From 9f8538b5dcf44976052b7a7a5d3f0dc8f33048cb Mon Sep 17 00:00:00 2001
From: kris <kris.kennaway@gmail.com>
Date: Fri, 12 May 2017 00:23:08 +0100
Subject: [PATCH] Initial skeleton of an Apple II simulator to be used for
 tracing boot1 execution.  This traps writes to text page 1 and reads/writes
 to high memory (>$C000).

This is already sufficient to trace the execution of one of the simple
boot1 images that clears the text page (manually) and writes 'THIS DISK
HAS NO DOS TO BOOT'
---
 sim_apple2.py | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 sim_apple2.py

diff --git a/sim_apple2.py b/sim_apple2.py
new file mode 100644
index 0000000..378db71
--- /dev/null
+++ b/sim_apple2.py
@@ -0,0 +1,55 @@
+"""Partial simulation of Apple II"""
+
+from py65.devices import mpu65c02
+from py65 import memory
+
+class AppleII(object):
+    def __init__(self):
+        # TODO: should trap by default
+        self.memory = memory.ObservableMemory()
+        self.cpu = mpu65c02.MPU(memory=self.memory)
+
+        # Set up interceptors for accessing various interesting parts of the memory map
+
+        # Text page 1
+        self.memory.subscribe_to_write(xrange(0x400, 0x7ff), self.TextPageWriteInterceptor)
+
+        self.memory.subscribe_to_write(xrange(0xc000, 0xffff), self.TraceWriteInterceptor)
+        self.memory.subscribe_to_read(xrange(0xc000, 0xffff), self.TraceReadInterceptor)
+
+    # TODO: convert addresses to screen coordinates
+    def TextPageWriteInterceptor(self, address, value):
+        print 'Wrote "%s" to text page address $%04X' % (chr(value & 0x7f), address)
+
+    def TraceWriteInterceptor(self, address, value):
+        print 'Wrote "%s" to address $%04X' % (chr(value), address)
+
+    def TraceReadInterceptor(self, address):
+        print 'Read from address $%04X' % address
+
+    def Run(self, pc):
+        self.cpu.pc = pc
+        while True:
+            self.cpu.step(trace=False)
+            if self.cpu.pc == pc:
+                break
+            pc = self.cpu.pc
+
+
+def main():
+
+    boot1 = [
+        0x01, 0x8d, 0xe8, 0xc0, 0x8d, 0x51, 0xc0, 0x8d, 0x54, 0xc0, 0xa0, 0x00, 0xa9, 0xa0, 0x99, 0x00,
+        0x04, 0x99, 0x00, 0x05, 0x99, 0x00, 0x06, 0x99, 0x00, 0x07, 0xc8, 0xd0, 0xf1, 0xa9, 0x08, 0x85,
+        0x01, 0xa9, 0x33, 0x85, 0x00, 0xb1, 0x00, 0xf0, 0x08, 0x09, 0x80, 0x99, 0xaf, 0x05, 0xc8, 0xd0,
+        0xec, 0xf0, 0xfe, 0x54, 0x48, 0x49, 0x53, 0x20, 0x44, 0x49, 0x53, 0x4b, 0x20, 0x48, 0x41, 0x53,
+        0x20, 0x4e, 0x4f, 0x20, 0x42, 0x4f, 0x4f, 0x54, 0x20, 0x43, 0x4f, 0x44, 0x45, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    ]
+
+    apple2 = AppleII()
+    apple2.memory[0x800:0x800+len(boot1)] = boot1
+    apple2.Run(0x801)
+
+if __name__ == '__main__':
+    main()
\ No newline at end of file