some work towards PRG file loading via CBDOS

src/dos_m65/dev_sdcard/fs_hvsr_read_file.s

@@ -0,0 +1,72 @@
+
+;
+; Hypervisor virtual filesystem - opening the file
+;
+
+
+fs_hvsr_read_file_open:
+
+	; Open the directory
+
+	lda #$12                          ; dos_opendir
+	sta HTRAP00
+	+nop
+
+	; XXX handle read errors
+
+	sta SD_DESC                       ; store directory descriptor  XXX invent better name
+
+	; Reset status to OK
+
+	lda #$00
+	sta PAR_TRACK
+	sta PAR_SECTOR
+	jsr util_status_SD
+
+	; XXX deduplicate part above with opening directory
+
+	; Read dirent structures into $1000, find the first matching file
+	; Starting at $1000 VIC sees chargen, so this should be a safe place
+
+	jsr fs_hvsr_direntmem_prepare
+
+@lp_find:
+
+	jsr fs_hvsr_util_nextdirentry      ; fetch the next file name
+	+bcs fs_hvsr_file_not_found
+
+	; Only accept files of type 'PRG'
+
+	lda PAR_FTYPE
+	and #%10111111 
+	cmp #$02
+	bne @lp_find
+
+	; Check if file name matches the filter
+
+	jsr util_dir_filter
+	bne @lp_find                       ; if does not match, try the next entry
+
+	; Found the file - load it
+
+	; XXX provide implementation
+
+
+
+	clc
+	rts
+
+fs_hvsr_file_not_found:
+
+	jsr fs_hvsr_direntmem_restore     ; restore $1000 memory content
+
+    ldx SD_DESC
+	lda #$16                          ; dos_closedir
+	sta HTRAP00
+	+nop
+
+	lda #39                           ; file not found error
+	jsr util_status_SD
+
+	sec
+	rts