read.z80

;; Read sequential records from a file.
;;
;; Given a filename open it, and read 256 records to it - testing that the contents
;; match what we expect.
;;
;;  A record of 0x00
;;  A record of 0x01
;; ..
;;  A record of 0xFF
;;
;;

FCB1:                EQU 0x5C
DMA:                 EQU 0x80
DMA_LEN:             EQU 128
BDOS_ENTRY_POINT:    EQU 5
BDOS_OUTPUT_STRING:  EQU 9
BDOS_READ_FILE:      EQU 20
BDOS_OPEN_FILE:      EQU 15
BDOS_CLOSE_FILE:     EQU 16

; Simple macro to push all (important) registers.
;
MACRO PUSH_ALL
        push af
        push bc
        push de
        push hl
      ENDM


;
; Simple macro to pop all (important) registers.
;
MACRO POP_ALL
        pop hl
        pop de
        pop bc
        pop af
      ENDM
; }}


       ORG 0x0100

       ;; The FCB will be populated with the pattern/first argument,
       ;; if the first character of that region is a space-character
       ;; then we've got nothing to search for.
       ld a, (FCB1 + 1)
       cp 0x20             ; 0x20 = 32 == SPACE
       jp nz, got_argument ; Not a space, so we can proceed

        ;;
        ;; No argument, so show the error and exit
        ;;
        ld de, usage_message
        ld c,  BDOS_OUTPUT_STRING
        call   BDOS_ENTRY_POINT

exit_fn:
        LD      C,0x00
        CALL    BDOS_ENTRY_POINT


got_argument:
        ;; Open the file
        LD DE, FCB1
        LD C, BDOS_OPEN_FILE
        CALL BDOS_ENTRY_POINT

        ;; Did that succeed?
        cp 00
        jr z, open_ok

        LD DE, OPEN_FAILED
        ld c,  BDOS_OUTPUT_STRING
        call   BDOS_ENTRY_POINT
        jr exit_fn

open_ok:
        ;; Right here we loop from 0x00 - 0xFF starting at 0x00
        ld a, 0x00
read_record:
        PUSH AF
             ; read a record
             LD C, BDOS_READ_FILE
             LD DE, FCB1
             CALL BDOS_ENTRY_POINT

        POP AF

        ; Does this record contain the current record number?
        LD HL, DMA
        LD b,(HL)
        CP B
        JR NZ, RECORD_FAILED

        INC A
        cp 0
        jr nz, read_record

        ;; Close the file
        LD DE,FCB1
        LD C, BDOS_CLOSE_FILE
        CALL BDOS_ENTRY_POINT

        ;; Exit
        jr exit_fn

RECORD_FAILED:
        push af
        ld de, FAILURE
        ld c,  BDOS_OUTPUT_STRING
        call   BDOS_ENTRY_POINT

        pop af
        call show_a_register

           ld c, 0x02
           ld e, 0x0a
           call 0x0005
           ld c, 0x02
           ld e, 0x0d
           call 0x0005

        ; now dump the memory
        ld b, 128
        ld hl, DMA
show_mem:
        push bc
        ld a,(hl)
           call show_a_register
           ld c, 0x02
           ld e, " "
           call 0x0005
        pop bc
        djnz show_mem
        jr exit_fn


DispHL:
        ld      c,-10
        call    Num1
        ld      c,-1
Num1:   ld      a,'0'-1
Num2:   inc     a
        add     hl,bc
        jr      c,Num2
        sbc     hl,bc
        PUSH_ALL
        ld e, a
        ld c, 0x02
        call 0x0005
        POP_ALL
        ret

show_a_register:
        ld h,0
        ld l,a
        call DispHL
        ret

usage_message:
        db "Usage: READ FILENAME.EXT"
        ;; note fall-through here :)
newline:
        db 0xa, 0xd, "$"
FAILURE:
        db "Unexpected value reading file at record $"

OPEN_FAILED:
        db "opening the file failed.", 0x0a, 0x0d, "$"

RECORD:
        DB 0x00
END