Fork of DirtyHairy/UnoCart-2600 (originally by Robin Edwards / electrotrains), adapted for the MCUDEV DevEBox STM32F407VGT6 board and its onboard microSD socket.
Upstream releases and history remain useful background; this tree is not drop-in compatible with the classic STM32F4 Discovery + breakout wiring.
- Primary target: MCUDEV DevEBox STM32F407VGT6 (8 MHz HSE, AMS1117 3.3 V regulator, onboard microSD via SDIO).
- Cartridge breakout wiring must match the remapped buses below (not the original Discovery PD=address / PE=data map).
To free PD2 for SDIO CMD (and avoid fighting the Atari address bus), the cart buses were moved:
| Bus | Original (Discovery) | This fork |
|---|---|---|
| Address A0–A12 | PD0–PD12 | PE0–PE12 |
| Data D0–D7 | PE8–PE15 | PD8–PD15 |
| Video mode straps | PC0 / PC1 | Unchanged (PC0=PAL60, PC1=PAL) |
Wiring checklist (Atari cart → MCU):
| Atari | MCU |
|---|---|
| A0–A12 | PE0–PE12 |
| D0–D7 | PD8–PD15 |
| +5V / GND | Board 5V input / GND (MCU runs at 3.3 V; level-shift or series resistors as in your breakout) |
GPIO details (cartridge_io.h, main.c in both Atari2600Cart and standalone):
SET_DATA_MODE_IN/SET_DATA_MODE_OUTonly change PD8–PD15 MODER bits so PD0–PD7 (including SDIO CMD on PD2) stay intact during cart emulation.DATA_OUT_SET()writes only the high byte of GPIOD ODR so SDIO pins are not cleared every bus cycle.
Upstream menu emulation waited for two identical ADDR_IN samples, then drove data only until the address changed exactly. On breadboard / long-wire setups that makes lower address bits noisy enough that the MCU rarely (or never) drives PD8–PD15, so the TV stays blank even when PE12 (A12) looks high.
This fork’s menu ROM path drives data for the whole A12-high window and updates the byte as the address changes (closer to a real cart OE). Menu commands (LDA $1E00,X to select item X) still require a few identical address samples so noisy A0–A7 do not open the wrong file. Implemented in cartridge_firmware.c (emulate_firmware_cartridge).
Game-cart drivers still use the older address-stability loops; if a title glitches after selection, the same A12-gated approach may need to be applied there.
Upstream used SPI (SPI2 on PB13/14/15, CS PB5). The DevEBox microSD is wired for SDIO, so FatFs now uses the SDIO driver:
| SD pin | MCU |
|---|---|
| D0 | PC8 |
| D1 | PC9 |
| D2 | PC10 |
| D3 | PC11 |
| CK | PC12 |
| CMD | PD2 |
Defines in source/STM32firmware/Atari2600Cart/src/defines.h:
FATFS_USE_SDIO 1FATFS_SDIO_4BIT 1
Makefile builds fatfs_sd_sdio.c plus stm32f4xx_sdio, stm32f4xx_dma, and misc (SPI SD path removed from the CLI build).
Init runs 1-bit then switches to 4-bit wide bus (falls back to 1-bit if wide-bus fails). Transfer clock defaults to ~8 MHz (SDIO_TRANSFER_CLK_DIV in defines.h) for reliability on the onboard socket; init stays ~400 kHz. disk_initialize and directory mounts retry a few times if the first attempt fails.
The DevEBox microSD card-detect pin is NC — FATFS_USE_DETECT_PIN is forced off so a floating PB6 is not mistaken for “no card.”
Internal pull-ups are enabled on D0–D3 and CMD. CK (PC12) is configured with no pull (host-driven clock).
System clock is HSI → PLL at 168 MHz (SDIOCLK 48 MHz via PLLQ). This avoids depending on the Discovery-oriented HSE setup; the DevEBox has an 8 MHz HSE, but this firmware does not require it for SYSCLK.
From source/STM32firmware/Atari2600Cart with an Arm GNU toolchain (arm-none-eabi-gcc, with newlib). A Darwin aarch64 toolchain may be unpacked under tools/ in this repo for local builds:
export PATH="/path/to/arm-none-eabi/bin:$PATH"
cd source/STM32firmware/Atari2600Cart
make clean
make bin hex # outputs in build/firmware.bin and build/firmware.hexFlash with ST-Link (make flash / st-flash) or DFU (BOOT0) as you prefer on the DevEBox.
- Not compatible with stock Discovery UnoCart breakouts without rewiring address/data to PE / PD8–15.
- Onboard DevEBox W25Q16 SPI flash and TFT header are unused by this firmware; they must not conflict with your cart wiring.
- Keep cart wiring short and grounded well; noisy A0–A11 was the main failure mode before the menu bus-timing change.
- SD card: FAT or FAT32, as upstream.
The remainder of this README is adapted from the original repository / DirtyHairy firmware tree.
The UnoCart-2600 is an open source SD-card multicart for the Atari 2600. Use the joystick or the SELECT/RESET keys to navigate the SD card and select a title to play.
SD card should be formatted as FAT or FAT32.
The UnoCart-2600 can emulate most banking schemes with ROM sizes up to 64k and RAM sizes up to 32k. (more description to follow)
The original UnoCart-2600 was based on Robin Edwards’ earlier UnoCart project for the Atari 8-bit. Upstream builds typically used an STM32F407 DISCOVERY board connected to a small PCB to breakout the Atari 2600 cartridge signals.
An article describing how to build an UnoCart for the Atari 8-bit was published in Excel Magazine issue #4. You can also get a PDF of the article here.
Building the cartridge for the 2600 is almost identical, with the same connections between D0-D7 and A0-A12, +5V and GND. All the other connections to the breakout PCB can be skipped, since these signals are not present on the 2600 cartridge slot.
Obviously, you'll need a breakout board designed for the 2600 cartridge slot rather than the Atari 8-bit. The design files for the breakout PCB are hosted here and can be used to make your own copy of the PCB.
This fork: use the DevEBox pin map in Changes in this fork above, not the Discovery pin map from the original article.
The UnoCart-2600 menu can be set to display in NTSC, PAL or PAL60 as follows:
- By default, the firmware will be NTSC.
- Connect PC0 -> GND for PAL60
- Connect PC1 -> GND for PAL
Note that this is for the menu only, and has no effect after you have selected a cartridge to play.
Robin Edwards also designed a custom PCB for the UnoCart-2600 pictured here. This is mainly to make it easier to get people to test the design. The PCB design files are not currently public.
The UnoCart-2600 firmware is open source under a GPL license. Upstream firmware updates: DirtyHairy releases.
- Design, hardware and firmware by Robin Edwards (electrotrains at atariage)
- Additional work on firmware by Christian Speckner (DirtyHairy at atariage)
- This fork: DevEBox STM32F407VGT6 port (SDIO microSD, remapped cart buses, A12-gated menu bus drive)