Merge #500

500: Low level DMA channel API. r=Dirbaio a=matoushybl

This should be an improved version of the PR by `@theunkn0wn1.`

Co-authored-by: Joshua Salzedo <[email protected]>
Co-authored-by: Matous Hybl <[email protected]>
Co-authored-by: Dario Nieuwenhuis <[email protected]>

9 files changed, 593 insertions, 403 deletions

diff --git a/embassy-stm32/src/dma/bdma.rs b/embassy-stm32/src/dma/bdma.rs
index 35c0b3ee7..b4c77757e 100644
--- a/embassy-stm32/src/dma/bdma.rs
+++ b/embassy-stm32/src/dma/bdma.rs
@@ -1,20 +1,29 @@
 #![macro_use]
 
-use core::future::Future;
 use core::sync::atomic::{fence, Ordering};
-use core::task::Poll;
+use core::task::Waker;
 
 use embassy::interrupt::{Interrupt, InterruptExt};
 use embassy::waitqueue::AtomicWaker;
-use embassy_hal_common::drop::OnDrop;
-use futures::future::poll_fn;
 
-use crate::dma::{Channel, Request};
+use crate::dma::Request;
 use crate::interrupt;
 use crate::pac;
 use crate::pac::bdma::vals;
 use crate::rcc::sealed::RccPeripheral;
 
+use super::{Word, WordSize};
+
+impl From<WordSize> for vals::Size {
+    fn from(raw: WordSize) -> Self {
+        match raw {
+            WordSize::OneByte => Self::BITS8,
+            WordSize::TwoBytes => Self::BITS16,
+            WordSize::FourBytes => Self::BITS32,
+        }
+    }
+}
+
 const CH_COUNT: usize = pac::peripheral_count!(bdma) * 8;
 
 struct State {
@@ -32,92 +41,6 @@ impl State {
 
 static STATE: State = State::new();
 
-#[allow(unused)]
-pub(crate) unsafe fn do_transfer(
-    dma: pac::bdma::Dma,
-    channel_number: u8,
-    state_number: u8,
-    request: Request,
-    dir: vals::Dir,
-    peri_addr: *const u8,
-    mem_addr: *mut u8,
-    mem_len: usize,
-    incr_mem: bool,
-    #[cfg(dmamux)] dmamux_regs: pac::dmamux::Dmamux,
-    #[cfg(dmamux)] dmamux_ch_num: u8,
-) -> impl Future<Output = ()> {
-    // ndtr is max 16 bits.
-    assert!(mem_len <= 0xFFFF);
-
-    let ch = dma.ch(channel_number as _);
-
-    // Reset status
-    dma.ifcr().write(|w| {
-        w.set_tcif(channel_number as _, true);
-        w.set_teif(channel_number as _, true);
-    });
-
-    let on_drop = OnDrop::new(move || unsafe {
-        // Disable the channel and interrupts with the default value.
-        ch.cr().write(|_| ());
-
-        // Wait for the transfer to complete when it was ongoing.
-        while ch.cr().read().en() {}
-
-        // "Subsequent reads and writes cannot be moved ahead of preceding reads."
-        fence(Ordering::Acquire);
-    });
-
-    #[cfg(dmamux)]
-    super::dmamux::configure_dmamux(dmamux_regs, dmamux_ch_num, request);
-
-    #[cfg(bdma_v2)]
-    critical_section::with(|_| {
-        dma.cselr()
-            .modify(|w| w.set_cs(channel_number as _, request))
-    });
-
-    // "Preceding reads and writes cannot be moved past subsequent writes."
-    fence(Ordering::Release);
-
-    ch.par().write_value(peri_addr as u32);
-    ch.mar().write_value(mem_addr as u32);
-    ch.ndtr().write(|w| w.set_ndt(mem_len as u16));
-    ch.cr().write(|w| {
-        w.set_psize(vals::Size::BITS8);
-        w.set_msize(vals::Size::BITS8);
-        if incr_mem {
-            w.set_minc(vals::Inc::ENABLED);
-        } else {
-            w.set_minc(vals::Inc::DISABLED);
-        }
-        w.set_dir(dir);
-        w.set_teie(true);
-        w.set_tcie(true);
-        w.set_en(true);
-    });
-
-    async move {
-        let res = poll_fn(|cx| {
-            STATE.ch_wakers[state_number as usize].register(cx.waker());
-
-            let isr = dma.isr().read();
-
-            // TODO handle error
-            assert!(!isr.teif(channel_number as _));
-
-            if isr.tcif(channel_number as _) {
-                Poll::Ready(())
-            } else {
-                Poll::Pending
-            }
-        })
-        .await;
-
-        drop(on_drop)
-    }
-}
-
 macro_rules! dma_num {
     (DMA1) => {
         0
@@ -136,7 +59,7 @@ unsafe fn on_irq() {
                 let isr = pac::$dma.isr().read();
                 let dman = dma_num!($dma);
 
