basic: add bsel, bseek, getb, putb commands

apps/basic/README.md

@@ -165,6 +165,31 @@ Then, there's the *special stuff*. This is the list of things you can query for:
 As explained in "glueing" section abolve, this folder contains optional modules.
 Here's the documentation for them.
 
+### blk
+
+Block devices commands. Block devices are configured during kernel
+initialization and are referred to by numbers.
+
+**bsel**: Select the active block device. The active block device is the target
+of all commands below. You select it by specifying its number. For example,
+`bsel 0` selects the first configured device. `bsel 1` selects the second.
+
+A freshly selected blkdev begins with its "pointer" at 0.
+
+**seek**: Moves the blkdev "pointer" to the specified offset. The first
+argument is the offset's least significant half (blkdev supports 32-bit
+addressing). Is is interpreted as an unsigned integer.
+
+The second argument is optional and is the most significant half of the address.
+It defaults to 0.
+
+**getb**: Read a byte in active blkdev at current pointer, then advance the
+pointer by one. Read byte goes in `A`.
+
+**putb**: Writes a byte in active blkdev at current pointer, then advance the
+pointer by one. The value of the byte is determined by the expression supplied
+as an argument. Example: `putb 42`.
+
 ### fs
 
 `fs.asm` provides those commands:

apps/basic/blk.asm

@@ -0,0 +1,47 @@
+basBSEL:
+	call	rdExpr
+	ret	nz
+	push	ix \ pop hl
+	call	blkSelPtr
+	ld	a, l
+	jp	blkSel
+
+basBSEEK:
+	call	rdExpr
+	ret	nz
+	push	ix	; --> lvl 1
+	call	rdExpr
+	push	ix \ pop de
+	pop	hl	; <-- lvl 1
+	jr	z, .skip
+	; DE not supplied, set to zero
+	ld	de, 0
+.skip:
+	xor	a	; absolute mode
+	call	blkSeek
+	cp	a	; ensure Z
+	ret
+
+basGETB:
+	call	blkGetB
+	ret	nz
+	ld	(VAR_TBL), a
+	ret
+
+basPUTB:
+	call	rdExpr
+	ret	nz
+	push	ix \ pop hl
+	ld	a, l
+	jp	blkPutB
+
+basBLKCmds:
+	.dw	basBSEL
+	.db	"bsel", 0, 0
+	.dw	basBSEEK
+	.db	"bseek", 0
+	.dw	basGETB
+	.db	"getb", 0, 0
+	.dw	basPUTB
+	.db	"putb", 0, 0
+	.db	0xff, 0xff, 0xff	; end of table

tools/emul/bshell/glue.asm

@@ -86,6 +86,7 @@
 .inc "basic/buf.asm"
 .equ	BFS_RAMSTART	BUF_RAMEND
 .inc "basic/fs.asm"
+.inc "basic/blk.asm"
 .equ	BAS_RAMSTART	BFS_RAMEND
 .inc "basic/main.asm"
 
@@ -105,6 +106,9 @@ init:
 
 basFindCmdExtra:
 	ld	hl, basFSCmds
+	call	basFindCmd
+	ret	z
+	ld	hl, basBLKCmds
 	jp	basFindCmd
 
 emulGetC: