radare2/doc/gprobe.md

What is GProbe?

GProbe is a protocol to communicate with various parts from Genesis/STMicro/MegaChips that are mostly used in video chipsets.

These chips have an integrated Turbo186 core. With GProbe you can read and write RAM, reset the CPU, execute code in RAM, ... There is a proprietary Windows tool to do this, but radare2 offers much more functionality.

Gprobe got some public attention with the MonitorDarkly exploit.

What is implemented?

• Serial1 protocol wrapper
• DDC2Bi3 protocol wrapper (Linux only)
• RAM read-/write-access
• Reset
• DebugOn/DebugOff
• RunCode
• GetDeviceId
• GetInformation

TODOs

• DisplayPort AUX Channel protocol wrapper
• Flash commands

What is tested?

• building with sys/user.sh and sys/mingw32.sh on linux
• running radare2 on Linux and Windows
• communication via FTDI USB serial adaptor
• communication via DDC2Bi3
• controlling a MegaChips RD1-4320 DisplayPort 1.2a splitter reference board
• controlling a DELL U2410 connected via DVI

How to use for dummies?

radare2 -n -w gprobe:///dev/ttyUSB0

• "/dev/ttyUSB0" is the serial connection, use something like "COM3" on Windows
• "-n" is important to avoid an initial 32k read to identify the binary type
• "-w" if you want to allow writing to RAM

radare2 -n -w gprobe://i2c-4

• i2c-4 is the i2c bus where the GProbe device is connected
• find the appropriate bus with "ddcutil detect"
• make sure the i2c-dev kernel module is loaded

Setup for Turbo186 processor core:

• e asm.bits=16
• e asm.seggrn=8

Now enjoy all the great stuff that r2 offers, like:

• run grobe commands with =!?
• dump memory with px
• Visual mode with V, including cursor mode and insert hexpairs
• dumping segments to file
• disassembly and analysis