Skip to content

DEBUG_AND_STATUS.md

Latest commit

 

History

History
185 lines (146 loc) · 5.25 KB

DEBUG_AND_STATUS.md

File metadata and controls

185 lines (146 loc) · 5.25 KB

Debug System and Project Status

Debug Flags

Debug output can be controlled via flags in 8080.c (lines 5-8):

#define DEBUG_CPU 0        // CPU instruction debugging (JNZ, DCR, etc.)
#define DEBUG_DISK_IO 0    // Disk I/O port operations
#define DEBUG_HALT 1       // Show registers when halting

Set to 1 to enable, 0 to disable.

DEBUG_CPU

Shows CPU instruction execution details:

  • [DCR B] 80 → 7F, zero flag=0 - Decrement operations
  • [JNZ] PC=0009, target=0007, zero=0, JUMPING to 0007 - Jump decisions

DEBUG_DISK_IO

Shows all disk I/O operations:

  • [OUT] Port 0x10: Select disk 0 - Port operations
  • [Disk] Write A: T0 S1 ← DMA 0x0200 - Disk read/write

DEBUG_HALT

Shows register dump when program halts:

========================================
HALT at PC=0x003F
========================================
Registers:
  A=FF  B=00  C=00  D=00  E=00  H=02  L=00
  SP=0000  PC=003F
Flags: AC Z P
========================================

ORG Directive Issue

Current Status: The emulator loads code at address 0x0000 regardless of the org directive.

Workaround: Use org 0h in assembly programs for this emulator.

Why: The codeload() function loads hex output sequentially starting at address 0. The assembler's org directive affects address calculations in the assembly, but not where the code is actually loaded.

Example:

org 0h          ; Correct for this emulator

; Fill buffer with test pattern
    lxi h, 0200h
    mvi b, 080h
    ...

Future Fix Options:

  1. Modify codeload() to parse and respect org directive
  2. Modify assembler to output position-independent code
  3. Add loader that reads org from assembly output

For now, always use org 0h for programs in this emulator.

What's Working

✅ Intel 8080 CPU Emulation

  • All instructions implemented
  • Flags (Zero, Sign, Parity, Carry, Aux Carry)
  • Interrupts (EI/DI, RST)
  • DAA (Decimal Adjust Accumulator)

✅ CP/M Console I/O

  • BDOS Functions: 1 (input), 2 (output), 9 (print string), 11 (status)
  • Port-based I/O: 0x00 (input), 0x01 (output)
  • Bidirectional buffering
  • Console output mirrored to Xcode debug console

✅ CP/M Disk Emulation

  • Two 256KB virtual disks (A: and B:)
  • 77 tracks × 26 sectors × 128 bytes per disk
  • BDOS Functions: 13 (reset), 14 (select), 25 (get current), 26 (set DMA)
  • Port-based I/O: 0x10-0x15
  • Read/Write/Home operations
  • Verified working with disk test program

✅ iOS Integration

  • UIKit-based emulator view with LED displays
  • Document browser for saving/loading programs
  • Assembler with hex output
  • Sample programs (Kill the Bit, Echo Test, Disk Test)

Next Steps

Near Term (Basic File Operations)

  1. Add BDOS file functions:

    • Function 15: Open File
    • Function 16: Close File
    • Function 20: Read Sequential
    • Function 21: Write Sequential
    • Function 22: Create File
    • Function 23: Rename File
    • Function 19: Delete File

  2. Implement CP/M directory structure:

    • Directory entries (32 bytes each)
    • File Control Blocks (FCB)
    • Allocation vectors
    • Directory hash/lookup

  3. Add file system operations:

    • Format disk with directory
    • Create/delete files
    • Read/write file data
    • Track allocation

Medium Term (Full CP/M)

  1. Load actual CP/M 2.2:

    • CCP (Console Command Processor)
    • BDOS (already partially implemented)
    • BIOS (needs implementation)

  2. Run CP/M programs:

    • Load .COM files
    • Execute ED, PIP, STAT, etc.
    • Support CP/M system calls

Long Term (Enhancements)

  1. Persistent disk images:

    • Save/load disk images to iOS filesystem
    • Import/export .DSK files
    • Pre-made disk images with software

  2. Enhanced UI:

    • Terminal view for console I/O
    • Disk browser/explorer
    • File manager
    • Keyboard input support

  3. Performance:

    • Optimize emulation speed
    • Adjustable CPU clock rate
    • Fast-forward mode

Test Results

Disk Test (Success: A=FF)

[Disk] Write A: T0 S1 ← DMA 0x0200
[Disk] Read A: T0 S1 → DMA 0x0200
HALT at PC=0x003F
Registers: A=FF

Program successfully:

  • Filled buffer with 0xAA pattern
  • Wrote 128 bytes to disk
  • Cleared buffer to 0x00
  • Read 128 bytes from disk
  • Verified data integrity (0xAA matched)
  • Halted with success code

Files Modified in This Session

  • 8080.c - Added disk emulation, BDOS functions, debug flags
  • 8080.h - Fixed CPU bugs, added aux carry, DAA, interrupts
  • EmulatorViewController.swift - Added console output polling
  • TextDocumentViewController.swift - Added disk test sample program
  • Document Browser-Bridging-Header.h - Added CP/M function declarations

Debug Tips

  1. Enable DEBUG_CPU to trace instruction execution
  2. Enable DEBUG_DISK_IO to see all disk operations
  3. DEBUG_HALT shows final state when program stops
  4. Watch Xcode console for all debug output
  5. Use STEP button to single-step through code (with DEBUG_CPU=1)

Current Limitations

  • ORG must be 0h (code loads at address 0x0000)
  • No file system yet (just raw sector I/O)
  • Console output only (no keyboard input UI yet)
  • STEP button steps by bytes not instructions (display issue)
  • Some printf output may not appear during fast execution

Congratulations on getting disk emulation working! 🎉