UMDv2

The Universal Mega Dumper v2 project aims to be a complete open-sourced solution for cartridge dumping and writing. It includes a very performant MCU which has a direct memory connection to a generalized databus consisting of 24 address bits and 16 data lines. Along with a dozen or so control signals, it should be sufficient to interface with most cartridge types.

Hardware

This firmware is designed to run on UMDv2 hardware.

Tools

IDE

This project is developped using ST's STM32CubeIDE which is an Eclipse-based IDE available for free on all major platforms (Debian, MacOS, Winblows).

Programmer

An ST-LINK/V2 JTAG programmer is required to debug and develop firmware.

Communication Protocol

The UMDv2 enumerates over USB as a VCP (Virtual COM Port) which means it is easy to talk to the UMDv2 via any OS since COM ports are standard everywhere.

CRC32/MPEG-2

Packets sent to the UMDv2 include a CRC32/MPEG-2 checksum. This CRC was chosen simply because the STM32 MCU used has built-in hardware which calculates this CRC very quickly. This online resource https://crccalc.com/ can be used to verify CRC32/MPEG-2 calculations.

Send Commands / Data

When sending commands and data to the UMDv2, this format must be followed. Note that data is interpreted in little endian.

2 bytes - Command Word
2 bytes - Payload Size
4 bytes - CRC32/MPEG-2 (calculated on entire packet, but skip these 4 bytes obviously)
Payload (Payload size bytes)
- Payload can be 0 to 4K bytes

UMDv2 Replies

The UMDv2 replies to commands in a specific structure similar to the sending format except that it omits the CRC32/MPEG-2 calculation. Receive data will follow this format:

2 bytes - Command acknowledge (same 2 bytes as command which is being acknowledge, error codes are also possible)
2 bytes - Payload Size
Payload (Payload size bytes)
- Payload can be 0 to 4K bytes

Example 1

This byte sequence is transmitted to the UMDv2:

0x02 0x00 0x04 0x00 0x4C 0x51 0x8F 0x57 0x0F 0x00 0x00 0x00

0x0002 = Command
0x0004 = Payload size
0x578F514C = CRC32/MPEG-2
- calculated on 0x02 0x00 0x04 0x00 0x0F 0x00 0x00 0x00
0x0F 0x00 0x00 0x00 = Payload

The UMDv2 will respond will the following sequence:

0x02 0x00 0x00 0x00

0x0002 = Command being acknowleged
0x0000 - Payload size

Example 2 - no payload