Build drive selection logic for FCBs

boot/kernel.asm

@@ -3,6 +3,7 @@
 
 %include	"inc/bpb.asm"
 %include	"inc/mbr.asm"
+%include	"inc/fcb.asm"
 
 		; kernel stack size in words
 %define		stacksize 512
@@ -22,18 +23,30 @@ print_banner:	mov si, banner
 		cmp al, 0x0D
 		jnz .loop
 
+		cmp dl, 0x80
+		jc .k
+		sub dl, (0x80-2)
+.k:		mov [defdrv], dl
+
 		call dskrst
 
-		mov dl, 0
-		call dsksel
+		mov bx, testfcb
+		call fcbfst
 
 hlt:		hlt
 		jmp hlt
 
+%include	"kernel/fcb.asm"
+%include        "kernel/drive.asm"
+
+section .data
+
 %defstr VERSIONSTR VERSION
 banner:		db "RDOS ", VERSIONSTR, 0x0A, 0x0D
 
-%include        "kernel/drive.asm"
+testfcb:	db 0
+		db "HELLO   ", "COM"
+		times 30 db 0
 
 section .bss
 

inc/fcb.asm

@@ -0,0 +1,10 @@
+struc fcb
+.drive		resb 1
+.filename	resb 8
+.type		resb 3
+.fn2		resb 8
+.tp2		resb 3
+.dirpos		resw 1
+.cluster	resw 1
+.recordnum	resb 1
+endstruc

kernel/drive.asm

@@ -1,6 +1,6 @@
 section .bss
 
-		; drive selected for I/O
+		; drive actually selected for I/O
 dsknum:		resb 1
 		; current sector number
 dskseek:	resd 1

kernel/fcb.asm

@@ -1,8 +1,23 @@
-; in FCB required
-; word	offset in rootdir
-;	used for search
-; word	current cluster
-; byte	record num in cluster
+section .bss
+
+		; default drive if field in FCB = 0
+defdrv:		resb 1
+
+section .text
+		; Functions here generally expect the FCB to be at ES:BX
+
+		; Helper function: read the drive number from FCB,
+		; apply default if necessary,
+		; and make it current I/O drive
+setdrv:		mov dl, [es:bx+fcb.drive] ; A=1
+		test dl, dl
+		jnz .nofix
+		mov dl, [defdrv] ; A=0
+		inc dl
+		mov [es:bx+fcb.drive], dl ; A=1
+		; now set as current i/o drive
+.nofix:		dec dl ; A=0 for dsksel
+		jmp dsksel
 
 		; FCB open
 fcbopn:		; call fcbfst
@@ -16,12 +31,10 @@ fcbcls:		; flush disk buffer
 		ret
 
 		; FCB find first
-fcbfst:		; init search state in FCB
-		; jmp to fcbnxt
-		ret
-
+fcbfst:		mov word [es:bx+fcb.dirpos], 0
 		; FCB find next
-fcbnxt:		; load rootdir sector from state
+fcbnxt:		call setdrv
+		; load rootdir sector from state
 		; search until next match
 		; next sec & loop if mismatch
 		; err exit if no further matches
@@ -31,6 +44,7 @@ fcbnxt:		; load rootdir sector from state
 fcbdel:		; call fcbfst
 		; get search state, load root dir from there
 		; mark file as deleted
+		; mark buffer dirty
 		ret
 
 		; FCB read