zasm: change ioRewind to ioSeek

Will need it soon.

apps/zasm/io.asm

@@ -22,8 +22,7 @@ ioPutC:
 	ld	ix, (IO_OUT_PUTC)
 	jp	(ix)
 
-ioRewind:
-	ld	hl, 0
+ioSeek:
 	ld	ix, (IO_IN_SEEK)
 	jp	(ix)
 

apps/zasm/main.asm

@@ -75,7 +75,8 @@ zasmMain:
 	call	zasmParseFile
 	ret	nz
 	; Second pass
-	call	ioRewind
+	ld	hl, 0
+	call	ioSeek
 	xor	a
 	ld	(ZASM_FIRST_PASS), a
 	call	zasmParseFile

tools/emul/zasm.c

@@ -27,7 +27,7 @@
 // in sync with zasm_glue.asm
 #define USER_CODE 0x4800
 #define STDIO_PORT 0x00
-#define STDIN_REWIND 0x01
+#define STDIN_SEEK 0x01
 
 // Other consts
 #define STDIN_BUFSIZE 0x8000
@@ -41,6 +41,7 @@ static uint8_t mem[0x10000];
 static uint8_t inpt[STDIN_BUFSIZE];
 static int inpt_size;
 static int inpt_ptr;
+static uint8_t received_first_seek_byte = 0;
 
 static uint8_t io_read(int unused, uint16_t addr)
 {
@@ -65,8 +66,14 @@ static void io_write(int unused, uint16_t addr, uint8_t val)
 #ifndef MEMDUMP
         putchar(val);
 #endif
-    } else if (addr == STDIN_REWIND) {
-        inpt_ptr = 0;
+    } else if (addr == STDIN_SEEK) {
+        if (received_first_seek_byte) {
+            inpt_ptr |= val;
+            received_first_seek_byte = 0;
+        } else {
+            inpt_ptr = (val << 8) & 0xff00;
+            received_first_seek_byte = 1;
+        }
     } else {
         fprintf(stderr, "Out of bounds I/O write: %d / %d\n", addr, val);
     }

tools/emul/zasm_glue.asm

@@ -2,7 +2,7 @@
 .equ RAMSTART		0x4000
 .equ USER_CODE		0x4800
 .equ STDIO_PORT		0x00
-.equ STDIN_REWIND	0x01
+.equ STDIN_SEEK		0x01
 
 jr	init	; 2 bytes
 ; *** JUMP TABLE ***
@@ -43,7 +43,12 @@ emulPutC:
 	ret
 
 emulSeek:
-	out	(STDIN_REWIND), a
+	; the STDIN_SEEK port works by poking it twice. First poke is for high
+	; byte, second poke is for low one.
+	ld	a, h
+	out	(STDIN_SEEK), a
+	ld	a, l
+	out	(STDIN_SEEK), a
 	ret
 
 #include "core.asm"