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39 lines
2.3 KiB
Org Mode
39 lines
2.3 KiB
Org Mode
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* 2013-02 - Building a 6502 emulator
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1. Download the latest copy of Klaus Dormann's amazing 6502 functional tests.
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- Easy-to-look-at (old) version: https://github.com/redline6561/cl-6502/blob/master/tests/6502_functional_test.a65
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- Announcement and discussion on 6502.org: http://forum.6502.org/viewtopic.php?f=2&t=2241
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- Source: http://2m5.de/6502_Emu/index.htm
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2. Figure out how to compile them using as65
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- Download: http://www.kingswood-consulting.co.uk/assemblers/
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- If you're on Mac OS, running Ubuntu in a VirtualBox with a shared folder might be the easiest way.
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3. Create a skeleton CPU, memory interface, etc. and write a loop that loads and interprets instructions.
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- No need to implement any instructions yet: just make it fail on unknown instructions.
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- Also, make it exit if it gets stuck on the same instruction, since that's how Klaus' tests signal errors.
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- Except for when that's how the test signals success: better notice
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that special address. (Look at the assembler listing output.)
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4. Run it on the tests. When you hit a failure or unimplemented opcode, write code until it works.
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Here are some references:
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- Detailed per-instruction timing, etc: http://www.masswerk.at/6502/6502_instruction_set.html
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- aaabbbcc-type breakdown: http://www.llx.com/~nparker/a2/opcodes.html
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- 6502 Hardware manual (KIM-1): http://users.telenet.be/kim1-6502/6502/hwman.html#AA
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- For doublechecking cycle counts: http://www.obelisk.demon.co.uk/6502/reference.html
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- Stack explanation (annoying writing): http://homepage.ntlworld.com/cyborgsystems/CS_Main/6502/6502.htm#STACK
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5. Some things will creep through. eg. https://github.com/zellyn/go6502/commit/a0cb814c9ed8eedfd558627be24934af6c257d32
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You'll find them later. :-)
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* 2013-02-27 - Tracking down "PP" instead of PRINT in Applesoft Basic
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Finally tracked it down to PLA of non-zero value not clearing the Z flag.
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Applesoft: D75D is a BNE that should always be taken, since GETCHR (D72C) does PLA of non-zero value.
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- Invaluable: Applesoft commented disassembly: http://www.txbobsc.com/scsc/scdocumentor/
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* 2013-03-07 - Speeding up visual.go
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Sped things up so that they take less than half as long as they did
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before. Replaced bitset.BitSet with direct array bitset to avoid
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checking for extensions, and to allow clearing by uint32.
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* Discrepancies
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My ZP,x and ZP,y were doing 16-bit adds, able to go outside the zero page.
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