Flashing Microcontroller Firmware via SPI with the Bus Pirate

1. Introduction

This experiment demonstrates how to use the Bus Pirate to flash firmware to a microcontroller via SPI. This approach is useful for initial firmware upload, debugging, and updating microcontroller code in embedded systems.

2. Required Components

• Bus Pirate (v3.6 or later)
• Microcontroller with SPI programming capability (e.g., ATmega, PIC)
• Firmware file in binary (.bin) or hex (.hex) format
• Connecting wires or breadboard
• Computer with terminal software (e.g., PuTTY or Tera Term)

3. Wiring Setup

Connect the Bus Pirate to the microcontroller’s SPI programming pins:

• MOSI on the Bus Pirate to the microcontroller’s MOSI
• MISO on the Bus Pirate to the microcontroller’s MISO
• CLK on the Bus Pirate to the microcontroller’s SCK
• CS on the Bus Pirate to the microcontroller’s RESET or CS (depending on the microcontroller)
• GND on the Bus Pirate to the microcontroller’s GND

Power the microcontroller externally if required, as the Bus Pirate’s power may not suffice.

4. Entering SPI Mode on the Bus Pirate

In your terminal software, enter SPI mode by typing:

m 5

Follow the prompts to set up SPI mode:

• Clock Speed: Set to an appropriate level for your microcontroller (e.g., 1 MHz)
• Output Type: Choose normal (3.3V) or open drain, depending on your setup
• Pull-Up Resistors: Enable if required by your setup

5. Setting Up Firmware Flashing

Prepare the firmware file (.hex or .bin) and the flashing tool. Depending on your microcontroller, use a command-line tool such as avrdude (for ATmega) or pic32prog (for PIC32).

Example command (using avrdude for an ATmega):

avrdude -c buspirate -P /dev/ttyUSB0 -p m328p -U flash:w:firmware.hex:i

Replace /dev/ttyUSB0 with your Bus Pirate’s port and firmware.hex with the path to your firmware file.

6. Flashing the Firmware

Run the flashing command. The Bus Pirate will begin sending data over SPI to write the firmware to the microcontroller.

Observe the output in your terminal to verify successful communication and completion of the flash process. A successful flash will typically display a "Verification OK" or similar message.

7. Verifying Flash Success

After flashing, verify that the microcontroller runs the new firmware by testing its operation. You can also use the read command to check the flash contents:

avrdude -c buspirate -P /dev/ttyUSB0 -p m328p -U flash:r:verify.hex:i

Compare verify.hex with the original firmware to confirm a successful flash.

8. Troubleshooting Common Issues

• No Communication: Double-check wiring, especially the connections for MOSI, MISO, CLK, and CS.
• Flash Fails: Ensure your firmware file is correct and compatible with your microcontroller.
• Verification Fails: Confirm that the correct fuse settings are used (if applicable) and retry the flashing.

9. Conclusion

Flashing firmware over SPI with the Bus Pirate provides a versatile and accessible way to update or debug microcontrollers. With the proper setup, you can streamline the firmware flashing process in embedded projects.