Adding precise control of timer periods and prescalers

This commit is contained in:
Ryan Summers 2020-12-08 14:25:46 +01:00
parent a134340726
commit 1a1d8fd8b9
2 changed files with 49 additions and 17 deletions

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@ -4,3 +4,6 @@ pub const ADC_SETUP_TIME: f32 = 220e-9;
/// The maximum DAC/ADC serial clock line frequency. This is a hardware limit. /// The maximum DAC/ADC serial clock line frequency. This is a hardware limit.
pub const ADC_DAC_SCK_MHZ_MAX: u32 = 50; pub const ADC_DAC_SCK_MHZ_MAX: u32 = 50;
/// The optimal counting frequency of the hardware timers used for timestamping and sampling.
pub const TIMER_FREQUENCY_MHZ: u32 = 100;

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@ -30,6 +30,8 @@ extern crate panic_halt;
#[macro_use] #[macro_use]
extern crate log; extern crate log;
use core::convert::TryInto;
// use core::sync::atomic::{AtomicU32, AtomicBool, Ordering}; // use core::sync::atomic::{AtomicU32, AtomicBool, Ordering};
use cortex_m_rt::exception; use cortex_m_rt::exception;
use rtic::cyccnt::{Instant, U32Ext}; use rtic::cyccnt::{Instant, U32Ext};
@ -54,11 +56,12 @@ use smoltcp::wire::Ipv4Address;
use heapless::{consts::*, String}; use heapless::{consts::*, String};
// The desired sampling frequency of the ADCs. // The number of ticks in the ADC sampling timer. The timer runs at 100MHz, so the step size is
const SAMPLE_FREQUENCY_KHZ: u32 = 500; // equal to 10ns per tick.
const ADC_SAMPLE_TICKS: u32 = 128;
// The desired ADC sample processing buffer size. // The desired ADC sample processing buffer size.
const SAMPLE_BUFFER_SIZE: usize = 1; const SAMPLE_BUFFER_SIZE: usize = 8;
// The number of cascaded IIR biquads per channel. Select 1 or 2! // The number of cascaded IIR biquads per channel. Select 1 or 2!
const IIR_CASCADE_LENGTH: usize = 1; const IIR_CASCADE_LENGTH: usize = 1;
@ -282,29 +285,51 @@ const APP: () = {
hal::dma::dma::StreamsTuple::new(dp.DMA1, ccdr.peripheral.DMA1); hal::dma::dma::StreamsTuple::new(dp.DMA1, ccdr.peripheral.DMA1);
// Configure timer 2 to trigger conversions for the ADC // Configure timer 2 to trigger conversions for the ADC
let timer2 = dp.TIM2.timer( let mut sampling_timer = {
SAMPLE_FREQUENCY_KHZ.khz(), // The timer frequency is manually adjusted below, so the 1KHz setting here is a
ccdr.peripheral.TIM2, // dont-care.
&ccdr.clocks, let mut timer2 =
); dp.TIM2.timer(1.khz(), ccdr.peripheral.TIM2, &ccdr.clocks);
// Configure the timer to count at the designed tick rate. We will manually set the
// period below.
timer2.pause();
timer2.set_tick_freq(design_parameters::TIMER_FREQUENCY_MHZ.mhz());
let mut sampling_timer = timers::SamplingTimer::new(timer2); let mut sampling_timer = timers::SamplingTimer::new(timer2);
sampling_timer.set_period(ADC_SAMPLE_TICKS - 1);
sampling_timer
};
let sampling_timer_channels = sampling_timer.channels(); let sampling_timer_channels = sampling_timer.channels();
let mut timestamp_timer = { let mut timestamp_timer = {
// The timer frequency is manually adjusted below, so the 1KHz setting here is a // The timer frequency is manually adjusted below, so the 1KHz setting here is a
// dont-care. // dont-care.
let timer5 = let mut timer5 =
dp.TIM5.timer(1.khz(), ccdr.peripheral.TIM5, &ccdr.clocks); dp.TIM5.timer(1.khz(), ccdr.peripheral.TIM5, &ccdr.clocks);
// Configure the timer to count at the designed tick rate. We will manually set the
// period below.
timer5.pause();
timer5.set_tick_freq(design_parameters::TIMER_FREQUENCY_MHZ.mhz());
// The time stamp timer must run at exactly a multiple of the sample timer based on the // The time stamp timer must run at exactly a multiple of the sample timer based on the
// batch size. To accomodate this, we manually set the period identical to the sample // batch size. To accomodate this, we manually set the period identical to the sample
// timer, but use a prescaler that is `BATCH_SIZE` longer. // timer, but use a prescaler that is `BATCH_SIZE` longer.
let mut timer = timers::TimestampTimer::new(timer5); let mut timer = timers::TimestampTimer::new(timer5);
timer.set_period(sampling_timer.get_period());
timer.set_prescaler( let period: u32 = {
sampling_timer.get_prescaler() * SAMPLE_BUFFER_SIZE as u16, let batch_duration: u64 =
); SAMPLE_BUFFER_SIZE as u64 * ADC_SAMPLE_TICKS as u64;
let batches_per_overflow: u64 =
(1u64 + u32::MAX as u64) / batch_duration;
let period: u64 = batch_duration * batches_per_overflow - 1u64;
period.try_into().unwrap()
};
timer.set_period(period);
timer timer
}; };
@ -667,9 +692,13 @@ const APP: () = {
); );
// Ensure that we have enough time for an IO-update every sample. // Ensure that we have enough time for an IO-update every sample.
assert!( let sample_frequency =
1.0 / (1000 * SAMPLE_FREQUENCY_KHZ) as f32 > 900_e-9 (design_parameters::TIMER_FREQUENCY_MHZ as f32
); * 1_000_000.0)
/ ADC_SAMPLE_TICKS as f32;
let sample_period = 1.0 / sample_frequency;
assert!(sample_period > 900_e-9);
hrtimer hrtimer
}; };