), LED_BIT
#elif LED_ACTIVE_LEVEL == 0
#define TURN_LED_ON cbi _SFR_IO_ADDR(LED_PORT), LED_BIT
#define TURN_LED_OFF sbi _SFR_IO_ADDR(LED_PORT), LED_BIT
#else
#error "LED_ACTIVE_LEVEL needs to be either 1 (active high) or 0 (active low)"
#endif
#endif
#endif
; LED SUPPORT END
; ==========================================================
; SW assumptions:
; The bootloader only "needs" endpoint 0; however, the HID spec requires any HID device to have an
; Interrupt IN endpoint, and the host can decide to poll that endpoint even when the HID report
; descriptor does not actually declare any input reports. Because of this, endpoints 0 and 1 are
; configured (in reversed order). See commit bd1bd68e200485aa16445c9d22dd53bb205ee102 for details.
; Register Assignments:
; R0 = temp
; R1 = temp (traditionally, R1 stores constant 0, but we use it as temp because SPM uses R1:R0)
; R2 = 0 (common constant, use instead of traditional R1)
; R3 = 1 (common constant, number is used constantly in the code)
; R4 = copy of MCUSR (MCU Status Register)
; Y = USB_BASE
; Global Flags:
; T Flag (SREG) = BootLoaderActive
; Global Defines:
#define rZERO r2
#define rONE r3
#define rMCUSR r4
; #define rMagicBootKeyL r26 ; currently not used - XL
; #define rMagicBootKeyH r27 ; currently not used - XH
; To make things easier, we are going to handle all Setup Paquets
; the same way, and store the values coming in to the same registers:
; R18 = bmRequestType
; R19 = bRequest
; R20 = wValueL
; R21 = wValueH
; R22 = wIndexL
; R23 = wIndexH
; R24 = wLengthL
; R25 = wLengthH
#define reg_bmRequestType r18
#define reg_bRequest r19
#define reg_wValueL r20
#define reg_wValueH r21
#define reg_wIndexL r22
#define reg_wIndexH r23
#define reg_wLengthL r24
#define reg_wLengthH r25
;
; To facilitate coding, we will use the Y register to point to the first USB register;
; We can then use LDD / STD (Y+oU....) to address USB registers (USB_BASE + relative offset)
;
#define USB_BASE UHWCON
#define oUHWCON (UHWCON - USB_BASE)
#define oUSBCON (USBCON - USB_BASE)
#define oUSBSTA (USBSTA - USB_BASE)
#define oUSBINT (USBINT - USB_BASE)
#define oUDCON (UDCON - USB_BASE)
#define oUDINT (UDINT - USB_BASE)
#define oUDIEN (UDIEN - USB_BASE)
#define oUDADDR (UDADDR - USB_BASE)
#define oUEINTX (UEINTX - USB_BASE)
#define oUENUM (UENUM - USB_BASE)
#define oUERST (UERST - USB_BASE)
#define oUECONX (UECONX - USB_BASE)
#define oUECFG0X (UECFG0X - USB_BASE)
#define oUECFG1X (UECFG1X - USB_BASE)
#define oUESTA0X (UESTA0X - USB_BASE)
#define oUESTA1X (UESTA1X - USB_BASE)
#define oUEIENX (UEIENX - USB_BASE)
#define oUEDATX (UEDATX - USB_BASE)
#define oUEBCX (UEBCX - USB_BASE)
#define oUEBCLX (UEBCLX - USB_BASE)
#define oUEBCHX (UEBCHX - USB_BASE)
#define oUEINT (UEINT - USB_BASE) ; This register has the bits to identify which endpoint triggered an interrupt
#include <avr/io.h>
#ifndef BOOT_ADDRESS
# error "BOOT_ADDRESS not defined!!"
# define BOOT_ADDRESS 0
#endif
.section .vectors
; We still want the reset vector to jump to "main"
.global reset_vector
reset_vector:
cli ; Possibly unnecessary, maybe do something else?
clr rZERO ; Initialize rZERO (R2 register = zero)
rjmp main ; Jump to main
; We are "hiding" the USB descriptors in the Interrupt Vector Table
; NOTE: The 3 instructions above take 6 bytes total, eating into half (2 bytes)
; of the "External Interrupt Request" vector.
; .long 0 /* External Interrupt Request 0 */
; .long 0 /* External Interrupt Request 1 */
; .long 0 /* External Interrupt Request 2 */
; .long 0 /* External Interrupt Request 3 */
; .long 0 /* Reserved */
; .long 0 /* Reserved */
; .long 0 /* External Interrupt Request 6 */
; .long 0 /* Reserved */
; .long 0 /* Pin Change Interrupt Request 0 */
; We have a total 8.5 LWORDS (8.5*4=34 bytes; see NOTE above) to hide part of
; the USB descriptors. We could just hide the Device Descriptor there, but we
; would waste 18 bytes since the config_descriptor would have to be moved after
; the USB-related ISRs (USB General Interrupt Request and the USB Endpoint
; Interrupt Request); instead, we hide the WHOLE Configuration Descriptor,
; including the config_descriptor, interface_descriptor, hid_descriptor and
; endpoint_descriptor which is:
; 9 + 9 + 9 + 7 = 34 bytes, and just leave the device_descriptor and
; hid_report_descriptor (18 + 21 = 39 bytes) defined after the USB-related ISRs.
