/*
** Program-chaining function for Commodore platforms.
**
-** 2013-09-04, Greg King
+** 2015-09-27, Greg King
**
** This function exploits the program-chaining feature in CBM BASIC's ROM.
**
/* The struct below is a line of BASIC code. It sits in the LOWCODE segment
** to make sure that it won't be hidden by a ROM when BASIC is re-enabled.
** The line is:
-** 0 LOAD""+"" ,01
+** 0 CLR:LOAD""+"" ,01
** After this function has written into the line, it might look like this:
-** 0 LOAD""+"program name" ,08
+** 0 CLR:LOAD""+"program name" ,08
**
** When BASIC's LOAD command asks the Kernal to load a file, it gives the
** Kernal a pointer to a file-name string. CC65's CBM programs use that
** pointer to give a copy of the program's name to main()'s argv[0] parameter.
-** But, when BASIC uses a string literal that's in a program, it points
+** But, when BASIC uses a string literal that is in a program, it points
** directly to that literal -- in the models that don't use banked RAM
** (Pet/CBM, VIC-20, and 64). The literal is overwritten by the next program
-** that's loaded. So, argv[0] would point to machine code. String operations
+** that is loaded. So, argv[0] would point to machine code. String operations
** create a new result string -- even when that operation changes nothing. The
** result is put in the string space at the top of BASIC's memory. So, the ""+
** in this BASIC line guarantees that argv[0] will get a name from a safe place.
*/
#pragma data-name(push, "LOWCODE")
static struct line {
- const char end_of_line;
- const struct line *const next;
+ const char end_of_line; /* fake previous line */
+ const struct line* const next;
const unsigned line_num;
- const char load_token, quotes[2], add_token, quote;
+ const char CLR_token, colon, LOAD_token, quotes[2], add_token, quote;
char name[21];
const char comma;
char unit[3];
} basic = {
- '\0', &basic + 1, /* high byte of link must be non-zero */
- 0, 0x93, "\"\"", 0xaa, '\"',
- "\" ", /* format: "123:1234567890123456\"" */
+ '\0', &basic + 1, /* high byte of link must be non-zero */
+ 0, 0x9C, ':', 0x93, "\"\"", 0xAA, '\"',
+ "\" ", /* format: "123:1234567890123456\"" */
',', "01"
};
#pragma data-name(pop)
/* These values are platform-specific. */
-extern const struct line *txtptr;
+extern const void* vartab; /* points to BASIC program variables */
+#pragma zpsym("vartab")
+extern const void* memsize; /* points to top of BASIC RAM */
+#pragma zpsym("memsize")
+extern const struct line* txtptr; /* points to BASIC code */
#pragma zpsym("txtptr")
-extern char basbuf[]; /* BASIC's input buffer */
+extern char basbuf[]; /* BASIC's input buffer */
extern void basbuf_len[];
#pragma zpsym("basbuf_len")
int __fastcall__ exec (const char* progname, const char* cmdline)
{
static int fd;
- static unsigned char dv, n = 0;
+ static unsigned char dv, n;
/* Exclude devices that can't load files. */
+ /* (Use hand optimization, to make smaller code.) */
dv = getcurrentdevice ();
- if (dv < 8 && dv != 1 || dv > 30) {
+ if (dv < 8 && __AX__ != 1 || __AX__ > 30) {
return _mappederrno (9); /* illegal device number */
}
utoa (dv, basic.unit, 10);
- /* Don't try to run a program that can't be found. */
- fd = open (progname, O_RDONLY);
- if (fd < 0) {
- return fd;
+ /* Tape files can be openned only once; skip this test for the Datasette. */
+ if (dv != 1) {
+ /* Don't try to run a program that can't be found. */
+ fd = open (progname, O_RDONLY);
+ if (fd < 0) {
+ return -1;
+ }
+ close (fd);
}
- close (fd);
+ n = 0;
do {
if ((basic.name[n] = progname[n]) == '\0') {
break;
}
- } while (++n < 20); /* truncate long names */
+ } while (++n < 20); /* truncate long names */
basic.name[n] = '\"';
+/* This next part isn't needed by machines that put
+** BASIC source and variables in different RAM banks.
+*/
+#if !defined(__CBM510__) && !defined(__CBM610__) && !defined(__C128__)
+ /* cc65 program loads might extend beyond the end of the RAM that is allowed
+ ** for BASIC. Then, the LOAD statement would complain that it is "out of
+ ** memory". Some pointers that say where to put BASIC program variables
+ ** must be changed, so that we do not get that error. One pointer is
+ ** changed here; a BASIC CLR statement changes the others.
+ */
+ vartab = (char*)memsize - 256;
+#endif
+
/* Build the next program's argument list. */
- basbuf[0] = 0x8f; /* REM token */
+ basbuf[0] = 0x8F; /* REM token */
basbuf[1] = '\0';
if (cmdline != NULL) {
strncat (basbuf, cmdline, (size_t)basbuf_len - 2);
}
+ /* Tell the ROM where to find that BASIC program. */
#if defined(__CBM510__) || defined(__CBM610__)
pokewsys ((unsigned)&txtptr, (unsigned)&basic);
#else
txtptr = &basic;
#endif
- /* (The return code, in ST, will be destroyed by LOAD.
+ /* (The return code, in ST [status], will be destroyed by LOAD.
** So, don't bother to set it here.)
*/
exit (__AX__);
projects / cc65 / commitdiff