hardfault fixed

.gitignore

@@ -1 +1,2 @@
 *.pdf
+dma_example/

dma_gpio2/src/bin/main.rs

@@ -1,102 +1,95 @@
 // src/bin/main.rs
+
 #![no_std]
 #![no_main]
 
 use defmt::*;
 use embassy_executor::Spawner;
 use embassy_futures::yield_now;
-use embassy_stm32::dma::Request;
 use embassy_stm32::gpio::{Input, Output, Level, Pull, Speed};
-use embassy_sync::{blocking_mutex::raw::CriticalSectionRawMutex, pipe::Pipe};
-use embassy_time::{Duration, Timer};
-use embassy_stm32::dma::{TransferOptions, WritableRingBuffer};
+use embassy_stm32::dma::{TransferOptions, Transfer, Priority, Request};
 use dma_gpio::software_uart::{
     dma_timer::init_tim6_for_uart,
     gpio_dma_uart_tx::encode_uart_frames,
     debug::dump_tim6_regs,
 };
-use dma_gpio::config::{BAUD, TX_PIN_BIT, RX_OVERSAMPLE, TX_OVERSAMPLE};
-use dma_gpio::config::{TX_RING_BYTES, RX_RING_BYTES, PIPE_RX_SIZE};
+use dma_gpio::config::{BAUD, TX_PIN_BIT, TX_OVERSAMPLE};
 use static_cell::StaticCell;
 use {defmt_rtt as _, panic_probe as _};
 
-// kapitola 17.4.11 - 2 casovace pre 2 DMA
-pub const TIM6_UP_REQ: Request = 4; // Table 137: tim6_upd_dma, strana 687 STM32U5xx datasheet
-
-static TX_RING: StaticCell<[u32; TX_RING_BYTES]> = StaticCell::new();
-
-use core::future::poll_fn;
-use core::task::Poll;
-
-async fn wait_for_space<'a, W: embassy_stm32::dma::word::Word>(
-    ring: &mut embassy_stm32::dma::WritableRingBuffer<'a, W>,
-    min_free: usize,
-) {
-    poll_fn(|cx| {
-        let used = ring.len().unwrap_or(0);
-        let cap = ring.capacity();
-        if cap - used > min_free {
-            Poll::Ready(())
-        } else {
-            ring.set_waker(cx.waker());
-            Poll::Pending
-        }
-    }).await
+unsafe fn start_dma<'a>(
+    ch: embassy_hal_internal::Peri<'a, impl embassy_stm32::dma::Channel>,
+    request: Request,
+    odr_ptr: *mut u32,
+    buf: &'a [u32],
+    opts: TransferOptions,
+) -> Transfer<'a> {
+    // new_write itself is unsafe
+    unsafe { Transfer::new_write(ch, request, buf, odr_ptr, opts) }
 }
 
-#[embassy_executor::main]
-async fn main(spawner: Spawner) {
-    let p = embassy_stm32::init(Default::default());
-    info!("Hehe");
+pub const TIM6_UP_REQ: Request = 4;
+const DMA_BUF_WORDS: usize = 256;
 
-    let _rx = Input::new(p.PA3, Pull::Up);
-    let _tx = Output::new(p.PA2, Level::High, Speed::VeryHigh);
+static BUF_A: StaticCell<[u32; DMA_BUF_WORDS]> = StaticCell::new();
+static BUF_B: StaticCell<[u32; DMA_BUF_WORDS]> = StaticCell::new();
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_stm32::init(Default::default());
+    let odr_ptr = embassy_stm32::pac::GPIOA.odr().as_ptr() as *mut u32;
 
     init_tim6_for_uart(p.TIM6, BAUD, TX_OVERSAMPLE);
     dump_tim6_regs();
 
-    // Safe one-time init from StaticCell
-    let tx_ring_mem: &mut [u32; TX_RING_BYTES] = TX_RING.init([0; TX_RING_BYTES]);
+    let buf_a = BUF_A.init([0u32; DMA_BUF_WORDS]);
+    let buf_b = BUF_B.init([0u32; DMA_BUF_WORDS]);
+    // Pre-fill with idle high level (stop bit level)
+    let idle = 1u32 << TX_PIN_BIT;
+    for w in buf_a.iter_mut() {
+        *w = idle;
+    }
+    for w in buf_b.iter_mut() {
+        *w = idle;
+    }
 
-    // Create and start the TX DMA ring in main.
-    // let bsrr_ptr = embassy_stm32::pac::GPIOA.bsrr().as_ptr() as *mut u32;
-    let odr_ptr = embassy_stm32::pac::GPIOA.odr().as_ptr() as *mut u32;
-    let mut tx_opts = TransferOptions::default();
-    tx_opts.half_transfer_ir = true;
-    tx_opts.complete_transfer_ir = true;
+    let mut opts = TransferOptions::default();
+    opts.priority = Priority::VeryHigh;
+    opts.complete_transfer_ir = true;
 
-    // SAFETY: tx_ring_mem is exclusive
-    let mut tx_ring = unsafe {
-        WritableRingBuffer::new(
-            p.GPDMA1_CH0,
-            TIM6_UP_REQ,
-            odr_ptr,
-            tx_ring_mem,
-            tx_opts,
-        )
-    };
-    // Start DMA
-    tx_ring.start();
-    info!("TX DMA ring started");
-
-    let mut frame_buf = [0u32; 4096];
+    let mut ch0 = p.GPDMA1_CH0;
+    let mut using_a = true;
 
     loop {
-        info!("tick start");
-        Timer::after(Duration::from_millis(400)).await;
-        info!("tick end");
-
-        let used = encode_uart_frames(TX_PIN_BIT, b"Hello marshmallow\r\n", &mut frame_buf).await;
-
-        // Wait for DMA to free space, async style
-        wait_for_space(&mut tx_ring, used / 2).await;
-
-        if let Err(e) = tx_ring.write_exact(&frame_buf[..used]).await {
-            warn!("DMA ring write error: {:?}", e);
+        let (dma_buf, cpu_buf) = if using_a {
+            (&*buf_a, &mut *buf_b)
         } else {
-            info!("Frame queued to DMA ring");
+            (&*buf_b, &mut *buf_a)
+        };
+
+        // Start from idle pattern
+        let idle = 1u32 << TX_PIN_BIT;
+        for w in cpu_buf.iter_mut() {
+            *w = idle;
         }
 
+        let used = encode_uart_frames(TX_PIN_BIT, b"Hello marshmallow\r\n", cpu_buf).await;
+
+        let len = if used == 0 { 1 } else { used };
+        // At least one word so DMA is always valid.
+
+        let transfer = unsafe {
+            start_dma(
+                ch0.reborrow(),
+                TIM6_UP_REQ,
+                odr_ptr,
+                &dma_buf[..len],
+                opts,
+            )
+        };
+        transfer.await;
+        using_a = !using_a;
+
         yield_now().await;
     }
 }