PC Engine CD BIOS Progress: Tested HuC6280 Routines and ADPCM DMA

Description and use

The "oss-pce-cd-bios" project has verified seven low‑level HuC6280 routines and demonstrated ADPCM DMA transfer in a real emulator core. Only one BIOS service (EX_GETVER) is callable; the rest remain stubs.

Problem

Developing a redistributable replacement for the PC Engine / TurboGrafx-CD System Card BIOS while ensuring low‑level routines and hardware paths are correctly implemented and verified in an actual emulator core.

Outcome

Seven low‑level HuC6280 routines are now verified in the real CPU core, ADPCM DMA transfer is demonstrated, and CD status/subcode‑Q responses are observed. However, only one BIOS API slot (EX_GETVER) is callable; the rest remain stubs, and core services like CD_RESET, CD_READ, CD_EXEC, and AD_TRANS are still unimplemented.

Workflow

• Build and run host‑side checks with make test
• Run real‑core integration tests with make test-real-core
• Optionally run standalone routine checks with make routine-real-core
• Verify ADPCM DMA transfer by issuing SCSI READ(6) and arming DMA via $180B
• Observe CD status and subcode‑Q responses for synthetic disc scenarios
• Validate arithmetic routine outputs against generated operand pairs and invariants
• Check 8 KiB of working RAM around synthetic ROM‑to‑RAM handoff for unexpected modifications

Evidence

Seven original routines exercised in the actual CPU core

Source

The real-core integration change records the seven-routine target; the division implementation is a concrete example

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A self-authored HuC6280 guest issues SCSI READ(6) through the emulated CD interface and arms ADPCM DMA via register $180B

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The default test workflow has also been clarified: make test, make test-real-core, make routine-real-core

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