5.0.0 — August 2026

5.0.0 — August 2026

The first release on the GCU Gen 3 — a development cycle's worth of shift-smarts, logged and tagged so the box tells you what it did. The GCU Gen 3 now drives the brake light, every auto-downshift refusal is explained in the logs, and shift traces record exactly where the shift drum went.

Install instructions: GCU Gen 3 — Flashing Firmware

This is a CAN (Gen2, drive-by-wire) build only — the zip contains no KLine firmware. The GCU Gen 3 will support KLine cars, but that path isn't out yet.

What's in this release

• The GCU drives the brake light. Brake pressure from the dash's brake channels switches the brake light on and off. Failsafe is fail-bright: if the dash goes quiet or a sensor reads out of range, the light comes on rather than staying dark. A bench mode (BRAKE_TEST) lets you force the light on for wiring checks.
• Auto-downshift refusals are visible. Hold the down paddle and the box walks down toward redline. Every time it declines a shift — revs still climbing, wrong conditions, no fresh data — it now says why, in the logs and on the dash. No more silent "hold did nothing."
• Shift logs tell the truth. Every upshift records where the drum actually went (not just "it shifted"), shift success/fail counters are readable without a dash, and twice as many shift traces survive an outing.
• Settings saves no longer lie. A failed write to flash now reports failure instead of saying OK.
• Gentler neutral finder. The progressive neutral pulse is configurable (5/10/20/30/40 ms) instead of one fixed value.
• Flasher improvements. It enters the bootloader on its own before flashing, and the Sessions viewer got a proper dialog and scroll-pause.

Flasher note

This release contains .bin files for the Feather-M4-based GCU Gen 3. The GCU Gen 3 flasher is built into the same app; connect via the USB-C piggyback on the harness (dealer-installed if your car doesn't have it), power the car on first, and pick release_CAN_feather-5.0.0.bin.

Downloads

• Rush SR — GCU Firmware Releases (this repo): rush_GCU_5.0.0.zip below.

Install instructions

See the owner's manual — GCU Gen 3 for full flashing, telemetry, log-pulling, and troubleshooting steps.

3.1.1 — July 2026

3.1.1 — July 2026

You can set the compressor cut-in and cut-out pressures yourself now. They still ship at 70 and 90 PSI, so nothing changes unless you change it.

• Set it from the flasher: the Compressor row shows the band the GCU is running. Change the numbers, click Save, and it stores them. The setting survives a power cycle and a reflash.
• Bad numbers get refused: cut-in has to be 50 PSI or higher, cut-out 130 or lower, and cut-out at least 10 PSI above cut-in.
• Only before you've shifted: saving briefly stops the GCU watching the paddles, so it only allows the write before the first shift after power-on. Set the band in the paddock.
• Shift timing doesn't follow the band: shift length still tracks actual tank pressure. Moving the band changes when the compressor runs, nothing else.

Install instructions: Legacy GCU — Updating the Legacy GCU

This is a Legacy GCU release (.hex files, USB-B flashing). If your car has the Active GCU, you want the 5.x releases instead.

3.1.0 — March 2026

3.1.0 — March 2026

Much faster sequential shifting. Each shift now completes in about 180ms (previously 325ms), allowing approximately 5.5 shifts per second instead of 3. You'll notice the difference on fast downshift sequences.

• Faster shifts: Reduced the wait time between shifts by over 70%. The air cylinder returns fast enough that the old delays were unnecessary.

3.0.6

3.0.6 — October 2025

Shifts adapt to tank pressure. The GCU now automatically adjusts shift timing based on how much air is in the tank.

• At low tank pressure, shifts take a bit longer to make sure they complete reliably.
• At normal pressure (70–90 PSI), shifts behave as before.
• At high pressure, shifts are quicker since there's more force available.

You don't need to do anything — this happens automatically. The result is more consistent shifts regardless of tank pressure.

3.0.5

3.0.5 — June 2025

Diagnostic LED improvements.

• Startup self-test: When the GCU powers on, the red, yellow, and green LEDs light up in sequence. This confirms all three LEDs are working.
• Compressor indicator: The yellow LED now flashes while the air compressor is running. Useful for confirming the compressor is cycling on and off correctly — if you suspect a compressor issue, watch the yellow LED.

3.0.4

3.0.4 — June 2025

First stable release with countershift. Countershift sends a brief reverse air pulse after each shift to help the gear fully seat, reducing the chance of a missed or incomplete shift.

• Separate shift timing for upshifts and downshifts
• Improved shift light behavior