C64 MPS-802 Printer Audit

Core Workflow

Use this skill to audit whether EMULATORS models a Commodore MPS-802/1526 at the intended fidelity level.

1. Read references/mps802.md before making claims or edits.
2. Identify the intended behavior tier before judging correctness:
   • Basic text sink: validate printable character filtering, uppercase/lowercase mode, enhanced width, line buffering, formatter definition/use, diagnostic messages, and output file semantics.
   • PostScript glyph model: validate 8x8 glyph data, reverse mode, paging, programmable character, line/page geometry, formatter rendering, and required PSMPS802MatrixPrinter*.ps files.
   • Serial-printer peripheral: validate KERNAL-trap LISTEN/OPEN/CLOSE/SEND routing, device number behavior, secondary-address functions, and active-function lifetime.
   • Hardware/firmware model: only require 6504 CPU, RIOT/VIA, ROM, mechanical direction/timing, and bus timing if the implementation explicitly claims that tier.
3. Inspect local implementation paths first:
   • include/COMMODORE/SerialPrinterMPS802.hpp, src/COMMODORE/SerialPrinterMPS802.cpp
   • MPS802MatrixPrinterFormatter nested classes in the same files
   • include/CORE/MatrixPrinterEmulation.hpp, src/CORE/MatrixPrinterEmulation.cpp
   • include/COMMODORE/SerialPrinters.hpp, src/COMMODORE/SerialPrinters.cpp
   • include/COMMODORE/SerialIOPeripherals.hpp, src/COMMODORE/SerialIOPeripherals.cpp
   • include/COMMODORE/IOPBuilder.hpp, src/COMMODORE/IOPBuilder.cpp
   • include/C64/StdSerialPrinter.hpp, src/C64/StdSerialPrinter.cpp, and the VIC-20/C264 equivalents when host printer registration matters.
   • PSMPS802MatrixPrinterI.ps and PSMPS802MatrixPrinterII.ps copies under projects/, setups/, emulators/, and monitors/ when PostScript rendering is involved.
4. Compare against .codex/docs/MPS802.pdf first. Use the external URLs in references/mps802.md to verify historical/spec claims when internet access is available or when the user asks for web confirmation.
5. When changing C++ code, also use $emulators-framework-cpp-style.
6. When host-side C64 CIA2 IEC wiring, not just KERNAL traps, is involved, also use $c64-cia-audit.
7. Report whether each issue is a bug inside the current fidelity tier or a missing higher-fidelity feature.

Audit Priorities

Prioritize correctness in this order:

• Scope honesty: distinguish an output-file printer simulation from a firmware, timing, or mechanism-accurate MPS-802/1526.
• Device and channel behavior: default device 4, jumper-selectable device range in real hardware, secondary-address function selection, and active function reset on LISTEN/CLOSE.
• Secondary-address functions: 0x00 none, 0x01 use formatter, 0x02 define formatter, 0x03 set lines per page, 0x04 enable format/diagnostic messages, 0x05 define programmable character, 0x06 set line spacing, 0x07 business mode, 0x09 suppress diagnostic messages, and 0x0a reset.
• Formatter semantics: format-string parsing, text/space/numeric fields, 0x1d field separation while using a formatter, error strings such as *PE:F* and *.*, and whether errors are printed only when messages are enabled.
• Character sets and modes: PETSCII to printer-code handling, business mode, graphics/default mode, 8x8 glyph data, enhanced-width enable/disable, uppercase/lowercase control, reverse field, paging on/off, and programmable character use at code 0xfe.
• Page geometry: 80 columns, 640 horizontal dot positions, 8 vertical dots, 6 LPI text, 9 LPI graphics, 66 lines on 11-inch paper, paper border handling, and PostScript scale constants. Treat any code comment/manual mismatch as an audit target.
• Basic vs PostScript parity: document behavior implemented only in MPS802PostscriptMatrixPrinterEmulation, especially paging, programmable character, and line/page features.
• Compatibility limits: do not require 6504 firmware execution, 6532/6522 register behavior, ROM execution, bidirectional head timing, or serial-bus electrical timing unless the implementation claims those features.

Validation Hints

Prefer focused probes:

• BASIC/KERNAL snippets that OPEN the printer on device 4, choose secondary addresses 0, 1, 2, 4, 7, 9, and 10, send data, and CLOSE the channel.
• Byte streams that exercise enhanced width, disable enhanced width, reverse on/off, paging on/off, uppercase/lowercase, formatter definition/use, and reset.
• Output-file assertions for basic mode and PostScript token checks for glyph definitions, formatter output, programmable character bytes, page breaks, drawByteBits, and missing template-file logging.
• Tests that separate serial-routing failures from matrix-printer rendering or formatter failures.