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98 lines
2.3 KiB
Markdown
98 lines
2.3 KiB
Markdown
# The Hardware Abstraction Layer
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---
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## Building a driver
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* Writing to all those registers is tedious
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* You have to get the values right, and the order right
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* Can we wrap it up into a nicer, easier-to-use object?
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---
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## Typical driver interface
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```rust
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let p = pac::Peripherals.take().unwrap();
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let mut uarte0 = hal::uarte::Uarte::new(
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// Our singleton representing exclusive access to
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// the peripheral IP block
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p.UARTE0,
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// Some other settings we might need
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115200,
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hal::uarte::Parity::None,
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hal::uarte::Handshaking::None,
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);
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// Using the `uarte0` object:
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uarte0.write_all(b"Hey, I'm using a UART!").unwrap();
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```
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---
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## The Hardware Abstraction Layer
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* Contains all the drivers for a chip
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* Often common/shared across chip families
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* e.g. nRF52 HAL for 52832, 52840, etc
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* Usually community developed
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* Often quite different between MCU vendors
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* Different teams came up with different designs!
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---
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## Kinds of driver
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* PLL / Clock Configuration
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* Reset / Power Control of Peripherals
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* GPIO pins
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* UART
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* SPI
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* I²C
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* ADC
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* Timer/Counters
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* and more!
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---
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## Handling GPIO pins with code
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```rust
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// Get the singletons
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let p = pac::Peripherals.take().unwrap();
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// Make a driver for GPIO port P0
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let pins = hal::gpio::p0::Parts::new(p.P0);
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// Get Pin 13 on port P0 and make it an output
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let mut led_pin = pins.p0_13.into_push_pull_output(Level::High);
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// Now set the output low
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led_pin.set_low();
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```
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This differs widely across MCUs (ST, Nordic, Espressif, Atmel, etc). Some MCUs (e.g. Nordic) let you put any function on any pin, and some are much more restrictive!
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---
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## Correctness by design
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* HALs want to make it hard to do the wrong thing
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* Is a UART driver of any use, if you haven't configured at least one TX pin and one RX pin?
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* Should the UART driver check you've done that?
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---
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## Giving the pins to the driver
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```rust
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// 'degrade()' converts a P0_08 type into a generic Pin type.
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let pins = hal::uarte::Pins {
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rxd: pins.p0_08.degrade().into_floating_input(),
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txd: pins.p0_06.degrade().into_push_pull_output(Level::High),
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cts: None,
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rts: None,
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};
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let uarte = hal::uarte::Uarte::new(periph.UARTE1, pins, Parity::EXCLUDED, Baudrate::BAUD115200);
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```
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This is an example for the nRF52. We'll use it later in the example.
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