///! Stabilizer DAC management interface ///! ///! # Design ///! ///! Stabilizer DACs are connected to the MCU via a simplex, SPI-compatible interface. Each DAC ///! accepts a 16-bit output code. ///! ///! In order to maximize CPU processing time, the DAC code updates are offloaded to hardware using ///! a timer compare channel, DMA stream, and the DAC SPI interface. ///! ///! The timer comparison channel is configured to generate a DMA request whenever the comparison ///! occurs. Thus, whenever a comparison happens, a single DAC code can be written to the output. By ///! configuring a DMA stream for a number of successive DAC codes, hardware can regularly update ///! the DAC without requiring the CPU. ///! ///! In order to ensure alignment between the ADC sample batches and DAC output code batches, a DAC ///! output batch is always exactly 3 batches after the ADC batch that generated it. ///! ///! The DMA transfer for the DAC output codes utilizes a double-buffer mode to avoid losing any ///! transfer events generated by the timer (for example, when 2 update cycles occur before the DMA ///! transfer completion is handled). In this mode, by the time DMA swaps buffers, there is always a valid buffer in the ///! "next-transfer" double-buffer location for the DMA transfer. Once a transfer completes, ///! software then has exactly one batch duration to fill the next buffer before its ///! transfer begins. If software does not meet this deadline, old data will be repeatedly generated ///! on the output and output will be shifted by one batch. ///! ///! ## Multiple Samples to Single DAC Codes ///! ///! For some applications, it may be desirable to generate a single DAC code from multiple ADC ///! samples. In order to maintain timing characteristics between ADC samples and DAC code outputs, ///! applications are required to generate one DAC code for each ADC sample. To accomodate mapping ///! multiple inputs to a single output, the output code can be repeated a number of times in the ///! output buffer corresponding with the number of input samples that were used to generate it. ///! ///! ///! # Note ///! ///! There is a very small amount of latency between updating the two DACs due to bus matrix ///! priority. As such, one of the DACs will be updated marginally earlier before the other because ///! the DMA requests are generated simultaneously. This can be avoided by providing a known offset ///! to other DMA requests, which can be completed by setting e.g. DAC0's comparison to a ///! counter value of 2 and DAC1's comparison to a counter value of 3. This will have the effect of ///! generating the DAC updates with a known latency of 1 timer tick to each other and prevent the ///! DMAs from racing for the bus. As implemented, the DMA channels utilize natural priority of the ///! DMA channels to arbitrate which transfer occurs first. ///! ///! ///! # Limitations ///! ///! While double-buffered mode is used for DMA to avoid lost DAC-update events, there is no check ///! for re-use of a previously provided DAC output buffer. It is assumed that the DMA request is ///! served promptly after the transfer completes. use stm32h7xx_hal as hal; use super::design_parameters::SAMPLE_BUFFER_SIZE; use super::timers; use hal::dma::{ dma::{DMAReq, DmaConfig}, traits::TargetAddress, MemoryToPeripheral, Transfer, }; // The following global buffers are used for the DAC code DMA transfers. Two buffers are used for // each transfer in a ping-pong buffer configuration (one is being prepared while the other is being // processed). Note that the contents of AXI SRAM is uninitialized, so the buffer contents on // startup are undefined. The dimensions are `ADC_BUF[adc_index][ping_pong_index][sample_index]`. #[link_section = ".axisram.buffers"] static mut DAC_BUF: [[[u16; SAMPLE_BUFFER_SIZE]; 3]; 2] = [[[0; SAMPLE_BUFFER_SIZE]; 3]; 2]; /// Custom type for referencing DAC output codes. /// The internal integer is the raw code written to the DAC output register. #[derive(Copy, Clone)] pub struct DacCode(pub u16); impl Into for DacCode { fn into(self) -> f32 { // The DAC output range in bipolar mode (including the external output op-amp) is +/- 4.096 // V with 16-bit resolution. The anti-aliasing filter has an additional gain of 2.5. let dac_volts_per_lsb = 4.096 * 2.5 / (1u16 << 15) as f32; (self.0 ^ 0x8000) as