PicoFlashButton

This project involves using assembly and C code to create an alarm interrupt that periodically flashes an LED on a Raspberry Pi Pico board, with additional functionality for button presses to modify the flashing rate and state.

Summary

This Github repository contains the source code and documentation for a project that uses ARM assembly and C code to control the LED built into a Raspberry Pi Pico. The LED flashes every second, alternating between on and off.

The project includes an interrupt service routine to handle button presses on the MAKER-PI-PICO board. Pressing button GP21 stops and starts the flashing behavior, while pressing GP20 or GP22 adjusts the flashing rate. The current interval value and LED flashing state are stored in shared data segments.

The project is written entirely in ARM assembly, with C header-files and wrapper functions.

To compile the assembly code, you can use the following commands:

arm-none-eabi-as -o gpio.o gpio.S
arm-none-eabi-as -o alarm.o alarm.S
arm-none-eabi-as -o button.o button.S
arm-none-eabi-as -o pico.o pico.S

The pico.ld file includes the memory layout of the Raspberry Pi Pico and specifies the entry point for your program, while gpio.ld, button.ld, and alarm.ld files specify the memory regions for the code and data sections for their respective functions. By using all of these linker scripts together, you it ensures that the code and data sections are properly located in memory and that the entry point is correctly defined.

To link all of your object files, you would use a command similar to:

arm-none-eabi-ld -T pico.ld -T gpio.ld -T button.ld -T alarm.ld -o picoflashbutton.elf pico_asm.o gpio.o button.o alarm.o

Then to convert the picoflashbutton.elf file into a binary file format (picoflashbutton.bin). The -O option specifies the output format, and binary is the output format being used:

arm-none-eabi-objcopy -O binary picoflashbutton.elf picoflashbutton.bin

To use picoprobe with picoflashbutton.bin, you can follow these steps:

1. Connect your Raspberry Pi Pico to your computer using a USB cable.

2. Install the picoprobe software on your computer by following the instructions provided on the official Raspberry Pi Pico documentation.

3. Connect the picoprobe to your Raspberry Pi Pico by connecting the GND, SWDIO, and SWCLK pins of the picoprobe to the corresponding pins on the Raspberry Pi Pico.

4. Open a terminal window and navigate to the directory where the picoflashbutton.bin file is located.

5. Use the picoprobe tool to flash the binary file to the Raspberry Pi Pico by running the following command:

picoprobe load picoflashbutton.bin

6. Once the binary file is loaded onto the Raspberry Pi Pico, you can reset the board by pressing the reset button on the board or by running the following command in the terminal:

picoprobe reset

7. The program should now be running on the Raspberry Pi Pico, and you can interact with it using the button connected to GP21.