-                for chn in 0..crate::pac::dma_channels_count!($dma) {
+                for chn in 0..pac::dma_channels_count!($dma) {
                     let cr = pac::$dma.ch(chn).cr();
                     if isr.tcif(chn) && cr.read().tcie() {
                         cr.write(|_| ()); // Disable channel interrupts with the default value.
@@ -164,88 +87,84 @@ pub(crate) unsafe fn init() {
 
 pac::dma_channels! {
     ($channel_peri:ident, $dma_peri:ident, bdma, $channel_num:expr, $dmamux:tt) => {
-        impl crate::dma::sealed::Channel for crate::peripherals::$channel_peri {}
-        impl Channel for crate::peripherals::$channel_peri
-        {
-            type ReadFuture<'a> = impl Future<Output = ()> + 'a;
-            type WriteFuture<'a> = impl Future<Output = ()> + 'a;
-
-            fn read<'a>(
-                &'a mut self,
-                request: Request,
-                src: *mut u8,
-                buf: &'a mut [u8],
-            ) -> Self::ReadFuture<'a> {
-                unsafe {
-                    do_transfer(
-                        crate::pac::$dma_peri,
-                        $channel_num,
-                        (dma_num!($dma_peri) * 8) + $channel_num,
-                        request,
-                        vals::Dir::FROMPERIPHERAL,
-                        src,
-                        buf.as_mut_ptr(),
-                        buf.len(),
-                        true,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
-                    )
-                }
+        impl crate::dma::sealed::Channel for crate::peripherals::$channel_peri {
+
+            unsafe fn start_write<W: Word>(&mut self, request: Request, buf: &[W], reg_addr: *mut W) {
+                low_level_api::start_transfer(
+                    pac::$dma_peri,
+                    $channel_num,
+                    #[cfg(any(bdma_v2, dmamux))]
+                    request,
+                    vals::Dir::FROMMEMORY,
+                    reg_addr as *const u32,
+                    buf.as_ptr() as *mut u32,
+                    buf.len(),
+                    true,
+                    vals::Size::from(W::bits()),
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
+                );
             }
 
-            fn write<'a>(
-                &'a mut self,
-                request: Request,
-                buf: &'a [u8],
-                dst: *mut u8,
-            ) -> Self::WriteFuture<'a> {
-                unsafe {
-                    do_transfer(
-                        crate::pac::$dma_peri,
-                        $channel_num,
-                        (dma_num!($dma_peri) * 8) + $channel_num,
-                        request,
-                        vals::Dir::FROMMEMORY,
-                        dst,
-                        buf.as_ptr() as *mut u8,
-                        buf.len(),
-                        true,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
-                    )
-                }
+
+            unsafe fn start_write_repeated<W: Word>(&mut self, request: Request, repeated: W, count: usize, reg_addr: *mut W) {
+                let buf = [repeated];
+                low_level_api::start_transfer(
+                    pac::$dma_peri,
+                    $channel_num,
+                    #[cfg(any(bdma_v2, dmamux))]
+                    request,
+                    vals::Dir::FROMMEMORY,
+                    reg_addr as *const u32,
+                    buf.as_ptr() as *mut u32,
+                    count,
+                    false,
+                    vals::Size::from(W::bits()),
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
+                )
             }
 
-            fn write_x<'a>(
-                &'a mut self,
-                request: Request,
-                word: &u8,
-                count: usize,
-                dst: *mut u8,
-            ) -> Self::WriteFuture<'a> {
-                unsafe {
-                    do_transfer(
-                        crate::pac::$dma_peri,
-                        $channel_num,
-                        (dma_num!($dma_peri) * 8) + $channel_num,
-                        request,
-                        vals::Dir::FROMMEMORY,
-                        dst,
-                        word as *const u8 as *mut u8,
-                        count,
-                        false,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
-                    )
-                }
+            unsafe fn start_read<W: Word>(&mut self, request: Request, reg_addr: *mut W, buf: &mut [W]) {
+                low_level_api::start_transfer(
+                    pac::$dma_peri,
+                    $channel_num,
+                    #[cfg(any(bdma_v2, dmamux))]
+                    request,
+                    vals::Dir::FROMPERIPHERAL,
+                    reg_addr as *const u32,
+                    buf.as_ptr() as *mut u32,
+                    buf.len(),
+                    true,
+                    vals::Size::from(W::bits()),
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
+                );
+            }
+
+            fn request_stop(&mut self){
+                unsafe {low_level_api::request_stop(pac::$dma_peri, $channel_num);}
+            }
+
+            fn is_running(&self) -> bool {
+                unsafe {low_level_api::is_running(pac::$dma_peri, $channel_num)}
+            }
+            fn remaining_transfers(&mut self) -> u16 {
+                unsafe {low_level_api::get_remaining_transfers(pac::$dma_peri, $channel_num)}
+            }
+
+            fn set_waker(&mut self, waker: &Waker) {
+                unsafe {low_level_api::set_waker(dma_num!($dma_peri) * 8 + $channel_num, waker )}
             }
         }
+
+        impl crate::dma::Channel for crate::peripherals::$channel_peri {}
     };
 }
 
@@ -257,3 +176,92 @@ pac::interrupts! {
         }
     };
 }
+
+mod low_level_api {
+    use super::*;
+
+    pub unsafe fn start_transfer(
+        dma: pac::bdma::Dma,
+        channel_number: u8,
+        #[cfg(any(bdma_v2, dmamux))] request: Request,
+        dir: vals::Dir,
+        peri_addr: *const u32,
+        mem_addr: *mut u32,
+        mem_len: usize,
+        incr_mem: bool,
+        data_size: vals::Size,
+        #[cfg(dmamux)] dmamux_regs: pac::dmamux::Dmamux,
+        #[cfg(dmamux)] dmamux_ch_num: u8,
+    ) {
+        let ch = dma.ch(channel_number as _);
+
+        reset_status(dma, channel_number);
+
+        #[cfg(dmamux)]
+        super::super::dmamux::configure_dmamux(dmamux_regs, dmamux_ch_num, request);
+
+        #[cfg(bdma_v2)]
+        critical_section::with(|_| {
+            dma.cselr()
+                .modify(|w| w.set_cs(channel_number as _, request))
+        });
+
+        // "Preceding reads and writes cannot be moved past subsequent writes."
+        fence(Ordering::SeqCst);
+
+        ch.par().write_value(peri_addr as u32);
+        ch.mar().write_value(mem_addr as u32);
+        ch.ndtr().write(|w| w.set_ndt(mem_len as u16));
+        ch.cr().write(|w| {
+            w.set_psize(data_size);
+            w.set_msize(data_size);
+            if incr_mem {
+                w.set_minc(vals::Inc::ENABLED);
+            } else {
+                w.set_minc(vals::Inc::DISABLED);
+            }
+            w.set_dir(dir);
+            w.set_teie(true);
+            w.set_tcie(true);
+            w.set_en(true);
+        });
+    }
+
+    pub unsafe fn request_stop(dma: pac::bdma::Dma, channel_number: u8) {
+        reset_status(dma, channel_number);
+
+        let ch = dma.ch(channel_number as _);
+
+        // Disable the channel and interrupts with the default value.
+        ch.cr().write(|_| ());
+
+        // "Subsequent reads and writes cannot be moved ahead of preceding reads."
+        fence(Ordering::SeqCst);
+    }
+
+    pub unsafe fn is_running(dma: pac::bdma::Dma, ch: u8) -> bool {
+        let ch = dma.ch(ch as _);
+        ch.cr().read().en()
+    }
+
+    /// Gets the total remaining transfers for the channel
+    /// Note: this will be zero for transfers that completed without cancellation.
+    pub unsafe fn get_remaining_transfers(dma: pac::bdma::Dma, ch: u8) -> u16 {
+        // get a handle on the channel itself
+        let ch = dma.ch(ch as _);
+        // read the remaining transfer count. If this is zero, the transfer completed fully.
+        ch.ndtr().read().ndt()
+    }
+
+    /// Sets the waker for the specified DMA channel
+    pub unsafe fn set_waker(state_number: usize, waker: &Waker) {
+        STATE.ch_wakers[state_number].register(waker);
+    }
+
+    pub unsafe fn reset_status(dma: pac::bdma::Dma, channel_number: u8) {
+        dma.ifcr().write(|w| {
+            w.set_tcif(channel_number as _, true);
+            w.set_teif(channel_number as _, true);
+        });
+    }
+}
diff --git a/embassy-stm32/src/dma/dma.rs b/embassy-stm32/src/dma/dma.rs
index ec5ac98a0..efe4d1d9d 100644
--- a/embassy-stm32/src/dma/dma.rs
+++ b/embassy-stm32/src/dma/dma.rs
@@ -1,21 +1,28 @@
-use core::future::Future;
 use core::sync::atomic::{fence, Ordering};
-use core::task::Poll;
+use core::task::Waker;
 
 use embassy::interrupt::{Interrupt, InterruptExt};
 use embassy::waitqueue::AtomicWaker;
-use embassy_hal_common::drop::OnDrop;
-use futures::future::poll_fn;
 
 use crate::interrupt;
 use crate::pac;
 use crate::pac::dma::{regs, vals};
 use crate::rcc::sealed::RccPeripheral;
 
-use super::{Channel, Request};
+use super::{Request, Word, WordSize};
 
 const CH_COUNT: usize = pac::peripheral_count!(DMA) * 8;
 
+impl From<WordSize> for vals::Size {
+    fn from(raw: WordSize) -> Self {
+        match raw {
+            WordSize::OneByte => Self::BITS8,
+            WordSize::TwoBytes => Self::BITS16,
+            WordSize::FourBytes => Self::BITS32,
+        }
+    }
+}
+
 struct State {
     ch_wakers: [AtomicWaker; CH_COUNT],
 }
@@ -31,100 +38,6 @@ impl State {
 
 static STATE: State = State::new();
 
-//async unsafe fn do_transfer(ch: &mut impl Channel, ch_func: u8, src: *const u8, dst: &mut [u8]) {
-
-#[allow(unused)]
-pub(crate) unsafe fn do_transfer(
-    dma: pac::dma::Dma,
-    channel_number: u8,
-    state_number: u8,
-    request: Request,
-    dir: vals::Dir,
-    peri_addr: *const u8,
-    mem_addr: *mut u8,
-    mem_len: usize,
-    incr_mem: bool,
-    #[cfg(dmamux)] dmamux_regs: pac::dmamux::Dmamux,
-    #[cfg(dmamux)] dmamux_ch_num: u8,
-) -> impl Future<Output = ()> {
-    // ndtr is max 16 bits.
-    assert!(mem_len <= 0xFFFF);
-
-    // Reset status
-    let isrn = channel_number as usize / 4;
-    let isrbit = channel_number as usize % 4;
-    dma.ifcr(isrn).write(|w| {
-        w.set_tcif(isrbit, true);
-        w.set_teif(isrbit, true);
-    });
-
-    let ch = dma.st(channel_number as _);
-
-    let on_drop = OnDrop::new(move || unsafe {
-        // Disable the channel and interrupts with the default value.
-        ch.cr().write(|_| ());
-
-        // Wait for the transfer to complete when it was ongoing.
-        while ch.cr().read().en() {}
-
-        // "Subsequent reads and writes cannot be moved ahead of preceding reads."
-        fence(Ordering::Acquire);
-    });
-
-    #[cfg(dmamux)]
-    super::dmamux::configure_dmamux(dmamux_regs, dmamux_ch_num, request);
-
-    // "Preceding reads and writes cannot be moved past subsequent writes."
-    fence(Ordering::Release);
-
-    unsafe {
-        ch.par().write_value(peri_addr as u32);
-        ch.m0ar().write_value(mem_addr as u32);
-        ch.ndtr().write_value(regs::Ndtr(mem_len as _));
-        ch.cr().write(|w| {
-            w.set_dir(dir);
-            w.set_msize(vals::Size::BITS8);
-            w.set_psize(vals::Size::BITS8);
-            if incr_mem {
-                w.set_minc(vals::Inc::INCREMENTED);
-            } else {
-                w.set_minc(vals::Inc::FIXED);
-            }
-            w.set_pinc(vals::Inc::FIXED);
-            w.set_teie(true);
-            w.set_tcie(true);
-            #[cfg(dma_v1)]
-            w.set_trbuff(true);
-
-            #[cfg(dma_v2)]
-            w.set_chsel(request);
-
-            w.set_en(true);
-        });
-    }
-
-    async move {
-        let res = poll_fn(|cx| {
-            let n = state_number as usize;
-            STATE.ch_wakers[n].register(cx.waker());
-
-            let isr = dma.isr(isrn).read();
-
-            // TODO handle error
-            assert!(!isr.teif(isrbit));
-
-            if isr.tcif(isrbit) {
-                Poll::Ready(())
-            } else {
-                Poll::Pending
-            }
-        })
-        .await;
-
-        drop(on_drop)
-    }
-}
-
 macro_rules! dma_num {
     (DMA1) => {
         0
@@ -170,88 +83,80 @@ pub(crate) unsafe fn init() {
 
 pac::dma_channels! {
     ($channel_peri:ident, $dma_peri:ident, dma, $channel_num:expr, $dmamux:tt) => {
-        impl crate::dma::sealed::Channel for crate::peripherals::$channel_peri {}
-        impl Channel for crate::peripherals::$channel_peri
-        {
-            type ReadFuture<'a> = impl Future<Output = ()> + 'a;
-            type WriteFuture<'a> = impl Future<Output = ()> + 'a;
-
-            fn read<'a>(
-                &'a mut self,
-                request: Request,
-                src: *mut u8,
-                buf: &'a mut [u8],
-            ) -> Self::ReadFuture<'a> {
-                unsafe {
-                    do_transfer(
-                        crate::pac::$dma_peri,
-                        $channel_num,
-                        (dma_num!($dma_peri) * 8) + $channel_num,
-                        request,
-                        vals::Dir::PERIPHERALTOMEMORY,
-                        src,
-                        buf.as_mut_ptr(),
-                        buf.len(),
-                        true,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
-                    )
-                }
+        impl crate::dma::sealed::Channel for crate::peripherals::$channel_peri {
+            unsafe fn start_write<W: Word>(&mut self, request: Request, buf: &[W], reg_addr: *mut W) {
+                low_level_api::start_transfer(
+                    pac::$dma_peri,
+                    $channel_num,
+                    request,
+                    vals::Dir::MEMORYTOPERIPHERAL,
+                    reg_addr as *const u32,
+                    buf.as_ptr() as *mut u32,
+                    buf.len(),
+                    true,
+                    vals::Size::from(W::bits()),
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
+                )
             }
 
-            fn write<'a>(
-                &'a mut self,
-                request: Request,
-                buf: &'a [u8],
-                dst: *mut u8,
-            ) -> Self::WriteFuture<'a> {
-                unsafe {
-                    do_transfer(
-                        crate::pac::$dma_peri,
-                        $channel_num,
-                        (dma_num!($dma_peri) * 8) + $channel_num,
-                        request,
-                        vals::Dir::MEMORYTOPERIPHERAL,
-                        dst,
-                        buf.as_ptr() as *mut u8,
-                        buf.len(),
-                        true,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
-                    )
-                }
+            unsafe fn start_write_repeated<W: Word>(&mut self, request: Request, repeated: W, count: usize, reg_addr: *mut W) {
+                let buf = [repeated];
+                low_level_api::start_transfer(
+                    pac::$dma_peri,
+                    $channel_num,
+                    request,
+                    vals::Dir::MEMORYTOPERIPHERAL,
+                    reg_addr as *const u32,
+                    buf.as_ptr() as *mut u32,
+                    count,
+                    false,
+                    vals::Size::from(W::bits()),
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
+                )
             }
 