; 9 bytes
config_descriptor:
// configuration descriptor, USB spec 9.6.3, page 264-266, Table 9-10
.byte 9 // bLength -- Size of Descriptor in Bytes
.byte 2 // bDescriptorType -- Configuration Descriptor (0x02)
.word 9+9+9+7 // wTotalLength -- Total length in bytes of data returned -> ; this is for the whole configuration (4 descriptors)
.byte 1 // bNumInterfaces -- Number of Interfaces
.byte 1 // bConfigurationValue -- Value to use as an argument to select this configuration
.byte 0 // iConfiguration -- Index of String Descriptor describing this configuration
.byte 0x80 // bmAttributes -- D7 Reserved (set to 1), D6 Self Powered, D5 Remote Wakeup, D4..D0 Reserved (set to 0)
.byte 50 // bMaxPower -- Maximum Power Consumption in 2mA units (50 = 100mA)
; 9 bytes
interface_descriptor:
// interface descriptor, USB spec 9.6.5, page 267-269, Table 9-12
.byte 9 // bLength -- Size of Descriptor in Bytes (9 Bytes)
.byte 4 // bDescriptorType -- Interface Descriptor (0x04)
.byte 0 // bInterfaceNumber -- Number of Interface
.byte 0 // bAlternateSetting -- Value used to select alternative setting
.byte 1 // bNumEndpoints -- Number of Endpoints used for this interface
.byte 0x03 // bInterfaceClass -- Class Code (0x03 = HID class | 0xFF = Vendor Specific)
.byte 0x00 // bInterfaceSubClass -- Subclass Code
.byte 0x00 // bInterfaceProtocol -- Protocol Code
.byte 0 // iInterface -- Index of String Descriptor Describing this interface
; 9 bytes
hid_descriptor:
.byte 9 // bLength -- Size of Descriptor in Bytes (9 Bytes)
.byte 0x21 // bDescriptorType -- HID Descriptor (0x21)
.word 0x0111 // bcdHID -- HID specification release number (BCD) (1.1)
.byte 0 // bCountryCode -- Numeric expression identifying the country for localized hardware
.byte 1 // bNumDescriptors -- Number of Report Descriptors
.byte 0x22 // bDescriptorType -- The type of a class-specific descriptor that follows (Report Descriptor = 0x22)
.word 21 // wDescriptorLength -- Total length of the descriptor identified above (length of Report Descriptor = 21 bytes)
; 7 bytes
endpoint_descriptor:
.byte 7 // bLength -- Size of Descriptor in Bytes (7 Bytes)
.byte 0x05 // bDescriptorType -- Enpoint Descriptor (0x05)
.byte 0x81 // bEndpointAddress -- Endpoint number and direction (0x80 Input | 0x01 Address)
.byte 0x03 // bmAttributes -- Transfer type = interrupt
.word 64 // wMaxPacketSize -- Maximum packet size supported in bytes (64)
.byte 5 // bInterval -- Polling interval (milliseconds)
; USB-related ISRs are here!!!
.org reset_vector + 0x28
.global USB_General_Vector
USB_General_Vector:
; The following is an optimization by "osamuaoki" that saves 2 bytes.
; It uses the full space (4 bytes) of the USB_General_Vector to store an
; instruction (std) that used to be part of the USB_General_ISR, which
; gets called from here anyway; so it makes sense to pack it here. This
; can only be done because the following assumption is valid:
; ASSUMPTION!
; We know we ONLY enable End Of Reset Interrupt (EORSTE) during USB
; Initialization, so we don't need to check that; basically, if we enter
; this interrupt (USB General) it's because we need to service the End Of
; Reset Interrupt (EORSTI).
; This following line will be necessary if the assumption above ever
; changes, since we would need to filter invidual interrupt sources
; ldd r17, Y+oUDINT ; Load r17 with the value in the USB Device Interrupt Flag Register (UDINT), create a copy of the interrupt flags
; Given the assumption above, we can simply clear the whole USB Device Interrupt Flag Register (UDINT) to acknowledge the interrupt
std Y+oUDINT, rZERO ; Load the USB Device Interrupt Flag Register (UDINT) with zero (clear all USB-related interrupts)
; If we ever need to distinguish among multiple interrupt sources, we can filter them using code like the following
; sbrs r17, EORSTI ; Skip the next instruction if the End Of Reset Interrupt Flag (EORSTI) is set;
; Don't jump if “End Of Reset” has been detected by the USB controller; thus service the End Of Reset interrupt
; rjmp not_EORSTI
; IMPORTANT NOTE: If the code above ever changes (grows), it will need to
; be moved back to the USB_General_ISR section, since interrupt vectors
; only allocate 4 bytes, basically enough space to jump to actual ISR.
rjmp USB_General_ISR /* USB General Interrupt Request */
.org reset_vector + 0x2c
.global USB_Endpoint_Vector
USB_Endpoint_Vector:
rjmp USB_Endpoint_ISR /* USB Endpoint/Pipe Interrupt Communication Request */
; 18 bytes
device_descriptor:
.byte 18 // bLength -- Size of the Descriptor in Bytes (18 bytes)
.byte 1 // bDescriptorType -- Device Descriptor (0x01)
.word 0x0110 // bcdUSB -- USB Specification Number which device complies to
.byte 0 // bDeviceClass -- Class Code
.byte 0 // bDeviceSubClass -- Subclass Code
.byte 0 // bDeviceProtocol -- Protocol Code
.byte 64 // bMaxPacketSize0 -- Maximum Packet Size for Zero Endpoint (64 bytes)
.word 0x03EB // idVendor -- Vendor ID (Atmel VID, from LUFA)
.word 0x2067 // idProduct -- Product ID (HID Class Bootloader PID, from LUFA)
.word 0x0001 // bcdDevice -- Device Release Number
.byte 0 // iManufacturer -- Index of Manufacturer String Descriptor
.byte 0 // iProduct -- Index of Product String Descriptor
.byte 0 // iSerialNumber -- Index of Serial Number String Descriptor
.byte 1 // bNumConfigurations -- Number of Possible Configuration
; 21 bytes
hid_report_descriptor:
.byte 0x06, 0xDC, 0xFF // Usage Page (Vendor Defined 0xDCFF)
.byte 0x09, 0xFB // Usage (0xFB)
.byte 0xA1, 0x01 // Collection (Application)
.byte 0x09, 0x02 // Usage (0x02)
.byte 0x15, 0x00 // Logical Minimum (0)
.byte 0x25, 0xFF // Logical Maximum (255)
.byte 0x75, 0x08 // Report Size (8)
.byte 0x96, 0x82, 0x00 // Report Count (130) -> SPM_PAGESIZE (128 bytes) + 2
.byte 0x91, 0x02 // Output (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position,Non-volatile)
.byte 0xC0 // End Collection
; =================================================================
; == Entry point!
