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firmware: optimize dma_record_output.
This removes a number of bounds checks and adds a fast path for outputting exactly one word to DMA, which is the most common operation.
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bdd18de2c1
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@ -1,5 +1,5 @@
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#![feature(lang_items, asm, panic_unwind, libc, unwind_attributes,
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panic_implementation, panic_info_message)]
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panic_implementation, panic_info_message, nll)]
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#![no_std]
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extern crate libc;
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@ -300,19 +300,24 @@ extern fn dma_record_stop(duration: i64) {
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}
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#[unwind(aborts)]
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extern fn dma_record_output(timestamp: i64, channel: i32, address: i32, word: i32) {
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dma_record_output_wide(timestamp, channel, address, [word].as_c_slice())
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}
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#[unwind(aborts)]
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extern fn dma_record_output_wide(timestamp: i64, channel: i32, address: i32, words: CSlice<i32>) {
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assert!(words.len() <= 16); // enforce the hardware limit
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#[inline(always)]
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unsafe fn dma_record_output_prepare(timestamp: i64, channel: i32, address: i32,
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words: usize) -> &'static mut [u8] {
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// See gateware/rtio/dma.py.
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let header_length = /*length*/1 + /*channel*/3 + /*timestamp*/8 + /*address*/2;
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let length = header_length + /*data*/words.len() * 4;
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const HEADER_LENGTH: usize = /*length*/1 + /*channel*/3 + /*timestamp*/8 + /*address*/2;
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let length = HEADER_LENGTH + /*data*/words * 4;
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let header = [
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if DMA_RECORDER.buffer.len() - DMA_RECORDER.data_len < length {
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dma_record_flush()
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}
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let record = &mut DMA_RECORDER.buffer[DMA_RECORDER.data_len..
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DMA_RECORDER.data_len + length];
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DMA_RECORDER.data_len += length;
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let (header, data) = record.split_at_mut(HEADER_LENGTH);
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header.copy_from_slice(&[
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(length >> 0) as u8,
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(channel >> 0) as u8,
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(channel >> 8) as u8,
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@ -327,29 +332,39 @@ extern fn dma_record_output_wide(timestamp: i64, channel: i32, address: i32, wor
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(timestamp >> 56) as u8,
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(address >> 0) as u8,
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(address >> 8) as u8,
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];
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]);
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let mut data = [0; 16 * 4];
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for (i, &word) in words.as_ref().iter().enumerate() {
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let part = [
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data
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}
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#[unwind(aborts)]
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extern fn dma_record_output(timestamp: i64, channel: i32, address: i32, word: i32) {
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unsafe {
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let data = dma_record_output_prepare(timestamp, channel, address, 1);
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data.copy_from_slice(&[
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(word >> 0) as u8,
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(word >> 8) as u8,
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(word >> 16) as u8,
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(word >> 24) as u8,
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];
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data[i * 4..(i + 1) * 4].copy_from_slice(&part[..]);
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]);
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}
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let data = &data[..words.len() * 4];
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}
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#[unwind(aborts)]
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extern fn dma_record_output_wide(timestamp: i64, channel: i32, address: i32, words: CSlice<i32>) {
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assert!(words.len() <= 16); // enforce the hardware limit
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unsafe {
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if DMA_RECORDER.buffer.len() - DMA_RECORDER.data_len < length {
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dma_record_flush()
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let mut data = dma_record_output_prepare(timestamp, channel, address, 1);
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for word in words.as_ref().iter() {
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data[..4].copy_from_slice(&[
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(word >> 0) as u8,
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(word >> 8) as u8,
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(word >> 16) as u8,
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(word >> 24) as u8,
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]);
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data = &mut data[4..];
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}
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let dst = &mut DMA_RECORDER.buffer[DMA_RECORDER.data_len..
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DMA_RECORDER.data_len + length];
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dst[..header_length].copy_from_slice(&header[..]);
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dst[header_length..].copy_from_slice(&data[..]);
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DMA_RECORDER.data_len += length;
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}
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}
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@ -641,7 +641,7 @@ class DMATest(ExperimentCase):
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exp.record_many(count)
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dt = self.dataset_mgr.get("dma_record_time")
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print("dt={}, dt/count={}".format(dt, dt/count))
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self.assertLess(dt/count, 20*us)
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self.assertLess(dt/count, 11*us)
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def test_dma_playback_time(self):
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# Skip on Kasli until #946 is resolved.
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