pounder_test/src/adc.rs

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///! Stabilizer ADC management interface
///!
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///! # Design
///!
///! Stabilizer ADCs are connected to the MCU via a simplex, SPI-compatible interface. The ADCs
///! require a setup conversion time after asserting the CSn (convert) signal to generate the ADC
///! code from the sampled level. Once the setup time has elapsed, the ADC data is clocked out of
///! MISO. The internal setup time is managed by the SPI peripheral via a CSn setup time parameter
///! during SPI configuration, which allows offloading the management of the setup time to hardware.
///!
///! Because of the SPI-compatibility of the ADCs, a single SPI peripheral + DMA is used to automate
///! the collection of multiple ADC samples without requiring processing by the CPU, which reduces
///! overhead and provides the CPU with more time for processing-intensive tasks, like DSP.
///!
///! The automation of sample collection utilizes two DMA streams, the SPI peripheral, and a timer
///! compare channel for each ADC. The timer comparison channel is configured to generate a
///! comparison event every time the timer is equal to a specific value. Each comparison then
///! generates a DMA transfer event to write into the SPI TX buffer. Although the SPI is a simplex,
///! RX-only interface, it is configured in full-duplex mode and the TX pin is left disconnected.
///! This allows the SPI interface to periodically read a single word whenever a word is written to
///! the TX side. Thus, by running a continuous DMA transfer to periodically write a value into the
///! TX FIFO, we can schedule the regular collection of ADC samples in the SPI RX buffer.
///!
///! In order to collect the acquired ADC samples into a RAM buffer, a second DMA transfer is
///! configured to read from the SPI RX FIFO into RAM. The request for this transfer is connected to
///! the SPI RX data signal, so the SPI peripheral will request to move data into RAM whenever it is
///! available. When enough samples have been collected, a transfer-complete interrupt is generated
///! and the ADC samples are available for processing.
///!
///! The SPI peripheral internally has an 8- or 16-byte TX and RX FIFO, which corresponds to a 4- or
///! 8-sample buffer for incoming ADC samples. During the handling of the DMA transfer completion,
///! there is a small window where buffers are swapped over where it's possible that a sample could
///! be lost. In order to avoid this, the SPI RX FIFO is effectively used as a "sample overflow"
///! region and can buffer a number of samples until the next DMA transfer is configured. If a DMA
///! transfer is still not set in time, the SPI peripheral will generate an input-overrun interrupt.
///! This interrupt then serves as a means of detecting if samples have been lost, which will occur
///! whenever data processing takes longer than the collection period.
///!
///!
///! ## Starting Data Collection
///!
///! Because the DMA data collection is automated via timer count comparisons and DMA transfers, the
///! ADCs can be initialized and configured, but will not begin sampling the external ADCs until the
///! sampling timer is enabled. As such, the sampling timer should be enabled after all
///! initialization has completed and immediately before the embedded processing loop begins.
///!
///!
///! ## Batch Sizing
///!
///! The ADCs collect a group of N samples, which is referred to as a batch. The size of the batch
///! is configured by the user at compile-time to allow for a custom-tailored implementation. Larger
///! batch sizes generally provide for more processing time per sample, but come at the expense of
///! increased input -> output latency.
///!
///!
///! # Note
///!
///! While there are two ADCs, only a single ADC is configured to generate transfer-complete
///! interrupts. This is done because it is assumed that the ADCs will always be sampled
///! simultaneously. If only a single ADC is used, it must always be ADC0, as ADC1 will not generate
///! transfer-complete interrupts.
///!
///! There is a very small amount of latency between sampling of ADCs due to bus matrix priority. As
///! such, one of the ADCs will be sampled marginally earlier before the other because the DMA
///! requests are generated simultaneously. This can be avoided by providing a known offset to the
///! sample DMA requests, which can be completed by setting e.g. ADC0's comparison to a counter
///! value of 0 and ADC1's comparison to a counter value of 1.
///!
///! In this implementation, single buffer mode DMA transfers are used because the SPI RX FIFO can
///! be used as a means to both detect and buffer ADC samples during the buffer swap-over. Because
///! of this, double-buffered mode does not offer any advantages over single-buffered mode (unless
///! double-buffered mode offers less overhead when accessing data).