; =================================================================
.section .text
.global main
; =================================================================
; = Check if bootloader/application should execute
; Watchdog Timer Reset
; TODO: Add magic word check?
; =================================================================
main:
; =================================================================
; = Initialize constants
; =================================================================
; Set R3=rONE
clr rONE ; Initialize rONE as 0 (application may have set this before RESET)
inc rONE ; Initialize rONE (R3 register = one)
; Create a copy of the MCUSR (MCU Status Register) as soon as possible
in rMCUSR, _SFR_IO_ADDR(MCUSR) ; Load MCU Status Register to rMCUSR
out _SFR_IO_ADDR(MCUSR), rZERO ; Load MCU Status Register with rZERO (clear reset flags, particularly clear WDRF in MCUSR), necessary before disabling the Watchdog
; We MUST disable the Watchdog Timer first, otherwise it will remain enabled and will keep resetting the system, so...
; Disable Watchdog Timer
mov r17, rZERO ; Load r17 with zero to disable the Watchdog Timer completely
rcall set_watchdog_timer ; Call the subroutine that sets the watchdog timer with the value loaded in r17
; check_reset_flags:
sbrs rMCUSR, EXTRF ; Skip the next instruction if EXTRF is set (if External Reset Flag, skip next instruction, go to run_bootloader)
run_application: ; We get here if the cause of the reset was anything but an Extenal Reset (push-button)
jmp 0 ; Simply jump to 0x0000 (application) IMPORTANT NOTE!! This CANNOT be an 'rjmp'!!
run_bootloader:
set ; Initialize BootLoaderActive flag (T flag in SREG)
; Enable LED
#if defined(LED_ENABLED)
; Set IO register as output for LED
ENABLE_LED_OUTPUT
; If the LED is active low, we need to turn it off here (set LED_BIT) since the MCU IO port is
; initialized as 0. This is a 2-byte penalty when using active low LED.
#if LED_ACTIVE_LEVEL == 0
TURN_LED_OFF
#endif
#endif
; =================================================================
; = Setup IRQ Vector Table
; =================================================================
; Move the IRQ Vector Table to the beginning of the Boot Flash Space
; ONLY if the BOOT_ADDRESS is not zero!
#if (BOOT_ADDRESS != 0)
ldi r17, _BV(IVSEL) ; Load r17 with the value needed to set the Interrupt Vectors to the beginning of the Boot Loader section of the Flash
; Set a logic one to the Interrupt Vector Select bit (IVSEL); for this to work, the Vector Change Enable bit (IVCE) MUST be set to logic zero!
; Set a logic one to the Interrupt Vector Change Enable bit (IVCE)
out _SFR_IO_ADDR(MCUCR), rONE ; Store MCU Control Register (MCUCR) with the value needed to "unlock" the Interrupt Vector Change Configuration
out _SFR_IO_ADDR(MCUCR), r17 ; Store r17 to the MCU Control Register (MCUCR)
#endif
; =================================================================
; = Setup Stack
; = UNNECESARY SINCE ATMEGA32U4 DOES THIS AUTOMATICALLY!
; =================================================================
; Set up the stack (TODO: is this necessary?), we won't be using the stack anyway
; ldi r16, hi8(RAMEND) ; Load r16 with the most significant 8 bits of RAMEND
; ldi r17, lo8(RAMEND) ; Load r17 with the least significant 8 bits of RAMEND
; out _SFR_IO_ADDR(SPH), r16 ; Set the Stack Pointer High byte (SPH) with the value in r16
; out _SFR_IO_ADDR(SPL), r17 ; Set the Stack Pointer Low byte (SPL) with the value in r17
; =================================================================
; = Setup System Clock (16 MHz XTAL)
; = UNNECESARY SINCE FUSES TAKE CARE OF THIS!!
; =================================================================
; lds r16, CLKSEL0 ; Load the value of Clock Selection Register 0 (CLKSEL0) to r16
; ori r16, _BV(EXTE) | _BV(CLKS) ; Set Enable External Clock (EXTE) and Clock Selector (CLKS) bits in the value loaded in r16
; sts CLKSEL0, r16 ; Store r16 to the Clock Selection Register 0 (CLKSEL0)
; 1: lds r17, CLKSTA ; Load the value of Clock Status Register (CLKSTA) to r17
; sbrs r17, EXTON ; Skip the next instruction if the External Clock On bit (EXTON) is set (External Clk is running); basically, move on
; rjmp 1b ; Jump to 1Backwards if the External Clock On bit (EXTON) is not set (External Clk not running)
; The following is a functional improvement by "osamuaoki", after he was
; able to free up enough space to fit this in. Basically, this allows the
; "Divide clock by 8" fuse (CKDIV8) to be set to any value (0 or 1), since
; we are setting the clock prescaler to zero here, effectively setting the
; System Clock to 16 MHz, which is one of the HW assumptions made for the
; code to work as expected.
ldi r17, _BV(CLKPCE) ; Load r17 with the value needed to "unlock" the prescaler of the Clock; Clock Prescaler Change Enable bit (CLKPCE) set to one, all other bits set to zero.
sts CLKPR, r17 ; Store r17 to the Clock Prescaler Register (CLKPR)
sts CLKPR, rZERO ; Store rZERO to the Clock Prescaler Register (CLKPR), setting CLKPS3, CLKPS2, CLKPS1 and CLKPS0 to zero (Clock Division Factor = 1; System Clock is 16 MHz)
; =================================================================
; = Basic device setup is NOW COMPLETE!!
; =================================================================
; =================================================================
; = USB Initialization
; = Configure Y register to point to USB_BASE (UHWCON register)
; =================================================================
ldi YL, lo8(USB_BASE) ; Load YL with the least significant 8 bits of USB_BASE
ldi YH, hi8(USB_BASE) ; Load YH with the most significant 8 bits of USB_BASE
; =================================================================
; = From LUFA simplified - USB_Init:_start
; =================================================================
; Reset USB Interface
; The reset value of the USB Controller Register (USBCON) is USBE = 0, FRZCLK = 1, OTGPADE = 0, VBUSTE = 0
; The following is a workaround for AVR8 bootloaders that fail to turn off the OTG pad before
; running the loaded application. This causes VBUS detection to fail unless we first force it
; off to reset it.
