written code for reading file from SD card, not tested yet

src/dos_m65/dev_sdcard/fs_hvsr_read_file.s

@@ -49,12 +49,90 @@ fs_hvsr_read_file_open:
 
 	; Found the file - load it
 
-	; XXX provide implementation
+	jsr fs_hvsr_direntmem_restore     ; restore $1000 memory content
 
+	lda #$18                          ; dos_openfile
+	sta HTRAP00
+	+nop
 
+	; XXX check error code
 
-	jmp dos_EXIT_CLC
+	; XXX check for errors
 
+	; Read the first 512-byte chunk
+
+	lda #$03                 ; mode: read file
+	sta SD_MODE
+
+	jsr fs_hvsr_read_file
+	jmp dos_EXIT
+
+fs_hvsr_read_file:
+
+	; Read chunk of data to SD card buffer
+
+	lda #$1A                          ; dos_readfile
+	sta HTRAP00
+	+nop
+
+	; XXX check error code
+
+	; Store number of bytes read
+
+	stx SD_ACPTR_LEN+0
+	sty SD_ACPTR_LEN+1
+
+	; Check if any data was read
+
+	lda SD_ACPTR_LEN+0
+	ora SD_ACPTR_LEN+0
+	bne @copy
+
+	lda #$20                          ; dos_closefile
+	sta HTRAP00
+	+nop
+
+	lda #$00
+	sec
+	rts
+
+@copy:
+
+	; Set pointer to new data
+
+	lda #<SD_FILEBUF
+	sta SD_ACPTR_PTR+0
+	lda #>SD_FILEBUF
+	sta SD_ACPTR_PTR+1
+
+	; Copy data to SD_FILEBUF
+
+	lda #%10000000                    ; select SD card buffer
+	tsb SD_BUFCTL
+
+	lda #$02
+	sta DMA_ADDRBANK                  ; $D702
+	lda #$00
+	sta DMA_ADDRMB                    ; $D704
+
+	lda #>(@dmalist-$4000)
+	sta DMA_ADDRMSB                   ; $D701
+	lda #<(@dmalist-$4000)
+	sta DMA_ETRIG                     ; $D705
+
+	clc
+	rts
+
+@dmalist:
+
+	!byte $0A                         ; use F018A list format (it is shorter by 1 byte)
+	!byte $80, $FF                    ; src. address is $FFxxxxx
+	!byte $81, $00                    ; dst. address is $00xxxxx
+	!byte $00                         ; end of options
+	!byte $00                         ; operation: COPY
+	!word $0200                       ; data size if 512 bytes
+	!byte $00, $6E, $0D               ; src. addr is $xxD6E00
+	!byte <SD_FILEBUF, >SD_FILEBUF - $80, $01 ; dst. addr is $xx1xxxx (internal buffer)
 
 fs_hvsr_file_not_found: