3.3 KiB
Write the Uarte implementation
Step-by-Step Solution
Check Documentation.
The UART protocol requires four pins, they are usually labelled:
- RXD
- TXD
- CTS
- RTS
Check the documentation to find out which pins are reserved for these and what their configuration needs to be.
Explore the nrf-hal
to find out what needs to be done.
The nrf52840-hal
is a crate that exports all the 52840
flagged features from the nrf-hal-common
. Let's take a look at the Uarte module.
In line 16 we see, that the nRF52840 uses the hal::pac::UARTE1
peripheral.
In line 44 you find the struct Uarte<T>(T)
, the interface to a UARTE instance T
. Besides the instance T
, the instantiating method takes variables of the following types as arguments: Pins
, Parity
and Baudrate
.
A quick search of the document reveals where to find all of them:
Pins
: Line 463Parity
andBaudrate
: Re-export on line 34
Add the following lines as import:
use hal::pac::uarte0::{
baudrate::BAUDRATE_A as Baudrate, config::PARITY_A as Parity};
use hal::uarte;
Add struct Uarte
that serves as a wrapper for the UARTE1
instance.
The struct has one field labelled inner
, it contains the UARTE1
instance.
Bring up the peripheral in the fn init()
Take a closer look at the definition of the Pins
struct. Import the types of the pin configuration that you don't have yet. Note that the third and fourth pin are each wrapped in an Option
.
Level?
Create an instance of this struct in fn init()
with the appropriate pins and configurations.
Create an interface to the UARTE1 instance with uarte::Uarte::new(...)
. The UARTE0 instance can be found in the periph
variable. Set parity to INCLUDED
and the baud rate to BAUD115200
.
Board struct
Add a field for the Uarte
struct in the Board struct.
add the field to the instance of the Board struct in fn init()
.
Implementing the fmt::Write
trait
We can't just write to the Uarte instance. A simple write would write from flash memory. This does not work because of EasyDMA. We have to write a function that implements the fmt::Write
trait. This trait guarantees that the buffer is fully and successfully written on a stack allocated buffer, before it returns.
What exactly does the trait guarantee?
Create a public method write_str
. It takes a mutable reference to self and a &str
as argument. It returns an fmt::Result
Create a buffer. The type is an array of 16 u8, set to all 0.
To copy all data into an on-stack buffer, iterate over every chunk of the string to copy it into the buffer:
for block in string.as_bytes().chunks(16) {
buf[..block.len()].copy_from_slice(block);
self.inner.write(&buf[..block.len()]).map_err(|_| fmt::Error)?;
}
return Ok(())
Connect your computer to the virtual UART
Use the following command to find the address of the nRF52840-DK on your computer.
ls /dev/tty*
Run the following command to run screen
with the nRF52840-DK with 115200 baud.
screen <adress of mc> 115200
Run the example.
In another terminal window go into the folder down-the-stack/apps
.
Use the following command.
cargo run --bin uarte_print
On your terminal window where screen
runs, "Hello, World" should appear.