-            fn write_x<'a>(
-                &'a mut self,
-                request: Request,
-                word: &u8,
-                num: usize,
-                dst: *mut u8,
-            ) -> Self::WriteFuture<'a> {
-                unsafe {
-                    do_transfer(
-                        crate::pac::$dma_peri,
-                        $channel_num,
-                        (dma_num!($dma_peri) * 8) + $channel_num,
-                        request,
-                        vals::Dir::MEMORYTOPERIPHERAL,
-                        dst,
-                        word as *const u8 as *mut u8,
-                        num,
-                        false,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
-                        #[cfg(dmamux)]
-                        <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
-                    )
-                }
+            unsafe fn start_read<W: Word>(&mut self, request: Request, reg_addr: *mut W, buf: &mut [W]) {
+                low_level_api::start_transfer(
+                    pac::$dma_peri,
+                    $channel_num,
+                    request,
+                    vals::Dir::PERIPHERALTOMEMORY,
+                    reg_addr as *const u32,
+                    buf.as_ptr() as *mut u32,
+                    buf.len(),
+                    true,
+                    vals::Size::from(W::bits()),
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_REGS,
+                    #[cfg(dmamux)]
+                    <Self as super::dmamux::sealed::MuxChannel>::DMAMUX_CH_NUM,
+                );
+            }
+
+            fn request_stop(&mut self) {
+                unsafe {low_level_api::request_stop(pac::$dma_peri, $channel_num);}
+            }
+
+            fn is_running(&self) -> bool {
+                unsafe {low_level_api::is_running(pac::$dma_peri, $channel_num)}
+            }
+
+            fn remaining_transfers(&mut self) -> u16 {
+                unsafe {low_level_api::get_remaining_transfers(pac::$dma_peri, $channel_num)}
+            }
+
+            fn set_waker(&mut self, waker: &Waker) {
+                unsafe {low_level_api::set_waker(dma_num!($dma_peri) * 8 + $channel_num, waker )}
             }
         }
+
+        impl crate::dma::Channel for crate::peripherals::$channel_peri { }
     };
 }
 
@@ -263,3 +168,102 @@ pac::interrupts! {
         }
     };
 }
+
+mod low_level_api {
+    use super::*;
+
+    pub unsafe fn start_transfer(
+        dma: pac::dma::Dma,
+        channel_number: u8,
+        request: Request,
+        dir: vals::Dir,
+        peri_addr: *const u32,
+        mem_addr: *mut u32,
+        mem_len: usize,
+        incr_mem: bool,
+        data_size: vals::Size,
+        #[cfg(dmamux)] dmamux_regs: pac::dmamux::Dmamux,
+        #[cfg(dmamux)] dmamux_ch_num: u8,
+    ) {
+        #[cfg(dmamux)]
+        super::super::dmamux::configure_dmamux(dmamux_regs, dmamux_ch_num, request);
+
+        // "Preceding reads and writes cannot be moved past subsequent writes."
+        fence(Ordering::SeqCst);
+
+        reset_status(dma, channel_number);
+
+        let ch = dma.st(channel_number as _);
+        ch.par().write_value(peri_addr as u32);
+        ch.m0ar().write_value(mem_addr as u32);
+        ch.ndtr().write_value(regs::Ndtr(mem_len as _));
+        ch.cr().write(|w| {
+            w.set_dir(dir);
+            w.set_msize(data_size);
+            w.set_psize(data_size);
+            w.set_pl(vals::Pl::VERYHIGH);
+            if incr_mem {
+                w.set_minc(vals::Inc::INCREMENTED);
+            } else {
+                w.set_minc(vals::Inc::FIXED);
+            }
+            w.set_pinc(vals::Inc::FIXED);
+            w.set_teie(true);
+            w.set_tcie(true);
+            #[cfg(dma_v1)]
+            w.set_trbuff(true);
+
+            #[cfg(dma_v2)]
+            w.set_chsel(request);
+
+            w.set_en(true);
+        });
+    }
+
+    /// Stops the DMA channel.
+    pub unsafe fn request_stop(dma: pac::dma::Dma, channel_number: u8) {
+        // get a handle on the channel itself
+        let ch = dma.st(channel_number as _);
+
+        // Disable the channel. Keep the IEs enabled so the irqs still fire.
+        ch.cr().write(|w| {
+            w.set_teie(true);
+            w.set_tcie(true);
+        });
+
+        // "Subsequent reads and writes cannot be moved ahead of preceding reads."
+        fence(Ordering::SeqCst);
+    }
+
+    /// Gets the running status of the channel
+    pub unsafe fn is_running(dma: pac::dma::Dma, ch: u8) -> bool {
+        // get a handle on the channel itself
+        let ch = dma.st(ch as _);
+        // Get whether it's enabled (running)
+        ch.cr().read().en()
+    }
+
+    /// Gets the total remaining transfers for the channel
+    /// Note: this will be zero for transfers that completed without cancellation.
+    pub unsafe fn get_remaining_transfers(dma: pac::dma::Dma, ch: u8) -> u16 {
+        // get a handle on the channel itself
+        let ch = dma.st(ch as _);
+        // read the remaining transfer count. If this is zero, the transfer completed fully.
+        ch.ndtr().read().ndt()
+    }
+
+    /// Sets the waker for the specified DMA channel
+    pub unsafe fn set_waker(state_number: usize, waker: &Waker) {
+        STATE.ch_wakers[state_number].register(waker);
+    }
+
+    pub unsafe fn reset_status(dma: pac::dma::Dma, channel_number: u8) {
+        let isrn = channel_number as usize / 4;
+        let isrbit = channel_number as usize % 4;
+
+        dma.ifcr(isrn).write(|w| {
+            w.set_tcif(isrbit, true);
+            w.set_teif(isrbit, true);
+        });
+    }
+}
diff --git a/embassy-stm32/src/dma/mod.rs b/embassy-stm32/src/dma/mod.rs
index 60f6a3020..accc55653 100644
--- a/embassy-stm32/src/dma/mod.rs
+++ b/embassy-stm32/src/dma/mod.rs
@@ -9,7 +9,18 @@ mod dmamux;
 pub use dmamux::*;
 