; Force disable VBUS Pad (OTGPADE), also disable all USB-related Interrupts (VBUSTE) and reset the USB controller (USBE)
; USBCON &= ~(1 << OTGPADE);
; USBCON &= ~(1 << VBUSTE);
; USBCON &= ~(1 << USBE);
; IMPORTANT NOTE: To reduce code size, we are going to reseve r16 to handle all writes to the USB Controller Register (USBCON)
; this way we don't have to keep loading the value to it (ldd)
ldd r16, Y+oUSBCON ; Load r16 with the value in the USB Configuration Register (USBCON)
; The right value of USBCON is already in r16, just clear VBUS Pad Enable Bit (OTGPADE),
; VBUS Transition Interrupt Enable Bit (VBUSTE) and USB macro Enable Bit (USBE)
andi r16, ~(_BV(OTGPADE)|_BV(VBUSTE)|_BV(USBE))
std Y+oUSBCON, r16 ; Store r16 to the USB Configuration Register (USBCON)
; Enable USB Regulator (USB_REG_On)
; UHWCON |= (1 << UVREGE);
; Set a logic one to the USB pad regulator bit (UVREGE)
std Y+oUHWCON, rONE ; Store USB Hardware Configuration Register (UHWCON) with the value needed to enable the USB pad regulator
; SIZE OPTIMIZATION: Not needed due to known reset value (Zero)
; ; Disable all USB Device-related Interrupts
; ; UDIEN = 0;
; std Y+oUDIEN, rZERO ; Load the USB Device Interrupt Enable Register (UDIEN) with zero (disable all USB Device-related interrupts)
; SIZE OPTIMIZATION: Not needed due to known reset value (Zero)
; ; Clear all USB-related Interrupts
; ; USBINT = 0;
; ; UDINT = 0;
; std Y+oUSBINT, rZERO ; Load the USB General Interrupt Flag Register (USBINT) with zero (clear the IVBUS Transition Interrupt Flag (VBUSTI))
; std Y+oUDINT, rZERO ; Load the USB Device Interrupt Flag Register (UDINT) with zero (clear all USB Device-related interrupts)
; Enable the USB Controller
; USBCON |= (1 << USBE);
ori r16, _BV(USBE) ; The right value of USBCON is already in r16, just set the USB macro Enable Bit (USBE)
std Y+oUSBCON, r16 ; Store r16 to the USB Configuration Register (USBCON)
; Set PLL Output Frequency to 48MHz
; PLLFRQ = (1 << PDIV2);
ldi r17, _BV(PDIV2) ; Load r17 with the value needed to set the PLL Lock Frequency to 48MHz (only PDIV2 bit set to 1)
; The PLL Input Multiplexer (PMUX) bit is set to 0 because the PLL input is connected to the PLL Prescaler, which has the Primary System Clock as source
; The PLL Postcaler for USB Peripheral (PLLUSB) is set to 0 because we don't need further division (PDIV2 set to 1 -> PLL Output = 48MHz)
out _SFR_IO_ADDR(PLLFRQ), r17 ; Store r17 to the PLL Frequency Control Register (PLLFRQ)
; Unfreeze USB Clk
; USBCON &= ~(1 << FRZCLK);
andi r16, ~(_BV(FRZCLK)) ; The right value of USBCON is already in r16, just clear the Freeze Clock bit (FRZCLK)
std Y+oUSBCON, r16 ; Store r16 to the USB Configuration Register (USBCON)
; Enable USB PLL (USB_PLL_On)
; PLLCSR = (1 << PINDIV);
; PLLCSR = ((1 << PINDIV) | (1 << PLLE));
ldi r17, _BV(PINDIV) ; Load r17 with the value needed to set the PLL input prescaler to generate the 8MHz input clock for the PLL
; When using a 16MHz clock source, PINDIV PLL Input Prescaler (PINDIV) bit must be set to 1 before enabling PLL
out _SFR_IO_ADDR(PLLCSR), r17 ; Store r17 to the PLL Control and Status Register (PLLCSR)
ldi r17, (_BV(PINDIV) | _BV(PLLE)); Load r17 with the value needed to enable the PLL, set PLL Enable bit (PLLE), we are also setting PINDIV to keep the PLL input prescaler configuration
out _SFR_IO_ADDR(PLLCSR), r17 ; Store r17 to the PLL Control and Status Register (PLLCSR)
; Wait for PLL Lock Detector to assert
; while (!(USB_PLL_IsReady()));
wait_pll_lock:
in r17, _SFR_IO_ADDR(PLLCSR) ; Load r17 with the value of the PLL Control and Status Register (PLLCSR)
sbrs r17, PLOCK ; Skip the next instruction if the PLL Lock Detector bit (PLOCK) is set (PLL is locked to the reference clock)
rjmp wait_pll_lock ; Loop while PLOCK is not set
; Enable ONLY "End Of Reset Interrupt"
; UDIEN |= (1 << EORSTE);
; NOTE: We are not ORing the value of UDIEN, because we really just want EORSTE enabled
ldi r17, _BV(EORSTE) ; Load r17 with the value needed to enable the USB-related interrupts we care about, EORSTE
std Y+oUDIEN, r17 ; Store r17 to the USB Interrupt Enable Register (UDIEN)
; Attach device to USB Bus and select USB Full speed mode (also clears USB reset CPU bit <RSTCPU> and remote wake-up bit <RMWKUP>)
; IMPORTANT!! The reset value of UDCON is not 0x00, it's 0x01 (DETACH bit = 1), so we MUST write ZERO to it here!!
