From 5263696a44cc4f2c23e53dd68af0c66efd1fd896 Mon Sep 17 00:00:00 2001
From: Ian C <ianc@noddybox.co.uk>
Date: Thu, 11 Apr 2024 18:22:46 +0100
Subject: Added Vic-20 PRG output.  Not sure BASIC stub is needed so checkin
 prior to removal.

---
 src/example/Makefile  |  5 ++++-
 src/example/vic20.asm | 24 +++++++++++++++++++++++
 src/prgout.c          | 54 +++++++++++++++++++++++++++++++++++++++++++++------
 3 files changed, 76 insertions(+), 7 deletions(-)
 create mode 100644 src/example/vic20.asm

diff --git a/src/example/Makefile b/src/example/Makefile
index 700e9e5..629314a 100644
--- a/src/example/Makefile
+++ b/src/example/Makefile
@@ -21,7 +21,7 @@
 #
 
 ALL	= spectrum.tap t64.t64 zx81.p gb.gb vcs.bin snes.sfc nes.nes cpc.cdt \
-	  prg.prg hex.hex
+	  prg.prg hex.hex vic20.prg
 CASM	= ../casm
 
 all: $(ALL) $(CASM)
@@ -61,6 +61,9 @@ prg.prg: prg.asm $(CASM)
 hex.hex: emucpm.z80 $(CASM)
 	$(CASM) emucpm.z80
 
+vic20.prg: vic20.asm $(CASM)
+	$(CASM) vic20.asm
+
 clean:
 	rm -f $(ALL)
 
diff --git a/src/example/vic20.asm b/src/example/vic20.asm
new file mode 100644
index 0000000..8bb222d
--- /dev/null
+++ b/src/example/vic20.asm
@@ -0,0 +1,24 @@
+	; Simple example C64 code
+	;
+
+	cpu 6502
+
+	option	codepage,cbm
+
+	option	output-file,vic20.prg
+	option	output-format,prg
+	option	prg-start,start
+        option  prg-system,vic20
+
+	org $1100
+
+main:
+	lda	#0
+	clc
+loop:
+	sta	36879
+	adc	#1
+	jmp	loop
+
+start:
+	jmp	main
diff --git a/src/prgout.c b/src/prgout.c
index d752c08..da14cae 100644
--- a/src/prgout.c
+++ b/src/prgout.c
@@ -39,23 +39,42 @@
 */
 enum option_t
 {
-    OPT_START_ADDR
+    OPT_START_ADDR,
+    OPT_SYSTEM_TYPE
 };
 
 static const ValueTable option_set[]=
 {
     {"prg-start", OPT_START_ADDR},
+    {"prg-system", OPT_SYSTEM_TYPE},
+    {NULL}
+};
+
+typedef enum
+{
+    SYS_C64,
+    SYS_VIC20,
+    SYS_VIC20_8K
+} system_t;
+
+static ValueTable system_table[]=
+{
+    {"c64",     SYS_C64},
+    {"vic20",   SYS_VIC20},
+    {"vic20+8k",SYS_VIC20_8K},
     {NULL}
 };
 
 typedef struct
 {
     int		start_addr;
+    system_t    system;
 } Options;
 
 static Options options =
 {
-    -1
+    -1,
+    SYS_C64
 };
 
 
@@ -110,6 +129,7 @@ const ValueTable *PRGOutputOptions(void)
 CommandStatus PRGOutputSetOption(int opt, int argc, char *argv[],
                                  int quoted[], char *err, size_t errsize)
 {
+    const ValueTable *val;
     CommandStatus stat = CMD_OK;
 
     CMD_ARGC_CHECK(1);
@@ -120,6 +140,11 @@ CommandStatus PRGOutputSetOption(int opt, int argc, char *argv[],
             CMD_EXPR(argv[0], options.start_addr);
             break;
 
+        case OPT_SYSTEM_TYPE:
+            CMD_TABLE(argv[0], system_table, val);
+            options.system = val->value;
+            break;
+
         default:
             break;
     }
@@ -140,7 +165,8 @@ int PRGOutput(const char *filename, const char *filename_bank,
         Byte *mem;
         int min, max, len;
         char sys[16];
-        int addr = 0x803;
+        int addr;
+        int start_addr;
         int next;
 
         if (count == 1)
@@ -159,13 +185,29 @@ int PRGOutput(const char *filename, const char *filename_bank,
             return FALSE;
         }
 
+        switch(options.system)
+        {
+            case SYS_C64:
+                addr = 0x803;
+                start_addr = 0x801;
+                break;
+            case SYS_VIC20:
+                addr = 0x1003;
+                start_addr = 0x1001;
+                break;
+            case SYS_VIC20_8K:
+                addr = 0x1203;
+                start_addr = 0x1201;
+                break;
+        }
+
         mem = bank[f]->memory;
         min = bank[f]->min_address_used;
         max = bank[f]->max_address_used;
 
         /* We're going to prepend some BASIC
         */
-        if (min < 0x810)
+        if (min < (addr + 0x10))
         {
             snprintf(error, error_size, "Bank starts below a safe "
                                         "area to add BASIC loader");
@@ -191,9 +233,9 @@ int PRGOutput(const char *filename, const char *filename_bank,
 
         addr = PokeW(mem, addr, 0x00);
 
-        PokeW(mem, 0x801, next);
+        PokeW(mem, start_addr, next);
 
-        min = 0x801;        /* Start of BASIC */
+        min = start_addr;        /* Start of BASIC */
 
         len = max - min + 1;
 
-- 
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