shell: implement seek and peek

This introduces `core.asm` which includes routines used by other parts.

parts/core.asm

@@ -0,0 +1,193 @@
+; core
+;
+; Routines used by pretty much all parts. You will want to include it first
+; in your glue file.
+
+; *** CONSTS ***
+ASCII_CR	.equ	0x0d
+ASCII_LF	.equ	0x0a
+
+; *** CODE ***
+
+; add the value of A into DE
+addDE:
+	add	a, e
+	jr	nc, .end	; no carry? skip inc
+	inc	d
+.end:
+	ld	e, a
+	ret
+
+; Format the lower nibble of A into a hex char and stores the result in A.
+fmtHex:
+	and	a, 0xf
+	cp	10
+	jr	nc, .alpha	; if >= 10, we have alpha
+	add	a, '0'
+	ret
+.alpha:
+	add	a, 'A'-10
+	ret
+
+; Formats value in A into a string hex pair. Stores it in the memory location
+; that HL points to. Does *not* add a null char at the end.
+fmtHexPair:
+	push	af
+
+	; let's start with the rightmost char
+	inc	hl
+	call	fmtHex
+	ld	(hl), a
+
+	; and now with the leftmost
+	dec	hl
+	pop	af
+	push	af
+	and	a, 0xf0
+	rra \ rra \ rra \ rra
+	call	fmtHex
+	ld	(hl), a
+
+	pop	af
+	ret
+
+; jump to the location pointed to by HL. This allows us to call HL instead of
+; just jumping it.
+jumpHL:
+	jp	hl
+	ret
+
+; Parse the hex char at A and extract it's 0-15 numerical value. Put the result
+; in A.
+;
+; On success, the carry flag is reset. On error, it is set.
+parseHex:
+	; First, let's see if we have an easy 0-9 case
+	cp	'0'
+	jr	c, .error	; if < '0', we have a problem
+	cp	'9'+1
+	jr	nc, .alpha	; if >= '9'+1, we might have alpha
+	; We are in the 0-9 range
+	sub	a, '0'		; C is clear
+	ret
+
+.alpha:
+	call	upcase
+	cp	'A'
+	jr	c, .error	; if < 'A', we have a problem
+	cp	'F'+1
+	jr	nc, .error	; if >= 'F', we have a problem
+	; We have alpha.
+	sub	a, 'A'-10	; C is clear
+	ret
+
+.error:
+	scf
+	ret
+
+; Parses 2 characters of the string pointed to by HL and returns the numerical
+; value in A. If the second character is a "special" character (<0x21) we don't
+; error out: the result will be the one from the first char only.
+;
+; On success, the carry flag is reset. On error, it is set.
+parseHexPair:
+	push	bc
+	push	hl
+
+	ld	a, (hl)
+	call	parseHex
+	jr	c, .end		; error? goto end, keeping the C flag on
+	rla \ rla \ rla \ rla	; let's push this in MSB
+	ld	b, a
+	inc	hl
+	ld	a, (hl)
+	;cp	0x21
+	;jr	c, .single	; special char? single digit
+	call	parseHex
+	jr	c, .end		; error?
+	or	b		; join left-shifted + new. we're done!
+	; C flag was set on parseHex and is necessarily clear at this point
+	jr	.end
+
+.single:
+	; If we have a single digit, our result is already stored in B, but
+	; we have to right-shift it back.
+	ld	a, b
+	and	a, 0xf0
+	rra \ rra \ rra \ rra
+
+.end:
+	pop	hl
+	pop	bc
+	ret
+
+; print null-terminated string pointed to by HL
+printstr:
+	push	af
+	push	hl
+
+.loop:
+	ld	a, (hl)		; load character to send
+	or	a		; is it zero?
+	jr	z, .end		; if yes, we're finished
+	call	aciaPutC
+	inc	hl
+	jr	.loop
+
+.end:
+	pop	hl
+	pop	af
+	ret
+
+; print A characters from string that HL points to
+printnstr:
+	push	bc
+	push	hl
+
+	ld	b, a
+.loop:
+	ld	a, (hl)		; load character to send
+	call	aciaPutC
+	inc	hl
+	djnz	.loop
+
+.end:
+	pop	hl
+	pop	bc
+	ret
+
+; Compares strings pointed to by HL and DE up to A count of characters. If
+; equal, Z is set. If not equal, Z is reset.
+strncmp:
+	push	bc
+	push	hl
+	push	de
+
+	ld	b, a
+.loop:
+	ld	a, (de)
+	cp	(hl)
+	jr	nz, .end	; not equal? break early
+	inc	hl
+	inc	de
+	djnz	.loop
+
+.end:
+	pop	de
+	pop	hl
+	pop	bc
+	; Because we don't call anything else than CP that modify the Z flag,
+	; our Z value will be that of the last cp (reset if we broke the loop
+	; early, set otherwise)
+	ret
+
+; Transforms the character in A, if it's in the a-z range, into its upcase
+; version.
+upcase:
+	cp	'a'
+	ret	c	; A < 'a'. nothing to do
+	cp	'z'+1
+	ret	nc	; A >= 'z'+1. nothing to do
+	; 'a' - 'A' == 0x20
+	sub	0x20
+	ret

