FC Lines

FC Lines (WIP)

This document describes the current Function Code (FC) line work. This is work-in-progress and needs testing. Please try it and report results.

Status

• FC shadow logging is available in the emulator.
• CPLD support is live; FC/BERR RTL is in rtl.fc/pistorm_fc.v (EPM240).

FC is treated as a full 3-bit value (0-7) end-to-end. The CPLD drives M68K_FC[2:0] and tri-states the lines when BGACK is asserted.

Enable FC (stub)

setvar enable_fc stub

This records FC transitions and logs them at verbose level without driving hardware.

Enable FC (CPLD mode)

setvar enable_fc cpld

This enables CPLD mode and will drive FC lines via the CPLD when the FC-capable bitstream is programmed.

BERR multiplexing on GPIO5

The FC/BERR CPLD bitstream multiplexes BERR onto GPIO5. To sample it:

• Load the kernel module with berr_reset_input=1 so GPIO5 is configured as input.
• Keep berr_reset_input=0 for legacy CPLD (GPIO5 is RESET output).

What we need from testers

• Confirm FC logging does not affect stability.
• Report any regressions or unexpected behavior.
• If you build the RTL bitstream, report whether FC pins behave as expected.