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use super::{
hal, sampling_timer, DMAReq, DmaConfig, MemoryToPeripheral,
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PeripheralToMemory, Priority, TargetAddress, Transfer, SAMPLE_BUFFER_SIZE,
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};
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// The following data is written by the timer ADC sample trigger into each of the SPI TXFIFOs. Note
// that because the SPI MOSI line is not connected, this data is dont-care. Data in AXI SRAM is not
// initialized on boot, so the contents are random.
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#[link_section = ".axisram.buffers"]
static mut SPI_START: [u16; 1] = [0x00];
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// The following global buffers are used for the ADC sample DMA transfers. Two buffers are used for
// each transfer in a ping-pong buffer configuration (one is being acquired while the other is being
// processed). Note that the contents of AXI SRAM is uninitialized, so the buffer contents on
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// startup are undefined. The dimensions are `ADC_BUF[adc_index][ping_pong_index][sample_index]`.
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#[link_section = ".axisram.buffers"]
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static mut ADC_BUF: [[[u16; SAMPLE_BUFFER_SIZE]; 2]; 2] =
[[[0; SAMPLE_BUFFER_SIZE]; 2]; 2];
macro_rules! adc_input {
($name:ident, $index:literal, $trigger_stream:ident, $data_stream:ident,
$spi:ident, $trigger_channel:ident, $dma_req:ident) => {
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/// $spi is used as a type for indicating a DMA transfer into the SPI TX FIFO
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/// whenever the tim2 update dma request occurs.
struct $spi {
_channel: sampling_timer::tim2::$trigger_channel,
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}
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impl $spi {
pub fn new(
_channel: sampling_timer::tim2::$trigger_channel,
) -> Self {
Self { _channel }
}
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}
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// Note(unsafe): This structure is only safe to instantiate once. The DMA request is hard-coded and
// may only be used if ownership of the timer2 $trigger_channel compare channel is assured, which is
// ensured by maintaining ownership of the channel.
unsafe impl TargetAddress<MemoryToPeripheral> for $spi {
/// SPI is configured to operate using 16-bit transfer words.
type MemSize = u16;
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/// SPI DMA requests are generated whenever TIM2 CHx ($dma_req) comparison occurs.
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const REQUEST_LINE: Option<u8> = Some(DMAReq::$dma_req as u8);
/// Whenever the DMA request occurs, it should write into SPI's TX FIFO to start a DMA
/// transfer.
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fn address(&self) -> usize {
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// Note(unsafe): It is assumed that SPI is owned by another DMA transfer and this DMA is
// only used for the transmit-half of DMA.
let regs = unsafe { &*hal::stm32::$spi::ptr() };
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&regs.txdr as *const _ as usize
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}
}
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/// Represents data associated with ADC.
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pub struct $name {
next_buffer: Option<&'static mut [u16; SAMPLE_BUFFER_SIZE]>,
transfer: Transfer<
hal::dma::dma::$data_stream<hal::stm32::DMA1>,
hal::spi::Spi<hal::stm32::$spi, hal::spi::Disabled, u16>,
PeripheralToMemory,
&'static mut [u16; SAMPLE_BUFFER_SIZE],
>,
_trigger_transfer: Transfer<
hal::dma::dma::$trigger_stream<hal::stm32::DMA1>,
$spi,
MemoryToPeripheral,
&'static mut [u16; 1],
>,
}
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impl $name {
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/// Construct the ADC input channel.
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///
/// # Args
/// * `spi` - The SPI interface used to communicate with the ADC.
/// * `trigger_stream` - The DMA stream used to trigger each ADC transfer by writing a word into
/// the SPI TX FIFO.
/// * `data_stream` - The DMA stream used to read samples received over SPI into a data buffer.
