zasm: allow .org to be specified from command line

Also important for upcoming mega commit...

apps/zasm/README.md

@@ -3,6 +3,21 @@
 This is probably the most critical part of the Collapse OS project because it
 ensures its self-reproduction.
 
+## Invocation
+
+`zasm` is invoked with 2 mandatory arguments and an optional one. The mandatory
+arguments are input blockdev id and output blockdev id. For example, `zasm 0 1`
+reads source code from blockdev 0, assembles it and spit the result in blockdev
+1.
+
+Input blockdev needs to be seek-able, output blockdev doesn't need to (zasm
+writes in one pass, sequentially.
+
+The 3rd argument, optional, is the initial `.org` value. It's the high byte of
+the value. For example, `zasm 0 1 4f` assembles source in blockdev 0 as if it
+started with the line `.org 0x4f00`. This also means that the initial value of
+the `@` symbol is `0x4f00`.
+
 ## Running on a "modern" machine
 
 To be able to develop zasm efficiently, [libz80][libz80] is used to run zasm

apps/zasm/main.asm

@@ -8,14 +8,17 @@
 ; whether we're in "local pass", that is, in local label scanning mode. During
 ; this special pass, ZASM_FIRST_PASS will also be set so that the rest of the
 ; code behaves as is we were in the first pass.
-.equ	ZASM_LOCAL_PASS		ZASM_FIRST_PASS+1
+.equ	ZASM_LOCAL_PASS		@+1
 ; What IO_PC was when we started our context
-.equ	ZASM_CTX_PC		ZASM_LOCAL_PASS+1
+.equ	ZASM_CTX_PC		@+1
 ; current ".org" offset, that is, what we must offset all our label by.
-.equ	ZASM_ORG		ZASM_CTX_PC+2
-.equ	ZASM_RAMEND		ZASM_ORG+2
+.equ	ZASM_ORG		@+2
+.equ	ZASM_RAMEND		@+2
 
 ; Takes 2 byte arguments, blkdev in and blkdev out, expressed as IDs.
+; Can optionally take a 3rd argument which is the high byte of the initial
+; .org. For example, passing 0x42 to this 3rd arg is the equivalent of beginning
+; the unit with ".org 0x4200".
 ; Read file through blkdev in and outputs its upcodes through blkdev out.
 ; HL is set to the last lineno to be read.
 ; Sets Z on success, unset on error. On error, A contains an error code (ERR_*)
@@ -23,7 +26,7 @@ zasmMain:
 	; Parse args. HL points to string already
 	; We don't allocate memory just to hold this. Because this happens
 	; before initialization, we don't really care where those args are
-	; parsed.
+	; parsed. That's why we borrow zasm's RAMSTART for a little while.
 	ld	de, .argspecs
 	ld	ix, ZASM_RAMSTART
 	call	parseArgs
@@ -44,11 +47,18 @@ zasmMain:
 	ld	de, IO_OUT_BLK
 	call	blkSel
 
-	; Init modules
+	; Init .org
+	; This is the 3rd argument, optional, will be zero if not given.
+	; Save in "@" too
+	ld	a, (ZASM_RAMSTART+2)
+	ld	(ZASM_ORG+1), a		; high byte of .org
+	ld	(DIREC_LASTVAL+1), a
 	xor	a
+	ld	(ZASM_ORG), a		; low byte zero in all cases
+	ld	(DIREC_LASTVAL), a
+
+	; And then the rest.
 	ld	(ZASM_LOCAL_PASS), a
-	ld	(ZASM_ORG), a
-	ld	(ZASM_ORG+1), a
 	call	ioInit
 	call	symInit
 
@@ -73,7 +83,7 @@ zasmMain:
 	jp	ioLineNo		; --> HL, --> DE, returns
 
 .argspecs:
-	.db	0b001, 0b001, 0
+	.db	0b001, 0b001, 0b101
 .sFirstPass:
 	.db	"First pass", 0
 .sSecondPass:

tools/emul/zasm/glue.asm

@@ -56,13 +56,20 @@ init:
 	ld	de, BLOCKDEV_SEL
 	call	blkSel
 	call	fsOn
+	; There's a special understanding between zasm.c and this unit: The
+	; addresses 0xff00 and 0xff01 contain the two ascii chars to send to
+	; zasm as the 3rd argument.
+	ld	a, (0xff00)
+	ld	(.zasmArgs+4), a
+	ld	a, (0xff01)
+	ld	(.zasmArgs+5), a
 	ld	hl, .zasmArgs
 	call	USER_CODE
 	; signal the emulator we're done
 	halt
 
