From 172ce143498cd810816e12d19f835ecf2d309ec5 Mon Sep 17 00:00:00 2001
From: Greg King <gregdk@users.sf.net>
Date: Sun, 25 Aug 2013 00:31:36 -0400
Subject: [PATCH] Made an exec() program-chaining function for the Commodore
 libraries.

---
 libsrc/cbm/exec.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 libsrc/cbm/exec.c

diff --git a/libsrc/cbm/exec.c b/libsrc/cbm/exec.c
new file mode 100644
index 000000000..302115c17
--- /dev/null
+++ b/libsrc/cbm/exec.c
@@ -0,0 +1,99 @@
+/*
+** Program-chaining function for Commodore platforms.
+**
+** 2013-08-24, Greg King
+**
+** This function exploits the program-chaining feature in CBM BASIC's ROM.
+** It puts the desired program's name and unit number into a LOAD statement.
+** Then, it points BASIC to that statement, so that the ROM will run that
+** statement after this program quits.  The ROM will load the next program,
+** and execute it.
+*/
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <device.h>
+#if   defined(__CBM610__)
+#  include <cbm610.h>
+#elif defined(__CBM510__)
+#  include <cbm510.h>
+#endif
+
+
+#pragma data-name(push, "LOWCODE")
+static struct line {
+    const char end_of_line;
+    const struct line *const next;
+    const unsigned line_num;
+    const char load_token, quotes[2], add_token, quote;
+    char name[21];
+    const char comma;
+    char unit[3];
+} basic = {
+    '\0', &basic + 1,           /* high byte must be non-zero */
+    0, 0x93,
+
+    /* This string operation copies the name to high BASIC RAM.
+    ** So, it won't be overwritten when the next program is loaded.
+    */
+    "\"\"", 0xaa, '\"',
+    "\"                    ",   /* format: "123:1234567890123456\"" */
+    ',', "01"
+};
+#pragma data-name(pop)
+
+/* These values are platform-specific. */
+extern const struct line *txtptr;
+#pragma zpsym("txtptr")
+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;
+
+    /* Exclude devices that can't load files. */
+    dv = getcurrentdevice ();
+    if (dv < 8 && dv != 1 || dv > 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;
+    }
+    close (fd);
+
+    do {
+        if ((basic.name[n] = progname[n]) == '\0') {
+            break;
+        }
+    } while (++n < 20);         /* truncate long names */
+    basic.name[n] = '\"';
+
+    /* Build the next program's argument list. */
+    basbuf[0] = 0x8f;           /* REM token */
+    basbuf[1] = '\0';
+    if (cmdline != NULL) {
+        strncat (basbuf, cmdline, (size_t)basbuf_len - 2);
+    }
+
+#if defined(__CBM510__) || defined(__CBM610__)
+    pokewsys ((unsigned)&txtptr, (unsigned)&basic);
+#else
+    txtptr = &basic;
+#endif
+
+    /* (The return code, in ST, will be destroyed by LOAD.
+    ** So, don't bother to set it here.)
+    */
+    exit (__AX__);
+}
-- 
2.39.2