parts/shell.asm

@@ -13,8 +13,6 @@
 ; See constants below for error codes.
 
 ; *** CONSTS ***
-CR	.equ	0x0d
-LF	.equ	0x0a
 
 ; number of entries in shellCmdTbl
 SHELL_CMD_COUNT	.equ	2
@@ -25,8 +23,19 @@ SHELL_ERR_UNKNOWN_CMD	.equ	0x01
 ; Arguments for the command weren't properly formatted
 SHELL_ERR_BAD_ARGS	.equ	0x02
 
+; *** VARIABLES ***
+; Memory address that the shell is currently "pointing at" for peek and deek
+; operations. Set with seek.
+SHELL_MEM_PTR	.equ	SHELL_RAMSTART
+; Used to store formatted hex values just before printing it.
+SHELL_HEX_FMT	.equ	SHELL_MEM_PTR+2
+SHELL_RAMEND	.equ	SHELL_HEX_FMT+2
+
 ; *** CODE ***
 shellInit:
+	xor	a
+	ld	(SHELL_MEM_PTR), a
+
 	; print prompt
 	ld	hl, .prompt
 	call	printstr
@@ -40,32 +49,14 @@ shellLoop:
 	call	chkbuf
 	jr	shellLoop
 
-; print null-terminated string pointed to by HL
-printstr:
-	push	af
-	push	hl
-
-.loop:
-	ld	a, (hl)		; load character to send
-	or	a		; is it zero?
-	jr	z, .end		; if yes, we're finished
-	call	aciaPutC
-	inc	hl
-	jr	.loop
-
-.end:
-	pop	hl
-	pop	af
-	ret
 
 printcrlf:
-	ld	a, CR
+	ld	a, ASCII_CR
 	call	aciaPutC
-	ld	a, LF
+	ld	a, ASCII_LF
 	call	aciaPutC
 	ret
 
-
 ; check if the input buffer is full or ends in CR or LF. If it does, prints it
 ; back and empty it.
 chkbuf:
@@ -81,9 +72,9 @@ chkbuf:
 	ld	a, (hl)		; now, that's our char we have in A
 	inc	hl		; put HL back where it was
 
-	cp	CR
+	cp	ASCII_CR
 	jr	z, .do		; char is CR? do!
-	cp	LF
+	cp	ASCII_LF
 	jr	z, .do		; char is LF? do!
 
 	; nothing matched? don't do anything
@@ -101,51 +92,12 @@ chkbuf:
 	call	shellParse
 	ret
 
-; Compares strings pointed to by HL and DE up to A count of characters. If
-; equal, Z is set. If not equal, Z is reset.
-strncmp:
-	push	bc
-	push	hl
-	push	de
-
-	ld	b, a
-.loop:
-	ld	a, (de)
-	cp	(hl)
-	jr	nz, .end	; not equal? break early
-	inc	hl
-	inc	de
-	djnz	.loop
-
-.end:
-	pop	de
-	pop	hl
-	pop	bc
-	; Because we don't call anything else than CP that modify the Z flag,
-	; our Z value will be that of the last cp (reset if we broke the loop
-	; early, set otherwise)
-	ret
-
-; add the value of A into DE
-addDE:
-	add	a, e
-	jr	nc, .end	; no carry? skip inc
-	inc	d
-.end:
-	ld	e, a
-	ret
-
-; jump to the location pointed to by HL. This allows us to call HL instead of
-; just jumping it.
-jumpHL:
-	jp	hl
-	ret
-
 ; Parse command (null terminated) at HL and calls it
 shellParse:
 	push	af
 	push	bc
 	push	de
+	push	hl
 
 	ld	de, shellCmdTbl
 	ld	a, SHELL_CMD_COUNT
@@ -165,19 +117,34 @@ shellParse:
 	jr	.end
 