 .zasmArgs:
-	.db	"0 1", 0
+	.db	"0 1 XX", 0
 
 ; *** I/O ***
 emulGetB:

tools/emul/zasm/zasm.c

@@ -1,5 +1,6 @@
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 #include "../libz80/z80.h"
 #include "kernel-bin.h"
 #include "zasm-bin.h"
@@ -8,8 +9,11 @@
  * in another specified blkdev. In our emulator layer, we use stdin and stdout
  * as those specified blkdevs.
  *
- * This executable takes one argument: the path to a .cfs file to use for
- * includes.
+ * This executable takes two arguments. Both are optional, but you need to
+ * specify the first one if you want to get to the second one.
+ * The first one is the value to send to z80-zasm's 3rd argument (the initial
+ * .org). Defaults to '00'.
+ * The second one is the path to a .cfs file to use for includes.
  *
  * Because the input blkdev needs support for Seek, we buffer it in the emulator
  * layer.
@@ -155,7 +159,7 @@ static void mem_write(int unused, uint16_t addr, uint8_t val)
 
 int main(int argc, char *argv[])
 {
-    if (argc > 2) {
+    if (argc > 3) {
         fprintf(stderr, "Too many args\n");
         return 1;
     }
@@ -166,9 +170,19 @@ int main(int argc, char *argv[])
     for (int i=0; i<sizeof(USERSPACE); i++) {
         mem[i+USER_CODE] = USERSPACE[i];
     }
+    char *init_org = "00";
+    if (argc >= 2) {
+        init_org = argv[1];
+        if (strlen(init_org) != 2) {
+            fprintf(stderr, "Initial org must be a two-character hex string");
+        }
+    }
+    // glue.asm knows that it needs to fetch these arguments at this address.
+    mem[0xff00] = init_org[0];
+    mem[0xff01] = init_org[1];
     fsdev_size = 0;
-    if (argc == 2) {
-        FILE *fp = fopen(argv[1], "r");
+    if (argc == 3) {
+        FILE *fp = fopen(argv[2], "r");
         if (fp == NULL) {
             fprintf(stderr, "Can't open file %s\n", argv[1]);
             return 1;

tools/zasm.sh

@@ -1,9 +1,30 @@
 #!/usr/bin/env bash
 
+# Calls tools/emul/zasm/zasm in a convenient manner by wrapping specified
+# paths to include in a single CFS file and then pass that file to zasm.
+# Additionally, it takes a "-o" argument to set the initial ".org" of the
+# binary. For example, "zasm.sh -o 4f < foo.asm" assembles foo.asm as if it
+# started with the line ".org 0x4f00".
+
 # readlink -f doesn't work with macOS's implementation
 # so, if we can't get readlink -f to work, try python with a realpath implementation
 ABS_PATH=$(readlink -f "$0" || python -c "import os; print(os.path.realpath('$0'))")
 
+usage() { echo "Usage: $0 [-o <hexorg>] <paths-to-include>..." 1>&2; exit 1; }
+
+org='00'
+while getopts ":o:" opt; do
+    case "${opt}" in
+        o)
+            org=${OPTARG}
+            ;;
+        *)
+            usage
+            ;;
+    esac
+done
+shift $((OPTIND-1))
+
 # wrapper around ./emul/zasm/zasm that prepares includes CFS prior to call
 DIR=$(dirname "${ABS_PATH}")
 ZASMBIN="${DIR}/emul/zasm/zasm"
@@ -16,7 +37,7 @@ for p in "$@"; do
     "${CFSPACK}" "${p}" "*.bin" >> "${INCCFS}"    
 done
 
-"${ZASMBIN}" "${INCCFS}"
+"${ZASMBIN}" "${org}" "${INCCFS}"
 RES=$?
 rm "${INCCFS}"
 exit $RES