Embedded Rust: A Primer on MMIO

Transcript

1. Embedded Rust A Primer on MMIO
2. Universal Machine Intelligence Embedded devices for automation. Firmware and tooling written in Rust. Doing more with less. Shipping March 2024.
3. Memory Mapped IO: Essential to Microcontrollers Memory Mapped I/O • How we interact with the real world • No special CPU instructions to control peripherals • Harvard architecture maximalism • General-purpose I/O and more advanced peripherals 0x0000 0000 Program Text 0x2000 0000 RAM 0x4000 0000 Peripherals 0x4000 0100 GPIO A 0x4000 0200 GPIO B
4. Anatomy of a Peripheral Register Source: st.com (RM0433)
5. Modifying Memory The C way GPIOA_ODR |= (1 << 5); GPIOA_ODR &= ~(1 << 5); The Rust way GPIOA.modify(|r,w| w .odr5() .set_bit() ); GPIOA.modify(|r,w| w .odr5() .clear_bit() ); // API generated by svd2rust
6. Modifying Memory The C way PWR_CR1 |= (1 << PWR_CSR1_PVDO); The Rust way PWR_CR1.modify(|r,w| w .pvdo() .set_bit() ); // Error: method `.pvdo()` does not exist for PWR_CR1
7. Modifying Memory: Real World Example The C way temp = GPIOA->OSPEEDR; temp &= ~(GPIO_OSPEEDER_OSPEEDR0 << (position * 2U)); temp |= (GPIO_Init->Speed << (position * 2U)); GPIOA->OSPEEDR = temp; The Rust way GPIOA.ospeedr.modify(|_, w| w .ospeedr0 .high_speed() );
8. Memory Ownership and MMIO How does the borrow checker work with MMIO? Bytes have a memory address… bits don’t. PhantomData to the rescue!
9. Memory Ownership and MMIO struct Foo<T> { _phantom: PhantomData<T> }
10. From Singletons to Partial Moves let peripherals = cortex_m::Peripherals::take().unwrap(); let gpioa = peripherals.GPIOA.split(...); let gpiob = peripherals.GPIOB.split(...); // Compile-time error! (GPIOB already moved) let gpiob = peripherals.GPIOB.split(...);
11. Typestate Programming // Pin<GPIOA, 5, Analog> ← Default state let led = gpioa.pa5; // Pin<GPIOA, 5, Output<PushPull>> let led = led.into_push_pull_output(); led.set_high(); // Pin<GPIOA, 5, Analog> let led = led.into_analog();
12. Type Erasure // Pin<GPIOA, 5, Input> let button = gpioa.pa5.into_input(); // ErasedPin<Input> let button = button.erase();
13. Team Arrow: Rust on the Road
14. teamarrow.com.au Team Arrow: Rust on the Road