Soft & hard reset loses local disc info

[mattgodbolt]

If you've picked a local disc and then do a soft or hard reset, you lose the disc image as the reset code reloads the FDC module, losing the disc.

(Reported via Chris Jordan)

[mattgodbolt]

@claude what steps would we need in order to fix this issue?

[claude]

Claude finished @mattgodbolt's task —— View job

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Analysis Complete: Reset/Disc Issue Solution

I've analyzed the codebase to understand how resets work and why local disc info is lost. Here are the steps needed to fix this issue.

Todo List:

• Understand the current reset implementation (soft/hard reset)
• Analyze FDC module and disc loading mechanism
• Identify where disc state is lost during reset
• Propose solution steps to preserve disc state

Root Cause Analysis

The Issue:

1. Initial Disc Loading: When the emulator starts, discs are loaded via discImage/secondDiscImage variables from URL params (src/main.js:1286-1302)
2. Local Disc State: When users pick a local disc, it updates parsedQuery.disc1 and calls loadDiscImage() to load into the FDC (src/main.js:1162-1164)
3. Reset Problem: During reset (src/6502.js:1171), this.fdc.powerOnReset() is called for hard reset and this.fdc.reset() for soft reset, which completely reinitializes the FDC module but doesn't reload any disc images

Key Files Involved:

• src/6502.js:1131 - Reset function that calls FDC reset
• src/intel-fdc.js:350 - powerOnReset() clears drive state
• src/intel-fdc.js:361 - reset() deselects drives
• src/main.js:1286-1302 - Initial disc loading only happens at startup
• src/main.js:703-707 - setDisc1Image() updates parsedQuery.disc1 for user-selected discs

Solution Steps Required

To fix this issue, here's what needs to be implemented:

Step 1: Add Disc State Storage to 6502 CPU

• Modify src/6502.js to track currently loaded discs
• Add properties to store disc references for drives 0 and 1
• Update these references whenever discs are loaded

Step 2: Modify Reset Logic

• In Cpu6502.reset() method (src/6502.js:1131):
  • Before calling fdc.powerOnReset()/fdc.reset(), save current disc state
  • After FDC reset, automatically reload any previously loaded discs
  • Ensure this works for both hard and soft resets

Step 3: Enhance Disc Loading Integration

• Update loadDiscImage() in src/main.js to notify the CPU about loaded discs
• Ensure both startup discs and user-selected discs are tracked
• Handle edge cases like disc ejection/swapping

Step 4: Testing

• Test with local discs created via browser storage
• Test with URL-provided disc images
• Verify both soft reset (Ctrl+Break) and hard reset preserve disc state
• Ensure disc modifications are preserved through resets

Implementation Files to Modify:

1. src/6502.js - Add disc state tracking and modify reset logic
2. src/main.js - Update disc loading to register with CPU
3. src/intel-fdc.js - Potentially add helper methods for disc state queries
4. Tests - Add test cases for reset behavior with loaded discs

This solution would ensure that soft/hard resets maintain the user's disc selection, completely fixing the reported issue.

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[mattgodbolt]

Per #517 (and tested manually) this bug is actually no longer present.