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D.1 CP/M Image Provenance

The system boots 64K CP/M 2.2: a Z80-optimised port of Burcon CP/M 2.2 with a custom BIOS for this board.

Original system

  • Source: Burcon CP/M 2.2 for the Altair 88-DCDD controller.
  • Reference image: src/cpm/cpm64_system.bin, the 5,632-byte CCP/BDOS region captured after the matching Burcon MOVCPM 64 and SYSGEN tools produced a bootable system in the Altair emulator.
  • Integrity: The image builder checks its SHA-256 fingerprint. This reference binary is preserved unchanged.
  • Original layout: CCP at 0xE300, BDOS at 0xEB00, and BIOS at 0xF900, with a 0x0700-byte BIOS reservation.

To regenerate the reference, use the matching Burcon utilities and MOVCPM instructions. The generator reports SAVE 38; preserve the BIOS reservation and verify relocated entry vectors.

CPM Customisations

  • Added the CLEAR command to clear the terminal screen.
  • Removed Ctrl+S flow control and printer support from CP/M.

Changes for this board

  • Z80 CP/M port: src/cpm/cpm64_z80.asm replaces the original CCP/BDOS at build time. Optimisations and removed features leave 246 bytes of padding (54 in CCP, 192 in BDOS) after adding CLEAR. Section sizes are unchanged; CCP and BDOS move upward by 0x0300. See the memory map for the running system's layout.
  • Custom BIOS: src/cpm/z80_bios.asm replaces the Altair BIOS and cold loader. It uses the board's Pico-serviced terminal and flash-disk ports, rather than the Altair controller's ports 0x08–0x0A. See Custom BIOS.
  • Non-standard 512 KiB disk format: each drive is a flat image of 128 tracks x 32 records x 128 bytes (524,288 bytes), with no sector framing or skew. It matches neither IBM 3740 SSSD nor the Altair 88-DCDD 77-track media. The BIOS reports one disk parameter block for A–D; see Disk format.
  • Validation: The port's unoptimised mode reproduces the reference byte-for-byte. Host tests check relocation and Z80 instructions, plus cold boot, DIR, program loading, and warm boot.
  • Audit details: src/cpm/cpm64_i8080.asm and src/cpm/cpm64_i8080_audit.md record the original disassembly and findings.

For supplied applications, DCC builds, and disk deployment, see Related projects.