# Board Support Crates --- ## Using a 'normal' PC * Did you tell your PC it had a mouse plugged in? * Did you tell it what I/O address the video card was located at? * No! It auto-discovers all of these things. * USB, PCI-Express, SATA all have "plug-and-play" --- ## Using an Embedded System * Plug-and-play is extremely rare * Your MCU can put different functions (UART, SPI, etc) on different pins * The choice of which function goes on which pin was decided by the PCB designer * You now have to tell the software how the PCB was laid out * i.e UART0 TX is on Port 0, Pin 13 --- ## A Board Support Crate * You can wrap this up into a *Board Support Crate* * Especially useful if you are using a widely available dev-kit * e.g. the nRF52840-DK, or the STM32 Discovery * Still useful if the board design is an in-house one-off * Create the drivers and does the pin assignments for you * Helps make your application portable across different boards --- ## Using a Board Support Crate See `example-code/nrf52/bsp_demo` ```rust ignore [] #[entry] fn main() -> ! { let mut nrf52 = Board::take().unwrap(); loop { writeln!(nrf52.cdc, "On!").unwrap(); nrf52.leds.led_2.enable(); writeln!(nrf52.cdc, "Off!").unwrap(); nrf52.leds.led_2.disable(); } } ``` Note: We don't have to configure the LED pins as outputs. We don't have to configure the UART pins. The Board Support Crate did it all for us. --- ## Making a Board Support Crate ```rust ignore [] pub struct Board { /// The nRF52's pins which are not otherwise occupied on the nRF52840-DK pub pins: Pins, /// The nRF52840-DK UART which is wired to the virtual USB CDC port pub cdc: Uarte<nrf52::UARTE0>, /// The LEDs on the nRF52840-DK board pub leds: Leds, ... /// nRF52 peripheral: PWM0 pub PWM0: nrf52::PWM0, ... } impl Board { fn take() -> Option<Self> { todo!() } fn new(cp: CorePeripherals, p: Peripherals) -> Self { todo!() } } ``` Note: Because constructing the `Board` struct consumed *all* the peripherals from the PAC, it's important to re-export the ones the BSC didn't use so that applications can construct their own drivers using them,. --- ## More things to consider * Does the MCU start-up on a slow internal oscillator? * Are there jumpers to control routing on the board? * SD Cards: should you pick a driver, or let them choose? * Radios: same question!