 .found:
+	; all right, we're almost ready to call the cmd. Let's just have DE
+	; point to the cmd jump line.
 	ld	a, 4
 	call	addDE
-	ex	hl, de
+	; Now, let's swap HL and DE because, welll because that's how we're set.
+	ex	hl, de	; HL = jump line, DE = cmd str pointer
+
+	; Before we call our command, we want to set up the pointer to the arg
+	; list. Normally, it's DE+5 (DE+4 is the space) unless DE+4 is null,
+	; which means no arg.
+	ld	a, 4
+	call	addDE
+	ld	a, (DE)
+	cp	0
+	jr	z, .noarg	; char is null? we have no arg
+	inc	de
+.noarg:
+	; DE points to args, HL points to jump line. Ready to roll!
 	call	jumpHL
-	ex	hl, de
 
 .end:
+	pop	hl
 	pop	de
 	pop	bc
 	pop	af
 	ret
 
-; Print the error code set in A (doesn't work for codes > 9 yet...)
+; Print the error code set in A (in hex)
 shellPrintErr:
 	push	af
 	push	hl
@@ -185,9 +152,10 @@ shellPrintErr:
 	ld	hl, .str
 	call	printstr
 
-	; ascii for '0' is 0x30
-	add	a, 0x30
-	call	aciaPutC
+	ld	hl, SHELL_HEX_FMT
+	call	fmtHexPair
+	ld	a, 2
+	call	printnstr
 	call	printcrlf
 
 	pop	hl
@@ -198,19 +166,66 @@ shellPrintErr:
 	.db	"ERR ", 0
 
 ; *** COMMANDS ***
+; When these commands are called, DE points to the first character of the
+; command args.
+
+; Set memory pointer to the specified address.
+; Example: seek 01fe
+
 shellSeek:
-	ld	hl, .str
-	call	printstr
+	push	de
+	push	hl
+
+	ex	de, hl
+	call	parseHexPair
+	jr	c, .error
+	ld	(SHELL_MEM_PTR), a
+	inc	hl
+	inc	hl
+	call	parseHexPair
+	jr	c, .error
+	ld	(SHELL_MEM_PTR+1), a
+	jr	.success
+
+.error:
+	ld	a, SHELL_ERR_BAD_ARGS
+	call	shellPrintErr
+	jr	.end
+
+.success:
+	ld	a, (SHELL_MEM_PTR)
+	ld	hl, SHELL_HEX_FMT
+	call	fmtHexPair
+	ld	a, 2
+	call	printnstr
+	ld	a, (SHELL_MEM_PTR+1)
+	call	fmtHexPair
+	ld	a, 2
+	call	printnstr
+	call	printcrlf
+
+.end:
+	pop	hl
+	pop	de
 	ret
-.str:
-	.db	"seek called", CR, LF, 0
 
+
+; peek byte where memory pointer points to aby display its value
 shellPeek:
-	ld	hl, .str
-	call	printstr
+	push	af
+	push	hl
+
+	ld	hl, (SHELL_MEM_PTR)
+	ld	a, (hl)
+	ld	hl, SHELL_HEX_FMT
+	call	fmtHexPair
+	ld	a, 2
+	call	printnstr
+	call	printcrlf
+
+	pop	hl
+	pop	af
 	ret
-.str:
-	.db	"peek called", CR, LF, 0
 
 ; Format: 4 bytes name followed by 2 bytes jump. fill names with zeroes
 shellCmdTbl:

recipes/rc2014.md

@@ -47,7 +47,7 @@ This is what your glue code would look like:
 	jr	init
 
 .fill	0x38-$
-	jr	aciaInt
+	jp	aciaInt
 
 init:
 	di
@@ -63,8 +63,10 @@ init:
 	ei
 	call	shellLoop
 
+#include "core.asm"
 ACIA_RAMSTART	.equ	RAMSTART
 #include "acia.asm"
+SHELL_RAMSTART	.equ	ACIA_RAMEND
 #include "shell.asm"
 ```
 
@@ -83,11 +85,9 @@ We set interrupt mode to 1 because that's what `acia.asm` is written around.
 Then, we init ACIA, shell, enable interrupt and give control of the main loop
 to `shell.asm`.
 
-What comes below is actual code include from the acia and shell modules. As you
-can see, we need to tell each module where to put their variables. `shell.asm`
-doesn't have variables, but if it did, we would have a `SHELL_RAMSTART .equ
-ACIA_RAMEND` just below the `acia.asm` include. `ACIA_RAMEND` is defined in
-`acia.asm`.
+What comes below is actual code include from parts we want to include in our
+OS. As you can see, we need to tell each module where to put their variables.
+See `parts/README.md` for details.
 
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