; UDCON = 0;
std Y+oUDCON, rZERO ; Store rZERO to the USB Device Configuration Register (UDCON); clear Detach Bit (DETACH);
; This reconnects the device, and sets FULL SPEED Mode, LSM bit set to 0 (D+ internal pull-up)
; Enable VBUS Pad (USB_OTGPAD_On), while keeping USB macro Enable bit set
; USBCON |= (1 << OTGPADE);
ldi r16, (_BV(USBE)|_BV(OTGPADE)) ; Load r16 with the value needed to enable the USB controller, enable clock;
; USB macro Enable Bit (USBE) is set to 1 (enable the USB controller)
; Freeze Clock bit (FRZCLK) set to 0 (enable the clock inputs)
; VBUS Pad Enable bit (OTGPADE) set to 1 (enable the VBUS pad)
; VBUS Transition Interrupt Enable Bit (VBUSTE) set to 0 (disable the VBUS Transition interrupt generation)
std Y+oUSBCON, r16 ; Store r16 to the USB Configuration Register (USBCON)
; =================================================================
; = From LUFA simplified - USB_Init:_end
; =================================================================
; =================================================================
; = USB Initialization is NOW COMPLETE!!
; =================================================================
sei ; Set Global Interrupt Flag (Enable system interrupts)
; =================================================================
; = USB is running, interrupts enabled!!
; =================================================================
; =================================================================
; = Main Bootloader Loop
; =================================================================
main_loop:
brts main_loop ; Loop while the T (BootLoaderActive) flag in SREG is set
exit_bootloader:
; Detach device from USB Bus
; UDCON |= (1 << DETACH);
ldd r16, Y+oUDCON ; Load r16 with the value in the USB Device Configuration Register (UDCON)
ori r16, _BV(DETACH) ; Set the DETACH bit to enable the detachment
std Y+oUDCON, r16 ; Store r16 to the USB Device Configuration Register (UDCON)
#if defined(LED_ENABLED)
; Turn LED off before exiting
TURN_LED_OFF
#endif
; =================================================================
; = Watchdog Timer initialization
; =================================================================
; NOTE!! This part of the code assumes MCUSR has already been cleared
; Enable WDT, ~250 ms timeout (force a timeout to reset the AVR)
ldi r17, _BV(WDE) | _BV(WDP2) ; Load r17 with the value needed to set the desired Watchdog Configuration (WDCE = 0, not set!)
; Write the WDE and Watchdog prescaler bits (WDP); System Reset Mode (WDE = 1) and ~250 ms timeout (WDP2 = 1)
rcall set_watchdog_timer ; Call the subroutine that sets the watchdog timer with the value loaded in r17
; for (;;);
final_loop:
rjmp final_loop ; keep looping here until the Watchdog timer kicks in,
; this will reset the MCU the new app should run
; =================================================================
; = USB General ISR
; =================================================================
; This just watches for EORSTI (End of Reset Interrupt) and enables
; Endpoint 0.
.global USB_General_ISR
USB_General_ISR:
; WARNING: REGISTERS/CONTEXT NOT SAVED!
; service_EORSTI: ; unused label
; =================================================================
; = Configure Endpoints
; =================================================================
; Even though the bootloader uses only endpoint 0, the HID spec requires any HID device to have an
; Interrupt IN endpoint, and the host can decide to poll that endpoint even when the HID report
; descriptor does not actually declare any input reports. Polling an unconfigured endpoint causes
; USB errors, therefore endpoint 1 must be configured here too.
; Enable and configure endpoint 1 as Interrupt IN:
; UENUM = 1;
; UECONX |= (1 << EPEN);
; UECFG0X = (1 << EPTYPE1) | (1 << EPTYPE0) | (1 << EPDIR);
; UECFG1X = (1 << EPSIZE1) | (1 << EPSIZE0) | (1 << ALLOC);
std Y+oUENUM, rONE ; Select Endpoint 1
; Set Endpoint Enable Bit (EPEN), all other bits set to zero has no effect on UECONX
std Y+oUECONX, rONE ; Store the USB Endpoint Configuration Register (UECONX) with the value needed to enable Endpoint 1
ldi r16, (_BV(EPTYPE1) | _BV(EPTYPE0) | _BV(EPDIR)) ; Load r16 with the value to configure Endpoint 1
; Endpoint Type Bits (EPTYPE1:0); 11 to set as Interrupt Endpoint
; Endpoint Direction Bit (EPDIR); set to configure IN direction
std Y+oUECFG0X, r16 ; Store r16 to the USB Endpoint Configuration0 Register (UECFG0X);
ldi r16, (_BV(EPSIZE1) | _BV(EPSIZE0) | _BV(ALLOC)) ; Load r16 with the value to configure Endpoint 1 (and also 0 below)
; Endpoint Size Bits (EPSIZE2:0); 011 to set to 64 bytes
; Endpoint Bank Bits (EPBK1:0); 00 to set One bank
; Endpoint Allocation Bit (ALLOC); set to allocate the endpoint memory
std Y+oUECFG1X, r16 ; Store r16 to the USB Endpoint Configuration1 Register (UECFG1X);
; Enable and configure endpoint 0 as Control (this is done last, so that endpoint 0 will remain selected):
; UENUM = 0;
; UECONX |= (1 << EPEN);
; UECFG0X = 0;
; UECFG1X = (1 << EPSIZE1) | (1 << EPSIZE0) | (1 << ALLOC);
std Y+oUENUM, rZERO ; Select Endpoint0
; Set Endpoint Enable Bit (EPEN), all other bits set to zero has no effect on UECONX
std Y+oUECONX, rONE ; Store the USB Endpoint Configuration Register (UECONX) with the value needed to enable Endpoint 0
; SIZE OPTIMIZATION: Not needed due to known reset value (Zero)
; std Y+oUECFG0X, rZERO ; Store rZERO to the USB Endpoint Configuration0 Register (UECFG0X);
; Endpoint Type Bits (EPTYPE1:0): 00 to set as Control Endpoint
; Endpoint Direction Bit (EPDIR): clear to configure OUT direction; needed for Control Endpoint
; SIZE OPTIMIZATION: r16 is already loaded with the required value while configuring endpoint 1 above
std Y+oUECFG1X, r16 ; Store r16 to the USB Endpoint Configuration1 Register (UECFG1X);
; Enable "Received SETUP Interrupt"
; UEIENX |= (1 << RXSTPE);
ldi r16, _BV(RXSTPE) ; Load r16 with the value to needed to enable an endpoint interrupt (EPINTx) when RXSTPI is sent.
; Received SETUP Interrupt Enable Bit (RXSTPE) set to 1
std Y+oUEIENX, r16 ; Store r16 to the USB Endpoint Interrupt Enable Register (UEIENX);
not_EORSTI:
reti ; Return from interrupt
; =================================================================
; = USB Endpoint Interrupt
; =================================================================
; ASSUMPTION!!!
; Since only EP0 is ever enabled, this should be for that endpoint.
; If some other EP interrupts, we don't handle it.
; Also, since we only enable RXSTPE, this must be to handle RXSTPI
.global USB_Endpoint_ISR
USB_Endpoint_ISR:
; =================================================================
; = Process USB Control Request
; =================================================================
; Get the 8-byte setup packet
; The following code is a slightly shorter version of:
; ldd reg_bmRequestType, Y+oUEDATX ; bmRequestType
; ldd reg_bRequest, Y+oUEDATX ; bRequest
; ldd reg_wValueL, Y+oUEDATX ; wValueL
; ldd reg_wValueH, Y+oUEDATX ; wValueH
; ldd reg_wIndexL, Y+oUEDATX ; wIndexL
; ldd reg_wIndexH, Y+oUEDATX ; wIndexH
; ldd reg_wLengthL, Y+oUEDATX ; wLengthL
; ldd reg_wLengthH, Y+oUEDATX ; wLengthH
; Shorter version
clr XH ; Clear XH Register
ldi XL, 18 ; Load XL Register with number 18 (this will be used to refer to r18)
load: ldd r0, Y+oUEDATX ; Load r0 with the value in the USB Endpoint Data Register (UEDATX)
st X+, r0 ; Store the value of r0 to the location pointed by X (r18), post increment X (X now points to r19)
cpi XL, 18+8 ; Compare XL with the location past the last byte that we need to read
brne load ; Jump back to 'load' if there are still bytes to read
; Our response is based on data direction...
sbrc reg_bmRequestType, 7 ; Skip the next instruction if bit 7 of bmRequestType is not set; for host to device (OUT) transaction, bit 7 is cleared
rjmp DEVICE_TO_HOST ; If bit 7 of bmRequestType is set, this is a device to host (IN) transaction, jump to DEVICE_TO_HOST
; OUT transactions
HOST_TO_DEVICE:
; For OUT transactions, here we ONLY handle standard requests targeted for the device
cpi reg_bmRequestType, 0x00 ; Compare r18 (bmRequestType) with value 0x00 (OUT Type Resquest, USB Standard Request, Recipient is the device)
breq HANDLE_USB_STANDARD_DEVICE ; If bmRequestType is 0x00, we know it's either a SET_ADDRESS or SET_CONFIGURATION request, so jump to HANDLE_USB_STANDARD_DEVICE
andi reg_bmRequestType, (0x60 | 0x1F) ; Mask reg_bmRequestType with the bits that define request type and recipient (CONTROL_REQTYPE_TYPE | CONTROL_REQTYPE_RECIPIENT)
cpi reg_bmRequestType, ((1 << 5) | (1 << 0)) ; Compare the masked value in r16 with the value that defines the request type and recipient we care about HID_SET_REPORT (REQTYPE_CLASS | REQREC_INTERFACE)
brne UNHANDLED_SETUP_REQUEST_1 ; jump to UNHANDLED_SETUP_REQUEST through a thunk if not equal
; fallthrough to HANDLE_USB_CLASS_INTERFACE if equal
HANDLE_USB_CLASS_INTERFACE:
cpi reg_bRequest, 0x09 ; Compare bRequest with value 0x05 (HID_REQ_SetReport)
breq SET_HID_REPORT ; jump to SET_HID_REPORT
rjmp UNHANDLED_SETUP_REQUEST ; If reg_bmRequestType is not 0x00 or bRequest is not 0x05 or 0x09, we don't handle those cases, so jump to UNHANDLED_SETUP_REQUEST
HANDLE_USB_STANDARD_DEVICE:
; Once we know we support the OUT transaction, we need to filter it based on the value in bRequest
cpi reg_bRequest, 0x05 ; Compare bRequest with value 0x05 (REQ_SetAddress)
breq SET_ADDRESS ; jump to SET_ADDRESS
cpi reg_bRequest, 0x09 ; Compare bRequest with value 0x09 (REQ_SetConfiguration)
brne UNHANDLED_SETUP_REQUEST_1 ; jump to UNHANDLED_SETUP_REQUEST through a thunk if not equal
; fallthrough to SET_CONFIGURATION if equal
SET_CONFIGURATION:
#if defined(LED_ENABLED)
; Turn LED on towards the end of enumeration (SET_CONFIGURATION is done after SET_ADDRESS)
; TODO: If we ever have space, we could add a flag here to mark the fact that we have entered
; this state, and turn the LED on at the end of the setup request. For now this is the best we
; can do.
