Initial support for a PET target (#109)

* Initial support for a PET target

* Created user-definable symbol for RAM size to add support for 8k and 16k PETs

* Added variables to the commodore linker file to be defined in the concrete targets specifying the start and end of the free zero page

* Pushed zero page flag in clang.cfg down from commodore into concrete targets as all targets no longer share the same amount of free zero page

* Added mention of PET support to README

README.md

@@ -11,6 +11,7 @@ The LLVM-MOS compiler toolchain and platform libraries.
   - 8-KiB or 16-KiB standard cartridge
 - Commander X16
 - Commodore 64
+- Commodore PET
 - MEGA65
 - NES
   - NES-NROM
@@ -119,6 +120,7 @@ executables and libraries for that target.
 | Atari 8-bit Standard cartridge | `mos-atari8-stdcart`  |
 | Commander X16                  | `mos-cx16-clang`      |
 | Commodore 64                   | `mos-c64-clang`       | 
+| Commodore PET                  | `mos-pet-clang`       |
 | MEGA65                         | `mos-mega65-clang`    |
 | NES-CNROM                      | `mos-nes-cnrom-clang` |
 | NES-MMC1                       | `mos-nes-mmc1-clang`  |

mos-platform/CMakeLists.txt

@@ -60,3 +60,4 @@ add_subdirectory(nes-mmc1)
 add_subdirectory(nes-mmc3)
 add_subdirectory(osi-c1p)
 add_subdirectory(dodo)
+add_subdirectory(pet)

mos-platform/c64/clang.cfg

@@ -1 +1,2 @@
+-mlto-zp=110
 -D__C64__

mos-platform/c64/link.ld

@@ -5,6 +5,9 @@
  * Produces a PRG file with a SYS command to start the program.
  */
 
+__basic_zp_start = 0x0002;
+__basic_zp_end = 0x0090;
+
 MEMORY {
     ram (rw) : ORIGIN = 0x0801, LENGTH = 0xC7FF
 }

mos-platform/commodore/clang.cfg

@@ -1,2 +1 @@
--mlto-zp=110
 -D__CBM__

mos-platform/commodore/commodore.ld

@@ -6,11 +6,11 @@
  */
 
 /* Provide imaginary (zero page) registers in the BASIC area. */
-__rc0 = 0x0002;
+__rc0 = __basic_zp_start;
 INCLUDE imag-regs.ld
-ASSERT(__rc31 == 0x0021, "Inconsistent zero page map.")
+ASSERT(__rc31 == (__rc0 + 0x1F), "Inconsistent zero page map.")
 
-MEMORY { zp : ORIGIN = __rc31 + 1, LENGTH = 0x90 - (__rc31 + 1) }
+MEMORY { zp : ORIGIN = __rc31 + 1, LENGTH = __basic_zp_end - (__rc31 + 1) }
 
 INPUT(basic-header.o)
 

mos-platform/cx16/clang.cfg

@@ -1,2 +1,3 @@
+-mlto-zp=110
 -D__CX16__
 -mcpu=mos65c02

mos-platform/cx16/link.ld

@@ -5,6 +5,9 @@
  * Produces a PRG file with a SYS command to start the program.
  */
 
+__basic_zp_start = 0x0002;
+__basic_zp_end = 0x0090;
+
 MEMORY {
     ram (rw) : ORIGIN = 0x0801, LENGTH = 0x96ff
 }

mos-platform/mega65/clang.cfg

@@ -1,2 +1,3 @@
+-mlto-zp=110
 -D__MEGA65__
 -mcpu=mos65ce02

mos-platform/mega65/link.ld

@@ -3,6 +3,9 @@
  * Produces a PRG file with a SYS command to start the program.
  */
 
+__basic_zp_start = 0x0002;
+__basic_zp_end = 0x0090;
+
 MEMORY {
     /*
      * Allocate in $2001 - $7fff (bank 0)

mos-platform/pet/CMakeLists.txt

@@ -0,0 +1,12 @@
+platform(pet COMPLETE HOSTED PARENT commodore)
+
+if(NOT CMAKE_CROSSCOMPILING)
+  return()
+endif()
+
+install(FILES link.ld TYPE LIB)
+
+add_platform_object_file(pet-basic-header basic-header.o basic-header.S)
+
+add_platform_library(pet-c kernal.S)
+target_include_directories(pet-c BEFORE PUBLIC .)

mos-platform/pet/basic-header.S

@@ -0,0 +1,13 @@
+; PET BASIC header that jumps to _start                            
+
+.section .basic_header,"aR",@progbits
+        .short next_line        ; address of next BASIC line                                 
+        .short 7773             ; line number: l33t for LLVM, a hint that this program was   
+                                                ; compiled with LLVM                         
+        .byte 0x9e                      ; SYS keyword BASIC token                            
+        .mos_addr_asciz _start, 4       ; the location of the _start symbol, in 4 decimal    
+                                                ; ASCII digits                               
+next_line:
+        .short 0                        ; end of basic program                               
+
+

mos-platform/pet/clang.cfg

@@ -0,0 +1,2 @@
+-mlto-zp=107
+-D__PET__

mos-platform/pet/kernal.S

@@ -0,0 +1,32 @@
+; Copyright 2022 LLVM-MOS Project                                                                        
+; Licensed under the Apache License, Version 2.0 with LLVM Exceptions,                                   
+; See https://github.com/llvm-mos/llvm-mos-sdk/blob/main/LICENSE for license                             
+; information.                                                                                           
+
+; Originally from cc65. Modified from original version.                                                  
+
+;                                                                                                        
+; Ullrich von Bassewitz, 19.11.2002                                                                      
+;                                                                                                        
+; PET Kernal functions                                                                                   
+;                                                                                                        
+
+#define __PET__ 1
+#include <cbm_kernal.inc>
+
+.macro weakdef name:req
+  .weak \name
+  __\name = \name
+  .global __\name
+.endm
+
+weakdef CLRCH
+weakdef BASIN
+weakdef CHRIN
+weakdef STOP
+weakdef GETIN
+weakdef CLALL
+weakdef UDTIM
+weakdef CHROUT
+weakdef BSOUT
+weakdef CHRIN

mos-platform/pet/link.ld

@@ -0,0 +1,28 @@
+/* Commodore PET PRG file linker script.                                                                 
+ *                                                                                                       
+ * Produces a PRG file with a SYS command to start the program.                                          
+ */
+
+PROVIDE(__ram_size = 32);
+ASSERT(__ram_size <= 32,
+       "RAM size must be <= 32 (8x96 and SuperPETs are not supported by this target)")
+ASSERT(__ram_size >= 8,
+       "RAM size must be at least 8")
+
+__basic_zp_start = 0x0002;
+__basic_zp_end = 0x008D;
+
+MEMORY {
+    ram (rw) : ORIGIN = 0x0401, LENGTH = (__ram_size * 1024) - 0x0401
+}
+
+INCLUDE commodore.ld
+
+/* Grow stack downwards from end of RAM */
+__stack = (__ram_size * 1024) - 1;
+
+OUTPUT_FORMAT {
+    /* Tells the PET LOAD command where to place the file's contents. */
+    SHORT(0x0401)
+    TRIM(ram)
+}