device.doc

Device driver structure

One:
        Device header

For each supported memory type:
        Disk I/O
        (Memory alloc)
        (Query free)
        Disk I/O memory class structure

For each unit:
        Unit structure and configuration
        Used memory structures

If not appended:
        Device driver function pointers
        Device driver functions




Sample device source:

                org     0
; The following is to be considered as both a device driver header and
; as a starting point for the configuration table. This driver will be
; identified by its segment address and this structure must be at offset
; 0.

                ; Device driver header
drhdr_next      dd      -1              ; Pointer to next device (now last)
drhdr_attr      dw      DR_ATTRIBUTES
drhdr_strategy  dw      offset strategy ; Offset to strategy function
drhdr_commands  dw      offset commands ; Offset to commands function
drhdr_units     db      1               ; Number of units

; The rest has four functions to be considered
;  1) usable as device driver name if this driver is changed
;     into character device on init.
;  2) usable as a label to be returned in media check call
;  3) identifies this device driver as SRDISK driver by always having
;     the letters SRD at offset dr_ID
;  4) identifies the memory used by the 4 char string at offset dr_memory

dr_volume       label byte
dr_ID           db 'SRD'                ; SRDISK signature (3 char)
dr_memory       db MEMSTR               ; Memory type identifier (4 char)
dr_version      db SRD_VERSION          ; Device driver version (4 char)
                db 0                    ; null to end volume label
dr_v_format     db V_FORMAT             ; Configuration format version
dr_conf         dw offset conf          ; Pointer to 1st unit configuration