 use core::future::Future;
+use core::marker::PhantomData;
+use core::pin::Pin;
+use core::task::Waker;
+use core::task::{Context, Poll};
 use embassy::util::Unborrow;
+use embassy_hal_common::unborrow;
+
+#[cfg(feature = "unstable-pac")]
+pub use transfers::*;
+
+#[cfg(not(feature = "unstable-pac"))]
+pub(crate) use transfers::*;
 
 #[cfg(any(bdma_v2, dma_v2, dmamux))]
 pub type Request = u8;
@@ -17,41 +28,180 @@ pub type Request = u8;
 pub type Request = ();
 
 pub(crate) mod sealed {
-    pub trait Channel {}
+    use super::*;
+
+    pub trait Word {}
+
+    pub trait Channel {
+        /// Starts this channel for writing a stream of words.
+        ///
+        /// Safety:
+        /// - `buf` must be alive for the entire duration of the DMA transfer.
+        /// - `reg_addr` must be a valid peripheral register address to write to.
+        unsafe fn start_write<W: super::Word>(
+            &mut self,
+            request: Request,
+            buf: &[W],
+            reg_addr: *mut W,
+        );
+
+        /// Starts this channel for writing a word repeatedly.
+        ///
+        /// Safety:
+        /// - `reg_addr` must be a valid peripheral register address to write to.
+        unsafe fn start_write_repeated<W: super::Word>(
+            &mut self,
+            request: Request,
+            repeated: W,
+            count: usize,
+            reg_addr: *mut W,
+        );
+
+        /// Starts this channel for reading a stream of words.
+        ///
+        /// Safety:
+        /// - `buf` must be alive for the entire duration of the DMA transfer.
+        /// - `reg_addr` must be a valid peripheral register address to write to.
+        unsafe fn start_read<W: super::Word>(
+            &mut self,
+            request: Request,
+            reg_addr: *mut W,
+            buf: &mut [W],
+        );
+
+        /// Requests the channel to stop.
+        /// NOTE: The channel does not immediately stop, you have to wait
+        /// for `is_running() = false`.
+        fn request_stop(&mut self);
+
+        /// Returns whether this channel is running or stopped.
+        ///
+        /// The channel stops running when it either completes or is manually stopped.
+        fn is_running(&self) -> bool;
+
+        /// Returns the total number of remaining transfers.
+        fn remaining_transfers(&mut self) -> u16;
+
+        /// Sets the waker that is called when this channel stops (either completed or manually stopped)
+        fn set_waker(&mut self, waker: &Waker);
+    }
+}
+
+pub enum WordSize {
+    OneByte,
+    TwoBytes,
+    FourBytes,
+}
+pub trait Word: sealed::Word {
+    fn bits() -> WordSize;
+}
+
+impl sealed::Word for u8 {}
+impl Word for u8 {
+    fn bits() -> WordSize {
+        WordSize::OneByte
+    }
+}
+
+impl sealed::Word for u16 {}
+impl Word for u16 {
+    fn bits() -> WordSize {
+        WordSize::TwoBytes
+    }
 }
 
-pub trait Channel: sealed::Channel {
-    type ReadFuture<'a>: Future<Output = ()> + 'a
-    where
-        Self: 'a;
+impl sealed::Word for u32 {}
+impl Word for u32 {
+    fn bits() -> WordSize {
+        WordSize::FourBytes
+    }
+}
 
-    type WriteFuture<'a>: Future<Output = ()> + 'a
-    where
-        Self: 'a;
+mod transfers {
+    use super::*;
 
-    fn read<'a>(
-        &'a mut self,
+    #[allow(unused)]
+    pub fn read<'a, W: Word>(
+        channel: impl Unborrow<Target = impl Channel> + 'a,
         request: Request,
-        src: *mut u8,
-        buf: &'a mut [u8],
-    ) -> Self::ReadFuture<'a>;
+        reg_addr: *mut W,
+        buf: &'a mut [W],
+    ) -> impl Future<Output = ()> + 'a {
+        assert!(buf.len() <= 0xFFFF);
+        unborrow!(channel);
+
+        unsafe { channel.start_read::<W>(request, reg_addr, buf) };
+
+        Transfer {
+            channel,
+            _phantom: PhantomData,
+        }
+    }
 
-    fn write<'a>(
-        &'a mut self,
+    #[allow(unused)]
+    pub fn write<'a, W: Word>(
+        channel: impl Unborrow<Target = impl Channel> + 'a,
         request: Request,
-        buf: &'a [u8],
-        dst: *mut u8,
-    ) -> Self::WriteFuture<'a>;
+        buf: &'a [W],
+        reg_addr: *mut W,
+    ) -> impl Future<Output = ()> + 'a {
+        assert!(buf.len() <= 0xFFFF);
+        unborrow!(channel);
+
+        unsafe { channel.start_write::<W>(request, buf, reg_addr) };
 