TURN_LED_ON
#endif
; Optimization by "sigprof" that saves 2 bytes
; Dirty trick: We don't need to do anything for SET_CONFIGURATION except process_Host2Device,
; so we reuse the SET_ADDRESS code by making it reload the same value to UDADDR.
ldd reg_wValueL, Y+oUDADDR ; load the existing UDADDR value where the SET_ADDRESS code would expect the new address
SET_ADDRESS:
; Set device address; for this we only need to copy the value in wValueL which contains the address
; for the device set by the host to the USB Device Address Register (UDADDR); since the SET_ADDRESS
; request is only executed once during enumeration, and because allowed address values are 1 through
; 127 (7 LSBs), we don't need to care about the ADDEN bit (bit 7). We can also simply set the ADDEN
; bit and store the value again in UDADDR to enable the USB Device Address.
std Y+oUDADDR, reg_wValueL ; Store wValueL to the USB Device Address Register (UDADDR)
rcall process_Host2Device ; This function affects r17
; EnableDeviceAddress
; UDADDR |= (1 << ADDEN)
ori reg_wValueL, _BV(ADDEN) ; In order to save space, we simply OR the address value already in reg_wValueL (r20) with the ADDEN bit to enable the USB Address
std Y+oUDADDR, reg_wValueL ; Store reg_wValueL to the USB Device Address Register (UDADDR)
UNHANDLED_SETUP_REQUEST_1:
rjmp UNHANDLED_SETUP_REQUEST ; Go to UNHANDLED_SETUP_REQUEST
SET_HID_REPORT:
; Acknowledge the SETUP packet
rcall clear_RXSTPI ; This function uses r17 to clear the RXSTPI bit in UEINTX
; Wait for command from the host
rcall wait_RXOUTI ; This function loads r17 with value of UEINTX
load_page_address:
ldd r30, Y+oUEDATX ; Load r30 with LSB of page address
ldd r31, Y+oUEDATX ; Load r31 with MSB of page address
check_page_address:
; Protect against overwriting the bootloader - allow flash write only if the specified address is
; less than the bootloader start address. Only the high byte needs to be tested, because the
; bootloader start is guaranteed to be on a 256 bytes boundary.
cpi r31, hi8(reset_vector) ; Compare high byte of page address against the high byte of the bootloader start addresss
brcs erase_page ; If the address is below the bootloader start, allow the flash write operation
; The address is definitely not correct for a flash write operation; however, simply jumping to
; finish_hid_request would not just fail this SET_HID_REPORT request - apparently not reading the
; OUT data properly results in the bootloader not responding to any subsequent USB requests too.
; Instead of doing that, we run the normal flash write loop even if the address was bad, but set
; the "disable flash write" bit, so that the actual flash write instructions will be skipped.
; Bit 7 of reg_bRequest is used for that purpose - is is known to be 0 in the normal case.
sbr reg_bRequest, _BV(7) ; Set the "disable flash write" bit
; If the address is out of the allowed range for flash write, it may be the special value for the
; START_APPLICATION command (0xffff); check for that value in the shortest way possible.
adiw r30, 1 ; Increment the address to turn 0xffff into 0x0000
brne erase_page ; If the address was out of range and not 0xffff, jump to the regular flash write code
; (which would just consume the OUT data to make USB work properly).
clt ; Otherwise (the address was 0xffff) clear the BootLoaderActive flag (T flag in SREG),
; then fallthrough to the regular flash write code too.
erase_page:
ldi r17, (_BV(PGERS)|_BV(SPMEN)) ; load r17 with the value needed to erase the currently specified page
rcall do_SPM ; execute page erase (this function requires r17 to be loaded first with the right value for SPMCSR)
clear_current_page_byte_address:
ldi r16, (SPM_PAGESIZE/2) ; load r16 with the number of words per page (128 bytes/2 = 64 words)
; r16 will be decremented for every word (2 bytes) we write to the page buffer
check_endpoint_for_more_data:
; if (!(((uint16_t)UEBCHX << 8) | UEBCLX))
; we just check for UEBCLX, we know we can't accept more than 130 bytes at a time (hid_report_descriptor)
; ldd r27, Y+oUEBCHX ; load r27 with the value of USB Endpoint Byte Count High Register (UEBCHX)
ldd r26, Y+oUEBCLX ; load r26 with the value of USB Endpoint Byte Count Low Register (UEBCLX)
; or r27, r27
or r26, r26
brne fill_page_buffer ; if r26 is not zero, it means there's data in the endpoint which we can use to fill the page buffer, jump there
; Acknowledge the OUT packet
rcall clear_RXOUTI ; This function uses r17 to clear the RXOUTI bit in UEINTX
; Wait for more data from the host
rcall wait_RXOUTI ; This function loads r17 with value of UEINTX
fill_page_buffer: ; There's data at the endpoint buffer, start fill_page_buffer sequence
load_word_data:
ldd r0, Y+oUEDATX ; Load r0 with LSB of data word
ldd r1, Y+oUEDATX ; Load r1 with MSB of data word
write_page_buffer:
ldi r17, _BV(SPMEN) ; load r17 with the value needed to write the current word to the page buffer
rcall do_SPM ; execute page buffer write (this function requires r17 to be loaded first with the right value for SPMCSR)
increment_byte_address:
subi r30, -2 ; Increment the current address by 2.
; Only the low byte needs to be incremented, because the block start address must be page aligned,
; therefore any carry to the high byte may happen only past the end of the block.
dec r16 ; decrement r16 (number of words per page)
brne check_endpoint_for_more_data ; loop while r16 is not equal to SPM_PAGESIZE (128)
; Restore the page address in Z-Register
subi r30, SPM_PAGESIZE ; Move the address back to the start of page (again only the low byte needs to be changed).
