zasm: add .out directive

apps/zasm/README.md

@@ -127,6 +127,13 @@ allowed. An included file cannot have an `#inc` directive.
           explicitly with `.fill`, if needed. Often used to assemble binaries
           designed to run at offsets other than zero (userland).
 
+**.out**: Outputs the value of the expression supplied as an argument to
+          `ZASM_DEBUG_PORT`. The value is always interpreted as a word, so
+          there's always two `out` instruction executed per directive. High byte
+          is sent before low byte. Useful or debugging, quickly figuring our
+          RAM constants, etc. The value is only outputted during the second
+          pass.
+
 **#inc**: Takes a string literal as an argument. Open the file name specified
           in the argument in the currently active filesystem, parse that file
           and output its binary content as is the code has been in the includer

apps/zasm/const.asm

@@ -19,3 +19,6 @@
 
 ; Out of memory
 .equ	ERR_OOM			0x07
+
+; *** Other ***
+.equ	ZASM_DEBUG_PORT		42

apps/zasm/directive.asm

@@ -5,7 +5,8 @@
 .equ	D_EQU	0x02
 .equ	D_ORG	0x03
 .equ	D_FIL	0x04
-.equ	D_INC	0x05
+.equ	D_OUT	0x05
+.equ	D_INC	0x06
 .equ	D_BAD	0xff
 
 ; *** Variables ***
@@ -20,6 +21,7 @@ directiveNames:
 	.db	".EQU"
 	.db	".ORG"
 	.db	".FIL"
+	.db	".OUT"
 	.db	"#inc"
 
 ; This is a list of handlers corresponding to indexes in directiveNames
@@ -29,6 +31,7 @@ directiveHandlers:
 	.dw	handleEQU
 	.dw	handleORG
 	.dw	handleFIL
+	.dw	handleOUT
 	.dw	handleINC
 
 handleDB:
@@ -187,6 +190,33 @@ handleFIL:
 	call	unsetZ
 	ret
 
+handleOUT:
+	push	hl
+	; Read our expression
+	call	readWord
+	jr	nz, .badfmt
+	call	zasmIsFirstPass		; No .out during first pass
+	jr	z, .end
+	ld	hl, scratchpad
+	call	parseExpr
+	jr	nz, .badarg
+	push	ix \ pop hl
+	ld	a, h
+	out	(ZASM_DEBUG_PORT), a
+	ld	a, l
+	out	(ZASM_DEBUG_PORT), a
+	jr	.end
+.badfmt:
+	ld	a, ERR_BAD_FMT
+	jr	.error
+.badarg:
+	ld	a, ERR_BAD_ARG
+.error:
+	call	unsetZ
+.end:
+	pop	hl
+	ret
+
 handleINC:
 	call	readWord
 	jr	nz, .badfmt