From a260d0a806467866ed94a39ec75ab67de6fb0305 Mon Sep 17 00:00:00 2001
From: Karol Stasiak <karol.m.stasiak@gmail.com>
Date: Fri, 12 Nov 2021 02:45:53 +0100
Subject: [PATCH] CBM BASIC loader should use the actual address of main (fixes
 #111)

---
 docs/api/commodore-programming-guide.md |  5 ++++
 docs/lang/preprocessor.md               |  2 ++
 include/cbm/basic_loader.mfk            | 31 +++++++++++++++++++++++++
 include/loader_0401.mfk                 | 20 +---------------
 include/loader_0801.mfk                 | 20 +---------------
 include/loader_0801_16bit.mfk           |  3 ++-
 include/loader_1001.mfk                 | 20 +---------------
 include/loader_1201.mfk                 | 20 +---------------
 include/loader_1c01.mfk                 | 20 +---------------
 9 files changed, 45 insertions(+), 96 deletions(-)
 create mode 100644 include/cbm/basic_loader.mfk

diff --git a/docs/api/commodore-programming-guide.md b/docs/api/commodore-programming-guide.md
index e597c08c..3aee9a49 100644
--- a/docs/api/commodore-programming-guide.md
+++ b/docs/api/commodore-programming-guide.md
@@ -2,6 +2,11 @@
 
 ### A note about Commodore 64
 
+#### Unusual main function location
+
+If you're creating a prg file and your `main` function may be located at address $2710 hex (10000 decimal) or higher,
+you might need to define the `DISPLACED_MAIN=1` preprocessor feature. 
+
 #### Multifile programs
 
 A multifile program is a program stored on a disk that consists of the main program file that is executed first
diff --git a/docs/lang/preprocessor.md b/docs/lang/preprocessor.md
index c1d29948..482588bf 100644
--- a/docs/lang/preprocessor.md
+++ b/docs/lang/preprocessor.md
@@ -103,6 +103,8 @@ Some libraries may require that some of these be defined.
 
 * `KEYBOARD` – 1 if the target has a keyboard, 0 otherwise
 
+* `DISPLACED_MAIN` – set this to 1 if the `main` function is in a very unusual location for the target
+
 * `USE_MOUSE_MBM` –  set this to 1 if you want to enable middle button support for the mouse. 
 
 * `JOYSTICKS` – the maximum number of joysticks using standard hardware configurations, may be 0
diff --git a/include/cbm/basic_loader.mfk b/include/cbm/basic_loader.mfk
new file mode 100644
index 00000000..80ad12a1
--- /dev/null
+++ b/include/cbm/basic_loader.mfk
@@ -0,0 +1,31 @@
+#template $ADDR$
+
+#if not(CBM)
+#warn cbm/basic_loader module should be only used on Commodore targets
+#endif
+
+const array _basic_loader @ $ADDR$ = [
+#if DISPLACED_MAIN
+    @word_le [
+        $ADDR$ + 0xB
+    ],
+#else
+    @word_le [
+        $ADDR$ + if(main.addr >= 10000, 1/0, 0xA) // use -D DISPLACED_MAIN=1 if you get an error here
+    ],
+#endif
+    10,
+    0,
+    $9e,
+#if DISPLACED_MAIN
+    $30 + (main.addr/10000)%%10,
+#endif
+    $30 + (main.addr/1000)%%10,
+    $30 + (main.addr/100)%%10,
+    $30 + (main.addr/10)%%10,
+    $30 + (main.addr/1)%%10,
+    0,
+    0,
+    0
+    ]
+
diff --git a/include/loader_0401.mfk b/include/loader_0401.mfk
index 40f4a6b2..b95b0f1a 100644
--- a/include/loader_0401.mfk
+++ b/include/loader_0401.mfk
@@ -1,19 +1 @@
-#if not(CBM)
-#warn loader_0401 module should be only used on Commodore targets
-#endif
-
-const array _basic_loader @$401 = [
-    $0b,
-    4,
-    10,
-    0,
-    $9e,
-    $31,
-    $30,
-    $33,
-    $37,
-    0,
-    0,
-    0
-    ]
-
+import cbm/basic_loader<$401>
diff --git a/include/loader_0801.mfk b/include/loader_0801.mfk
index 82ddd414..eac63fed 100644
--- a/include/loader_0801.mfk
+++ b/include/loader_0801.mfk
@@ -1,19 +1 @@
-#if not(CBM)
-#warn loader_0801 module should be only used on Commodore targets
-#endif
-
-const array _basic_loader @$801 = [
-    $0b,
-    $08,
-    10,
-    0,
-    $9e,
-    $32,
-    $30,
-    $36,
-    $31,
-    0,
-    0,
-    0
-    ]
-
+import cbm/basic_loader<$801>
diff --git a/include/loader_0801_16bit.mfk b/include/loader_0801_16bit.mfk
index 3ea6df22..d531c7b0 100644
--- a/include/loader_0801_16bit.mfk
+++ b/include/loader_0801_16bit.mfk
@@ -22,4 +22,5 @@ asm void __init_16bit() @$80D {
     clc
     xce
     sep #$30
-}
\ No newline at end of file
+    jmp main
+}
diff --git a/include/loader_1001.mfk b/include/loader_1001.mfk
index e15ed4fc..74b003c3 100644
--- a/include/loader_1001.mfk
+++ b/include/loader_1001.mfk
@@ -1,19 +1 @@
-#if not(CBM)
-#warn loader_1001 module should be only used on Commodore targets
-#endif
-
-const array _basic_loader @$1001 = [
-    $0b,
-    $10,
-    10,
-    0,
-    $9e,
-    $34,
-    $31,
-    $30,
-    $39,
-    0,
-    0,
-    0
-    ]
-
+import cbm/basic_loader<$1001>
diff --git a/include/loader_1201.mfk b/include/loader_1201.mfk
index ae668bff..7cf1083e 100644
--- a/include/loader_1201.mfk
+++ b/include/loader_1201.mfk
@@ -1,19 +1 @@
-#if not(CBM)
-#warn loader_1201 module should be only used on Commodore targets
-#endif
-
-const array _basic_loader @$1201 = [
-    $0b,
-    $12,
-    10,
-    0,
-    $9e,
-    $34,
-    $36,
-    $32,
-    $31,
-    0,
-    0,
-    0
-    ]
-
+import cbm/basic_loader<$1201>
diff --git a/include/loader_1c01.mfk b/include/loader_1c01.mfk
index 7f6c9c77..fa01b773 100644
--- a/include/loader_1c01.mfk
+++ b/include/loader_1c01.mfk
@@ -1,19 +1 @@
-#if not(CBM)
-#warn loader_1c01 module should be only used on Commodore targets
-#endif
-
-const array _basic_loader @$1C01 = [
-    $0b,
-    $1C,
-    10,
-    0,
-    $9e,
-    $37,
-    $31,
-    $38,
-    $31,
-    0,
-    0,
-    0
-    ]
-
+import cbm/basic_loader<$1c01>