i16 as f32 * dac_volts_per_lsb } } impl From for DacCode { /// Encode signed 16-bit values into DAC offset binary for a bipolar output configuration. fn from(value: i16) -> Self { Self(value as u16 ^ 0x8000) } } macro_rules! dac_output { ($name:ident, $index:literal, $data_stream:ident, $spi:ident, $trigger_channel:ident, $dma_req:ident) => { /// $spi is used as a type for indicating a DMA transfer into the SPI TX FIFO struct $spi { spi: hal::spi::Spi, _channel: timers::tim2::$trigger_channel, } impl $spi { pub fn new( _channel: timers::tim2::$trigger_channel, spi: hal::spi::Spi, ) -> Self { Self { _channel, spi } } /// Start the SPI and begin operating in a DMA-driven transfer mode. pub fn start_dma(&mut self) { // Allow the SPI FIFOs to operate using only DMA data channels. self.spi.enable_dma_tx(); // Enable SPI and start it in infinite transaction mode. self.spi.inner().cr1.modify(|_, w| w.spe().set_bit()); self.spi.inner().cr1.modify(|_, w| w.cstart().started()); } } // Note(unsafe): This is safe because the DMA request line is logically owned by this module. // Additionally, the SPI is owned by this structure and is known to be configured for u16 word // sizes. unsafe impl TargetAddress for $spi { /// SPI is configured to operate using 16-bit transfer words. type MemSize = u16; /// SPI DMA requests are generated whenever TIM2 CHx ($dma_req) comparison occurs. const REQUEST_LINE: Option = Some(DMAReq::$dma_req as u8); /// Whenever the DMA request occurs, it should write into SPI's TX FIFO. fn address(&self) -> usize { &self.spi.inner().txdr as *const _ as usize } } /// Represents data associated with DAC. pub struct $name { next_buffer: Option<&'static mut [u16; SAMPLE_BUFFER_SIZE]>, // Note: SPI TX functionality may not be used from this structure to ensure safety with DMA. transfer: Transfer< hal::dma::dma::$data_stream, $spi, MemoryToPeripheral, &'static mut [u16; SAMPLE_BUFFER_SIZE], hal::dma::DBTransfer, >, } impl $name { /// Construct the DAC output channel. /// /// # Args /// * `spi` - The SPI interface used to communicate with the ADC. /// * `stream` - The DMA stream used to write DAC codes over SPI. /// * `trigger_channel` - The sampling timer output compare channel for update triggers. pub fn new( spi: hal::spi::Spi, stream: hal::dma::dma::$data_stream, trigger_channel: timers::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(4 + $index); // The stream constantly writes to the TX FIFO to write new update codes. let trigger_config = DmaConfig::default() .memory_increment(true) .double_buffer(true) .peripheral_increment(false); // Listen for any potential SPI error signals, which may indicate that we are not generating // update codes. let mut spi = spi.disable(); spi.listen(hal::spi::Event::Error); // AXISRAM is uninitialized. As such, we manually zero-initialize it here before // starting the transfer. // Note(unsafe): We currently own all DAC_BUF[index] buffers and are not using them // elsewhere, so it is safe to access them here. for buf in unsafe { DAC_BUF[$index].iter_mut() } { for byte in buf.iter_mut() { *byte = 0; } } // Construct the trigger stream to write from memory to the peripheral. let transfer: Transfer<_, _, MemoryToPeripheral, _, _> = Transfer::init( stream, $spi::new(trigger_channel, spi), // Note(unsafe): This buffer is only used once and provided for the DMA transfer. unsafe { &mut DAC_BUF[$index][0] }, // Note(unsafe): This buffer is only used once and provided for the DMA transfer. unsafe { Some(&mut DAC_BUF[$index][1]) }, trigger_config, ); Self { transfer, // Note(unsafe): This buffer is only used once and provided for the next DMA transfer. next_buffer: unsafe { Some(&mut DAC_BUF[$index][2]) }, } } pub fn start(&mut self) { self.transfer.start(|spi| spi.start_dma()); } /// Acquire the next output buffer to populate it with DAC codes. pub fn acquire_buffer(&mut self) -> &mut [u16; SAMPLE_BUFFER_SIZE] { // 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(); // Start the next transfer. let (prev_buffer, _, _) = self.transfer.next_transfer(next_buffer).unwrap(); // .unwrap_none() https://github.com/rust-lang/rust/issues/62633 self.next_buffer.replace(prev_buffer); self.next_buffer.as_mut().unwrap() } } }; } dac_output!(Dac0Output, 0, Stream6, SPI4, Channel3, TIM2_CH3); dac_output!(Dac1Output, 1, Stream7, SPI5, Channel4, TIM2_CH4);