bac80.c: use 0xFE38 = 65080 = ERRCODE as a junk byte

ERRCODE will immediately be reset to -1 on END anyway, so it is a
perfectly safe place to dump an unwanted value.

1 files changed, 11 insertions, 8 deletions

diff --git a/bac80.c b/bac80.c
index 5327dbd..160e5e5 100644
--- a/bac80.c
+++ b/bac80.c
@@ -132,24 +132,28 @@ static uint8_t run_prefix[] = {
 #define RUN_CALL_OFFSET 15
 
 /*
- * This is the BASIC statement 1 POKE xxxx%,CALL(yyyy%)
- * followed by an end of program marker (1 byte) and a scratch byte.
+ * This is the BASIC statement 1 POKE 65080%,CALL(yyyy%)
+ * followed by an end of program marker (1 byte).  65080% is
+ * the location of ERRCODE, which will be reset to -1 when
+ * END is executed anyway, which will happen immediately.
  *
  * This includes the BASIC statement encapsulation, since this is
  * part of the payload.
  */
 static uint8_t restart_prefix[] = {
-    0x11, 0x01, 0x00, 0x86, 0x81, 0xc7,
-    0xff, 0xff,			/* Point to scratch byte */
+    0x10, 0x01, 0x00, 0x86, 0x81, 0xc7,
+    0x38, 0xfe,			/* Point to scratch byte */
     0xba, 0x2c, 0xc7,
     0, 0,			/* CALL address goes here */
     0xce, 0x3a, 0xba, 0x0d,
-    0x01,			/* End of BASIC program */
-    0x00			/* Scratch byte */
+    0x01			/* End of BASIC program */
 };
-#define RESTART_REL1_OFFSET 6
 #define RESTART_CALL_OFFSET 11
 
+/*
+ * STOP statement, used as end-of-data marker.  Technically,
+ * any BASIC statement of 3 bytes or less would work here.
+ */
 static const uint8_t stop_stmt[] = {
     0x86, 0x89			/* BASIC bytecode for STOP */
 };
@@ -182,7 +186,6 @@ int writebac80(FILE * out, const uint8_t * data, int len, int origin,
             /* Application, add a restart prefix to payload */
             pfxlen = sizeof restart_prefix;
             set16(restart_prefix + RESTART_CALL_OFFSET, entrypoint);
-	    push_reloc(RESTART_REL1_OFFSET - pfxlen);
             push_reloc(RESTART_CALL_OFFSET - pfxlen);
         }
         loader[bac80r_SYM_DELTA] = pfxlen;