Game & Watch Bootloader is an application designed to allow easy installation/update of application on Game & Watch devices.
This allows updating Retro-Go simply by loading and running an update package from the SD card.
It is a major part of the Game & Watch Retro-Go SD project as it allows users to easily install or update Retro-Go SD
To install the bootloader on your Game & Watch, you need a JTAG adapter (such as an ST-Link v2).
You'll need the gnwmanager application to flash the bootloader onto your console.
git clone --recurse-submodules https://github.com/sylverb/game-and-watch-bootloader
make flash
GnWManager has official support for this firmware.
The following command will download the latest version of game-and-watch-bootloader and flash it:
gnwmanager flash-bootloader bank1 -- start bank1
Alternatively, you can manually download the latest released version here. Flash the binary to the internal flash of the Game & Watch using gnwmanager:
gnwmanager flash bank1 gnw_bootloader.bin -- start bank1
A diagnostic menu is available if you keep "PAUSE/SET" button pressed when turning on the Game & Watch.
Available information are :
- Bootloader version
- SD Card status : found or not, and SD mod type (SPI1 or OSPI1)
- Internal flash bank 2 status (valid or not)
- External flash model and size
If no button is pressed, bootloader will automatically run firmware updater or Retro-Go.
Currently, this bootloader is not compatible with dual boot (i.e., having both the original firmware and Retro-Go).
The flowchart for the application is the following :
graph TD
A[Start Bootloader] --> B[Detect SD Card]
B --> C{SD Card Found?}
C -->|Yes| D[Load Firmware Update File to RAM]
C -->|No| E[Boot Bank 2]
D --> F{File Loaded Successfully? /retro-go_update.bin}
F -->|Yes| G[Unmount SD Card and Deinit]
G --> H[Boot from RAM]
F -->|No| E
H --> I[Execute Firmware from RAM]
E --> J{Is Bank 2 Valid?}
J -->|Yes| K[Boot from Bank 2]
J -->|No| L[Wait 60 Seconds]
L --> M[Enter Deep Sleep]
K --> N[Execute Firmware from Bank 2]
/retro-go_update.bin must be an executable application built to run from RAM (@0x24000000). Two cases are handled:
- If the file is 1MB or smaller, it is loaded into RAM, and the bootloader starts the loaded application.
- If the file is larger than 1MB, its contents follow this structure:
| Application Binary (1024 KB) | Binary Length (4 Bytes) | Payload (Remaining) |
|---|
The advantage of this format is that it combines the firmware update application and the firmware binary into a single file, simplifying the update process for users.