This time round, I’ll wrap up my coverage of the key ARMv6-M Thumb instructions and mnemonics that you can use to command the Raspberry Pi RP2040. There are not many instructions left that were not covered in parts one and two, and I won’t be including all the remaining mnemonics, only those you’re likely to use frequently.
Last time, I covered the basics of doing ARM assembly programming on the Raspberry Pi Pico’s RP2040 microcontroller. Now it’s time to get to grips with the dozens of instructions to which the RP2040’s Cortex-M0+ cores respond.
When I got my first microcomputer, I already knew Basic programming. My machine had a different Basic dialect from the one I’d learned at school, and there was a stack of graphics and sound functionality to get to grips with too, but it wasn’t long before I felt I’d mastered the high-level stuff and that it was time to move on to machine code. That’s how I’ve come to feel about the Raspberry Pi Pico’s RP2040 chip. The time’s right to learn ARM assembly programming on the Pico.
One of the reasons why an embedded application developer might choose to build their code on top of a real-time operating system like FreeRTOS is to emphasise the event-driven nature of the application. For “events” read data coming in on a serial link or from an I²C peripheral, or a signal to a GPIO from a sensor that a certain threshold has been exceeded. These events are typically announced by interrupting whatever job the host microcontroller is engaged upon, so interrupts are what I’ve chosen to examine next in my exploration of FreeRTOS on the Raspberry Pi RP2040 chip.