May 28, 2026

Contents Hardware Identifying and soldering the connectors

Testing the UART

JTAG

Software Configuring OpenOCD

Dumping the address space

Firmware disassembly and analysis

Relinking the firmware

Patching the firmware

More firmware analysis

Making my changes Buttons

LEDs

Building an API

My code

Fixing bypass gain

Flashing the new firmware

Firmware update format

Applying the update

Future directions MIDI 2 property exchange

Custom DSP effects

Combined “mega-firmware”

Overall thoughts

I’m having a lot of fun with reverse engineering lately, so when I was looking over the service manual for my guitar amp, a Yamaha THR10c, and saw references to a UART header in the schematic, I got excited. I wondered if anything cool was hiding in there. Next to it was a JTAG header.…