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stm32/can: implement proper RX timestamps

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This commit is contained in:
chemicstry
2023-07-25 12:07:09 +03:00
parent 77e34c5e8a
commit 62ab0bf2e7
4 changed files with 58 additions and 16 deletions
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18
examples/stm32f4/src/bin/can.rs
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@ -10,6 +10,7 @@ use embassy_stm32::can::bxcan::{Fifo, Frame, StandardId};
use embassy_stm32::can::{Can, Rx0InterruptHandler, Rx1InterruptHandler, SceInterruptHandler, TxInterruptHandler};
use embassy_stm32::gpio::{Input, Pull};
use embassy_stm32::peripherals::CAN1;
use embassy_time::Instant;
use {defmt_rtt as _, panic_probe as _};
bind_interrupts!(struct Irqs {
@ -51,9 +52,22 @@ async fn main(_spawner: Spawner) {
let mut i: u8 = 0;
loop {
let tx_frame = Frame::new_data(unwrap!(StandardId::new(i as _)), [i]);
let tx_ts = Instant::now();
can.write(&tx_frame).await;
let (_, rx_frame) = can.read().await.unwrap();
info!("loopback frame {=u8}", unwrap!(rx_frame.data())[0]);
let envelope = can.read().await.unwrap();
// We can measure loopback latency by using receive timestamp in the `Envelope`.
// Our frame is ~55 bits long (exlcuding bit stuffing), so at 1mbps loopback delay is at least 55 us.
// When measured with `tick-hz-1_000_000` actual latency is 80~83 us, giving a combined hardware and software
// overhead of ~25 us. Note that CPU frequency can greatly affect the result.
let latency = envelope.ts.saturating_duration_since(tx_ts);
info!(
"loopback frame {=u8}, latency: {} us",
unwrap!(envelope.frame.data())[0],
latency.as_micros()
);
i += 1;
}
}