-    fn write_x<'a>(
-        &'a mut self,
+        Transfer {
+            channel,
+            _phantom: PhantomData,
+        }
+    }
+
+    #[allow(unused)]
+    pub fn write_repeated<'a, W: Word>(
+        channel: impl Unborrow<Target = impl Channel> + 'a,
         request: Request,
-        word: &u8,
-        num: usize,
-        dst: *mut u8,
-    ) -> Self::WriteFuture<'a>;
+        repeated: W,
+        count: usize,
+        reg_addr: *mut W,
+    ) -> impl Future<Output = ()> + 'a {
+        unborrow!(channel);
+
+        unsafe { channel.start_write_repeated::<W>(request, repeated, count, reg_addr) };
+
+        Transfer {
+            channel,
+            _phantom: PhantomData,
+        }
+    }
+
+    struct Transfer<'a, C: Channel> {
+        channel: C,
+        _phantom: PhantomData<&'a mut C>,
+    }
+
+    impl<'a, C: Channel> Drop for Transfer<'a, C> {
+        fn drop(&mut self) {
+            self.channel.request_stop();
+            while self.channel.is_running() {}
+        }
+    }
+
+    impl<'a, C: Channel> Unpin for Transfer<'a, C> {}
+    impl<'a, C: Channel> Future for Transfer<'a, C> {
+        type Output = ();
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            self.channel.set_waker(cx.waker());
+            if self.channel.is_running() {
+                Poll::Pending
+            } else {
+                Poll::Ready(())
+            }
+        }
+    }
 }
 
+pub trait Channel: sealed::Channel + Unborrow<Target = Self> + 'static {}
+
 pub struct NoDma;
 
 unsafe impl Unborrow for NoDma {
diff --git a/embassy-stm32/src/i2c/v2.rs b/embassy-stm32/src/i2c/v2.rs
index 11c8ab975..94c4d9a7c 100644
--- a/embassy-stm32/src/i2c/v2.rs
+++ b/embassy-stm32/src/i2c/v2.rs
@@ -418,7 +418,8 @@ impl<'d, T: Instance, TXDMA, RXDMA> I2c<'d, T, TXDMA, RXDMA> {
             let dst = regs.txdr().ptr() as *mut u8;
 
             let ch = &mut self.tx_dma;
-            ch.write(ch.request(), bytes, dst)
+            let request = ch.request();
+            crate::dma::write(ch, request, bytes, dst)
         };
 
         let state_number = T::state_number();
@@ -510,7 +511,8 @@ impl<'d, T: Instance, TXDMA, RXDMA> I2c<'d, T, TXDMA, RXDMA> {
             let src = regs.rxdr().ptr() as *mut u8;
 
             let ch = &mut self.rx_dma;
-            ch.read(ch.request(), src, buffer)
+            let request = ch.request();
+            crate::dma::read(ch, request, src, buffer)
         };
 
         let state_number = T::state_number();
diff --git a/embassy-stm32/src/spi/v1.rs b/embassy-stm32/src/spi/v1.rs
index 92449ea80..98f05770b 100644
--- a/embassy-stm32/src/spi/v1.rs
+++ b/embassy-stm32/src/spi/v1.rs
@@ -20,7 +20,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let request = self.txdma.request();
         let dst = T::regs().tx_ptr();
-        let f = self.txdma.write(request, write, dst);
+        let f = crate::dma::write(&mut self.txdma, request, write, dst);
 
         unsafe {
             T::regs().cr2().modify(|reg| {
@@ -54,14 +54,18 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let rx_request = self.rxdma.request();
         let rx_src = T::regs().rx_ptr();
-        let rx_f = self.rxdma.read(rx_request, rx_src, read);
+        let rx_f = crate::dma::read(&mut self.rxdma, rx_request, rx_src, read);
 
         let tx_request = self.txdma.request();
         let tx_dst = T::regs().tx_ptr();
-        let clock_byte = 0x00;
-        let tx_f = self
-            .txdma
-            .write_x(tx_request, &clock_byte, clock_byte_count, tx_dst);
+        let clock_byte = 0x00u8;
+        let tx_f = crate::dma::write_repeated(
+            &mut self.txdma,
+            tx_request,
+            clock_byte,
+            clock_byte_count,
+            tx_dst,
+        );
 
         unsafe {
             T::regs().cr2().modify(|reg| {
@@ -110,13 +114,16 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let rx_request = self.rxdma.request();
         let rx_src = T::regs().rx_ptr();
-        let rx_f = self
-            .rxdma
-            .read(rx_request, rx_src, &mut read[0..write.len()]);
+        let rx_f = crate::dma::read(
+            &mut self.rxdma,
+            rx_request,
+            rx_src,
+            &mut read[0..write.len()],
+        );
 
         let tx_request = self.txdma.request();
         let tx_dst = T::regs().tx_ptr();
-        let tx_f = self.txdma.write(tx_request, write, tx_dst);
+        let tx_f = crate::dma::write(&mut self.txdma, tx_request, write, tx_dst);
 