write_page_to_flash:
ldi r17, (_BV(PGWRT)|_BV(SPMEN)) ; load r17 with the value needed to commit the current page buffer to the flash
rcall do_SPM ; execute page write to flash (this function requires r17 to be loaded first with the right value for SPMCSR)
reenable_rww_section:
ldi r17, (_BV(RWWSRE)|_BV(SPMEN)) ; load r17 with the value needed to reebable the rww section
rcall do_SPM ; execute re-enable rww section (this function requires r17 to be loaded first with the right value for SPMCSR)
finish_hid_request:
; Acknowledge the OUT packet
rcall clear_RXOUTI ; This function uses r17 to clear the RXOUTI bit in UEINTX
; Wait for TXINI (OK to transmit)
rcall wait_TXINI ; This function loads r17 with value of UEINTX
; Clear Transmitter Ready Flag
rcall clear_TXINI ; This function uses r17 to clear the TXINI bit in UEINTX
UNHANDLED_DEVICE_TO_HOST:
rjmp UNHANDLED_SETUP_REQUEST ; Go to UNHANDLED_SETUP_REQUEST
; IN transactions
DEVICE_TO_HOST:
; If we get here, we know bit 7 of bmRequestType is set, meaning it is a DEVICE_TO_HOST (IN) request,
; now we need to filter out any unhandled requests
cbr reg_bmRequestType, 0x01 ; We mask reg_bmRequestType with value 0x01, bit 0 of bmRequestType is set if the recipient of the request is the interface,
; and we need to handle that case since the host will query the interface to retrieve the hid_descriptor, obviously we also
; need to handle the recipient being the device (bit 0 = 0) since all other descriptors are targeted to it
cpi reg_bmRequestType, 0x80 ; Compare r18 (bmRequestType) with value 0x80 (IN Type Resquest, USB Standard Request, Recipient is the device/interface)
brne UNHANDLED_DEVICE_TO_HOST ; If bmRequestType is not 0x80, we know it's not a GET_DESCRIPTOR request, so jump to UNHANDLED_DEVICE_TO_HOST
cpi reg_bRequest, 0x06 ; Compare bRequest with value 0x06 (REQ_GetDescriptor)
brne UNHANDLED_DEVICE_TO_HOST ; jump to UNHANDLED_SETUP_REQUEST through a thunk if not equal
; fallthrough to GET_DESCRIPTOR if equal
GET_DESCRIPTOR:
; Just get the descriptor address into
; [RAMPZ:]Z, and the length into r16
; We know ALL descriptors are at the beginning of the bootloader, in the reset_vector space,
; and by inspection we can determine that they all share the same high byte of the address (0x7EXX)
ldi ZH, 0x7E ; Load ZH with the most significant 8 bits of the descriptors address (0x7E)
; High byte of wValue for GET_DESCRIPTOR transactions specifies Descriptor Type
; NOTE! We are skipping the comparison for 0x01 (Device Descriptor), since that can't really
; be excluded, we simply assume that's the default to save space here. See @SAVE_SPACE below.
cpi reg_wValueH, 0x02 ; Compare high byte of wValue with value 2;
breq send_config_descriptor ; If high byte of wValue is 0x02 (Configuration Descriptor), jump to handle that
cpi reg_wValueH, 0x21 ; Compare high byte of wValue with value 0x21;
breq send_hid_descriptor ; If high byte of wValue is 0x21 (HID Class HID Descriptor), jump to handle that
cpi reg_wValueH, 0x22 ; Compare high byte of wValue with value 0x22;
breq send_hid_report_descriptor ; If high byte of wValue is 0x22 (HID Class HID Report Descriptor), jump to handle that
; If needed, include other descriptors here
; @SAVE_SPACE: I was able to comment this out and things still work, but it's probably bad (saves 6 bytes)
; The following 2 lines are also dropped since we are skipping "rjmp UNHANDLED_SETUP_REQUEST" (osamuaoki)
; cpi reg_wValueH, 0x01 ; Compare high byte of wValue with value 1;
; breq send_device_descriptor ; If high byte of wValue is 0x01 (Device Descriptor), jump to handle that
; NOTE: Originally, only this rjmp was skipped and things were still working, that's what
; osamuaoki was able to use to optimize the check for (Device Descriptor), and simply fall through.
; rjmp UNHANDLED_SETUP_REQUEST ; If the requested descriptor is not supported jump to UNHANDLED_SETUP_REQUEST
send_device_descriptor:
; We only load the lower portion (lo8) of the address of the descriptor,
; the higher portion is common for all descriptors
ldi ZL, lo8(device_descriptor) ; Load ZL with the least significant 8 bits of device_descriptor
rjmp process_single_descriptor ; jump to process_single_descriptor
send_config_descriptor:
; We only load the lower portion (lo8) of the address of the descriptor,
; the higher portion is common for all descriptors
ldi ZL, lo8(config_descriptor) ; Load ZL with the least significant 8 bits of config_descriptor
ldi r16, 34 ; Load r16 with length of config_descriptor (34 bytes)
rjmp process_descriptor ; jump to process_descriptor
send_hid_report_descriptor:
; We only load the lower portion (lo8) of the address of the descriptor,
; the higher portion is common for all descriptors
ldi ZL, lo8(hid_report_descriptor); Load ZL with the least significant 8 bits of hid_report_descriptor
ldi r16, 21 ; Load r16 with length of hid_report_descriptor (21 bytes)
rjmp process_descriptor ; jump to process_descriptor
; If needed, include other descriptors here
send_hid_descriptor:
; We only load the lower portion (lo8) of the address of the descriptor,
; the higher portion is common for all descriptors
ldi ZL, lo8(hid_descriptor) ; Load ZL with the least significant 8 bits of hid_descriptor
process_single_descriptor:
lpm r16, Z ; Load r16 with the first byte of descriptor, which contains its length in bytes
process_descriptor:
; Acknowledge the SETUP packet
rcall clear_RXSTPI ; This function uses r17 to clear the RXSTPI bit in UEINTX
verifyMaxDescriptorLength:
cp reg_wLengthL, r16 ; Compare the value in r24 (wLengthL) against the value in r16 (length of descriptor to send)
brlo send_descriptor ; If the value in reg_wLengthL is smaller, use it to send the descriptor, jump to that tag
mov reg_wLengthL, r16 ; Otherwise, copy the value in r16 (which is the smaller of the two) to reg_wLengthL, and use that to send the descriptor
send_descriptor:
; Abort if RXSTPI is set
ldd r17, Y+oUEINTX ; Load r17 with the value in the USB Endpoint Interrupt Register (UEINTX);
sbrc r17, RXSTPI ; Skip the next instruction if the Received SETUP Interrupt Flag (RXSTPI) is cleared
reti ; Return if RXSTPI is set, we need to prioritize SETUP packets
; NOTE: R17 already has the most current value of UEINTX, no need to load it again
sbrs r17, RXOUTI ; Skip the next instruction if the Received OUT Data Interrupt Flag (RXOUTI) is set (there's an OUT packet from the host)