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Modularizing CSMA + adding configuration options
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,111 @@ | ||
| use embedded_hal_async::delay::DelayNs; | ||
| use rand_core::RngCore; | ||
|
|
||
| use super::constants::*; | ||
| use super::user_configurable_constants::*; | ||
| use super::utils; | ||
|
|
||
| use crate::phy::config::TxConfig; | ||
| use crate::phy::driver::PacketBuffer; | ||
| use crate::phy::radio::futures::transmit; | ||
| use crate::phy::radio::Radio; | ||
| use crate::sync::channel::Sender; | ||
| use crate::sync::mutex::Mutex; | ||
| use crate::sync::mutex::MutexGuard; | ||
|
|
||
| #[cfg_attr(feature = "std", derive(Debug))] | ||
| #[cfg_attr(feature = "defmt", derive(defmt::Format))] | ||
| #[derive(PartialEq, Clone, Copy)] | ||
| pub enum TransmissionError { | ||
| CCAError, | ||
| } | ||
|
|
||
| pub async fn transmit_cca<'m, R, TIMER, Rng>( | ||
| radio: &'m Mutex<R>, | ||
| radio_guard: &mut Option<MutexGuard<'m, R>>, | ||
| wants_to_transmit_signal: &Sender<'_, ()>, | ||
| tx_frame: &PacketBuffer, | ||
| timer: &mut TIMER, | ||
| rng: &Mutex<Rng>, | ||
| mut backoff_strategy: CCABackoffStrategy<'_, Rng>, | ||
| ) -> Result<(), TransmissionError> | ||
| where | ||
| R: Radio, | ||
| TIMER: DelayNs, | ||
| Rng: RngCore, | ||
| { | ||
| let mut backoff_exponent = MAC_MIN_BE; | ||
| 'cca: for number_of_backoffs in 1..MAC_MAX_CSMA_BACKOFFS + 1 { | ||
| // try to transmit | ||
| let transmission_result = { | ||
| utils::acquire_lock(radio, wants_to_transmit_signal, radio_guard).await; | ||
| transmit( | ||
| &mut **radio_guard.as_mut().unwrap(), | ||
| &tx_frame.buffer, | ||
| TxConfig::default_with_cca(), | ||
| ) | ||
| .await | ||
| }; | ||
| if transmission_result { | ||
| break 'cca; // Send succesfully, now wait for ack | ||
| } | ||
|
|
||
| // As we are now going to wait a number of periods, release the | ||
| // mutex on the radio | ||
| *radio_guard = None; | ||
|
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| // CCA did not go succesfully | ||
| // Was this the last attempt? | ||
| if number_of_backoffs == MAC_MAX_CSMA_BACKOFFS { | ||
| return Err(TransmissionError::CCAError); // Fail transmission | ||
| } | ||
|
|
||
| backoff_strategy.perform_backoff(timer).await; | ||
| } | ||
|
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| Ok(()) | ||
| } | ||
|
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| pub enum CCABackoffStrategy<'r, Rng: RngCore> { | ||
| None, | ||
| ExponentialBackoff { | ||
| backoff_exponent: u16, | ||
| rng: &'r Mutex<Rng>, | ||
| }, | ||
| } | ||
|
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| impl<'r, Rng: RngCore> CCABackoffStrategy<'r, Rng> { | ||
| pub fn new_none() -> Self { | ||
| Self::None | ||
| } | ||
|
|
||
| pub fn new_exponential_backoff(rng: &'r Mutex<Rng>) -> Self { | ||
| Self::ExponentialBackoff { | ||
| backoff_exponent: MAC_MIN_BE, | ||
| rng, | ||
| } | ||
| } | ||
|
|
||
| pub async fn perform_backoff<TIMER: DelayNs>(&mut self, timer: &mut TIMER) { | ||
| match self { | ||
| Self::None => {} | ||
| Self::ExponentialBackoff { | ||
| backoff_exponent, | ||
| rng, | ||
| } => { | ||
| // Wait now for a random number of periods, before retrying | ||
| *backoff_exponent = core::cmp::min(*backoff_exponent + 1, MAC_MAX_BE); | ||
|
|
||
| // delay periods = random(2^{BE} - 1) periods | ||
| // Page 63 IEEE 802.15.4 2015 edition | ||
| let max_backoff = (1u32 << *backoff_exponent) - 1; | ||
| // The +1 in (max_backoff + 1) comes from the interpretation that the random() function | ||
| // used in the specification includes max_backoff as a possible value. The possible | ||
| // values periods now can take are: [0, max_backoff]. | ||
| let periods = rng.lock().await.next_u32() % (max_backoff + 1); | ||
| let delay = MAC_UNIT_BACKOFF_DURATION * periods as usize; | ||
| timer.delay_us(delay.as_us() as u32).await; | ||
| } | ||
| } | ||
| } | ||
| } |
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