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Version 1.01 - MEGA65 R3 microdrive reliability

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@dfernande132 dfernande132 released this 02 Sep 21:13
· 26 commits to master since this release
V1.01
b64cf0b

Version 1.01 - MEGA65 R3 microdrive reliability. V1.0's R3 build compiled clean but had never been tested on real R3 hardware. Since then, real-hardware testing across several MEGA65 R3 boards (with real, appreciated help from multiple testers, including the original author of this framework's HyperRAM controller) found an intermittent microdrive read issue ("bad or changed medium" on lrun/DIR) on some - not all - R3 units, traced to a real board-to-board timing margin difference in the physical HyperRAM chip's RWDS signal, not a logic bug.

What's new in this release:

  • R3's HyperRAM RWDS sampling delay is now tuned specifically for this board, found through an extensive empirical sweep across multiple R3 units - it fixes the issue on most of the affected boards tested so far (20+ consecutive successful loads plus a max-CPU-speed/max-RAM stress test on one previously-affected board, confirmed with no regression on boards that never showed the issue). It isn't a guaranteed fix on every single R3 unit - a small number may still be affected.
  • HyperRAM controller placement constraint (pblock) added to both R3 and R6 board files, matching the framework's own C64MEGA65 reference core - confirmed safe on real R3 and R6 hardware.
  • R6 is completely unaffected by this release - same behaviour as V1.0.
  • README now documents known issues honestly: this microdrive reliability note, and a separate pre-existing issue where VGA output (including the on-screen menu) doesn't currently work correctly - use HDMI, which works fine.

See INSTRUCTIONS.md (attached below) for exactly where each file goes on the SD card, and DECISIONES.md in the repository for the full investigation (multiple hypotheses tested and ruled out, the final fix, and why it isn't a 100% guarantee).

Included

  • QL4M65-CoreQL-V1.01_r6.cor - the compiled core for MEGA65 R6 (tested, unchanged behaviour from V1.0)
  • QL4M65-CoreQL-V1.01_r3.cor - the compiled core for MEGA65 R3 (tested on real hardware, see note above)
  • main.rom - Minerva 1.98, plain (no QL-SD driver - this core doesn't implement QL-SD yet, see PORTING-PLAN.md Milestone 4)
  • back.rom - Toolkit II (TK2)
  • blank.mdv - a blank, correctly-formatted microdrive test image (copy it twice under different names to test both drives at once)
  • INSTRUCTIONS.md - installation instructions

Minerva and TK2 are GPL/GNU-licensed and redistributed here on that basis. For other QL ROMs, see https://sinclairql.net/djw/qlrom/index.html.

Known limitations of this version: RAM tops out at 1024 KB (BRAM budget); VGA output doesn't currently work correctly (use HDMI); a small number of R3 units may still show occasional microdrive read issues even with this release's tuning; no mouse, no QL-SD hard-drive support yet. A physical reset button press or an abrupt power loss still doesn't run any firmware, so writes from the last moment before that can still be lost - the same accepted limitation other M2M cores with background write-back (C64MEGA65's vdrives, AExp's ADF floppy) share.

Thanks to everyone who tested builds on real R3 hardware during this investigation - this release exists because of that testing.

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