/// * `_trigger_channel` - The ADC sampling timer output compare channel for read triggers.
pub fn new(
spi: hal::spi::Spi<hal::stm32::$spi, hal::spi::Enabled, u16>,
trigger_stream: hal::dma::dma::$trigger_stream<
hal::stm32::DMA1,
>,
data_stream: hal::dma::dma::$data_stream<hal::stm32::DMA1>,
trigger_channel: sampling_timer::tim2::$trigger_channel,
) -> Self {
// Generate DMA events when an output compare of the timer hitting zero (timer roll over)
// occurs.
trigger_channel.listen_dma();
trigger_channel.to_output_compare(0);
// The trigger stream constantly writes to the TX FIFO using a static word (dont-care
// contents). Thus, neither the memory or peripheral address ever change. This is run in
// circular mode to be completed at every DMA request.
let trigger_config = DmaConfig::default()
.priority(Priority::High)
.circular_buffer(true);
// Construct the trigger stream to write from memory to the peripheral.
let mut trigger_transfer: Transfer<
_,
_,
MemoryToPeripheral,
_,
> = Transfer::init(
trigger_stream,
$spi::new(trigger_channel),
// Note(unsafe): Because this is a Memory->Peripheral transfer, this data is never
// actually modified. It technically only needs to be immutably borrowed, but the
// current HAL API only supports mutable borrows.
unsafe { &mut SPI_START },
None,
trigger_config,
);
// The data stream constantly reads from the SPI RX FIFO into a RAM buffer. The peripheral
// stalls reads of the SPI RX FIFO until data is available, so the DMA transfer completes
// after the requested number of samples have been collected. Note that only ADC1's (sic!)
// data stream is used to trigger a transfer completion interrupt.
let data_config = DmaConfig::default()
.memory_increment(true)
.transfer_complete_interrupt($index == 1)
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.priority(Priority::VeryHigh);
// A SPI peripheral error interrupt is used to determine if the RX FIFO overflows. This
// indicates that samples were dropped due to excessive processing time in the main
// application (e.g. a second DMA transfer completes before the first was done with
// processing). This is used as a flow control indicator to guarantee that no ADC samples
// are lost.
let mut spi = spi.disable();
spi.listen(hal::spi::Event::Error);
// The data transfer is always a transfer of data from the peripheral to a RAM buffer.
let mut data_transfer: Transfer<_, _, PeripheralToMemory, _> =
Transfer::init(
data_stream,
spi,
// Note(unsafe): The ADC_BUF[$index][0] is "owned" by this peripheral.
// It shall not be used anywhere else in the module.
unsafe { &mut ADC_BUF[$index][0] },
None,
data_config,
);
data_transfer.start(|spi| {
// Allow the SPI FIFOs to operate using only DMA data channels.
spi.enable_dma_rx();
spi.enable_dma_tx();
// Enable SPI and start it in infinite transaction mode.
spi.inner().cr1.modify(|_, w| w.spe().set_bit());
spi.inner().cr1.modify(|_, w| w.cstart().started());
});
trigger_transfer.start(|_| {});
Self {
// Note(unsafe): The ADC_BUF[$index][1] is "owned" by this peripheral. It shall not be used
// anywhere else in the module.
next_buffer: unsafe { Some(&mut ADC_BUF[$index][1]) },
transfer: data_transfer,
_trigger_transfer: trigger_transfer,
}
}
/// Obtain a buffer filled with ADC samples.
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///
/// # Returns
/// A reference to the underlying buffer that has been filled with ADC samples.
pub fn acquire_buffer(&mut self) -> &[u16; SAMPLE_BUFFER_SIZE] {
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// Wait for the transfer to fully complete before continuing.
// Note: If a device hangs up, check that this conditional is passing correctly, as there is
// no time-out checks here in the interest of execution speed.
while !self.transfer.get_transfer_complete_flag() {}
let next_buffer = self.next_buffer.take().unwrap();
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// Start the next transfer.
self.transfer.clear_interrupts();
let (prev_buffer, _) =
self.transfer.next_transfer(next_buffer).unwrap();
self.next_buffer.replace(prev_buffer); // .unwrap_none() https://github.com/rust-lang/rust/issues/62633
self.next_buffer.as_ref().unwrap()
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}
}
};
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}
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adc_input!(Adc0Input, 0, Stream0, Stream1, SPI2, Channel1, TIM2_CH1);
adc_input!(Adc1Input, 1, Stream2, Stream3, SPI3, Channel2, TIM2_CH2);