Debrick

Intro

Built in firmware update function writes app (SYSTEM.VSB[0x100:]) to flash.

SYSTEM.VSB has 0x100 byte header, remaining 0x200000 is the application.

Secondary Bootloader (SBL) loaded to on-chip RAM at 0x80000000.

App loaded to external RAM at 0xc0000000.

Is it Bricked?

Boots to prompt

If it boots up to a prompt asking for update, it's not bricked.

Complete only Prepare SD Card step and reboot.

Device should flash back to factory firmware.

Screen lights up

If the screen lights up but boot does not complete, the secondary bootloader (SBL) is fine but the app is corrupt.

Complete all steps in RPi and OpenOCD section.

No visible response

If the screen does not light up, either SBL is corrupt or there is a hardware issue.

SBL may be corrupted when writing flash memory using ISP clip and FlashROM.

RPi and OpenOCD

Install and Setup

Install OpenOCD and connect RPi GPIO to e2 CPU JTAG Header (J9).

RPi / OpenOCD:

• https://iosoft.blog/2019/01/28/raspberry-pi-openocd
• https://learn.adafruit.com/programming-microcontrollers-using-openocd-on-raspberry-pi/overview

e2 J9:

• https://4.bp.blogspot.com/-kc4eZ1IID-k/VcfOYaU08aI/AAAAAAAAAqk/2kCErwdJcXc/s1600/IMG_9288.JPG

Config files:

• https://github.com/bangcorrupt/hacktribe/tree/master/openocd

Prepare SD Card

Prepare SD card with SYSTEM.VSB at correct path for device.

(Ensure SYSTEM.VSB is correct firmware for device as it was from the factory).

Factory Synth (e2, grey or blue):

KORG/electribe/System/SYSTEM.VSB

Factory Sampler (e2s, black or red):

KORG/'electribe sampler'/System/SYSTEM.VSB

Halt Processor

Halt processor in bootloader (0x80nnnnnn), before hand off to app (0xc0000000).

I haven't figured out resetting the CPU via JTAG. Halt in the bootloader before handing off to the app by pressing the power button at the same time as (or very slightly after) executing the openocd command. Processor will halt when openocd connects.

Output from openocd command will show the address halted at.

• If it begins with 0x8 we're in on-chip RAM in the bootloader (good).

• If it begins with 0xc we're in external RAM in the app (try again).

Connect to server

Connect to the telnet server provided by OpenOCD.

Set a breakpoint at 0xc0000000 and continue.

At breakpoint, load bytes from SYSTEM.VSB[0x100:] to 0xc0000000, then continue.

Write Firmware

Once booted, use built in firmware update function to write firmware to flash.

RPi and FlashROM

Couldn't get clean write using cheap connectors.

Test again using Pomona 5250.