         unsafe {
             T::regs().cr2().modify(|reg| {
diff --git a/embassy-stm32/src/spi/v2.rs b/embassy-stm32/src/spi/v2.rs
index e24710dfe..286976329 100644
--- a/embassy-stm32/src/spi/v2.rs
+++ b/embassy-stm32/src/spi/v2.rs
@@ -24,7 +24,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let request = self.txdma.request();
         let dst = T::regs().tx_ptr();
-        let f = self.txdma.write(request, write, dst);
+        let f = crate::dma::write(&mut self.txdma, request, write, dst);
 
         unsafe {
             T::regs().cr2().modify(|reg| {
@@ -67,14 +67,18 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let rx_request = self.rxdma.request();
         let rx_src = T::regs().rx_ptr();
-        let rx_f = self.rxdma.read(rx_request, rx_src, read);
+        let rx_f = crate::dma::read(&mut self.rxdma, rx_request, rx_src, read);
 
         let tx_request = self.txdma.request();
         let tx_dst = T::regs().tx_ptr();
-        let clock_byte = 0x00;
-        let tx_f = self
-            .txdma
-            .write_x(tx_request, &clock_byte, clock_byte_count, tx_dst);
+        let clock_byte = 0x00u8;
+        let tx_f = crate::dma::write_repeated(
+            &mut self.txdma,
+            tx_request,
+            clock_byte,
+            clock_byte_count,
+            tx_dst,
+        );
 
         unsafe {
             T::regs().cr2().modify(|reg| {
@@ -128,13 +132,16 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let rx_request = self.rxdma.request();
         let rx_src = T::regs().rx_ptr();
-        let rx_f = self
-            .rxdma
-            .read(rx_request, rx_src, &mut read[0..write.len()]);
+        let rx_f = crate::dma::read(
+            &mut self.rxdma,
+            rx_request,
+            rx_src,
+            &mut read[0..write.len()],
+        );
 
         let tx_request = self.txdma.request();
         let tx_dst = T::regs().tx_ptr();
-        let tx_f = self.txdma.write(tx_request, write, tx_dst);
+        let tx_f = crate::dma::write(&mut self.txdma, tx_request, write, tx_dst);
 
         unsafe {
             T::regs().cr2().modify(|reg| {
diff --git a/embassy-stm32/src/spi/v3.rs b/embassy-stm32/src/spi/v3.rs
index 6d75de035..c31415a2f 100644
--- a/embassy-stm32/src/spi/v3.rs
+++ b/embassy-stm32/src/spi/v3.rs
@@ -24,7 +24,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let request = self.txdma.request();
         let dst = T::regs().tx_ptr();
-        let f = self.txdma.write(request, write, dst);
+        let f = crate::dma::write(&mut self.txdma, request, write, dst);
 
         unsafe {
             T::regs().cfg1().modify(|reg| {
@@ -70,14 +70,18 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let rx_request = self.rxdma.request();
         let rx_src = T::regs().rx_ptr();
-        let rx_f = self.rxdma.read(rx_request, rx_src, read);
+        let rx_f = crate::dma::read(&mut self.rxdma, rx_request, rx_src, read);
 
         let tx_request = self.txdma.request();
         let tx_dst = T::regs().tx_ptr();
-        let clock_byte = 0x00;
-        let tx_f = self
-            .txdma
-            .write_x(tx_request, &clock_byte, clock_byte_count, tx_dst);
+        let clock_byte = 0x00u8;
+        let tx_f = crate::dma::write_repeated(
+            &mut self.txdma,
+            tx_request,
+            clock_byte,
+            clock_byte_count,
+            tx_dst,
+        );
 
         unsafe {
             T::regs().cfg1().modify(|reg| {
@@ -132,13 +136,16 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
 
         let rx_request = self.rxdma.request();
         let rx_src = T::regs().rx_ptr();
-        let rx_f = self
-            .rxdma
-            .read(rx_request, rx_src, &mut read[0..write.len()]);
+        let rx_f = crate::dma::read(
+            &mut self.rxdma,
+            rx_request,
+            rx_src,
+            &mut read[0..write.len()],
+        );
 
         let tx_request = self.txdma.request();
         let tx_dst = T::regs().tx_ptr();
-        let tx_f = self.txdma.write(tx_request, write, tx_dst);
+        let tx_f = crate::dma::write(&mut self.txdma, tx_request, write, tx_dst);
 
         unsafe {
             T::regs().cfg1().modify(|reg| {
diff --git a/embassy-stm32/src/usart/v1.rs b/embassy-stm32/src/usart/v1.rs
index 8cd392d18..10f87f2dd 100644
--- a/embassy-stm32/src/usart/v1.rs
+++ b/embassy-stm32/src/usart/v1.rs
@@ -70,6 +70,7 @@ impl<'d, T: Instance, TxDma, RxDma> Uart<'d, T, TxDma, RxDma> {
         TxDma: crate::usart::TxDma<T>,
     {
         let ch = &mut self.tx_dma;
+        let request = ch.request();
         unsafe {
             self.inner.regs().cr3().modify(|reg| {
                 reg.set_dmat(true);
@@ -77,7 +78,7 @@ impl<'d, T: Instance, TxDma, RxDma> Uart<'d, T, TxDma, RxDma> {
         }
         let r = self.inner.regs();
         let dst = r.dr().ptr() as *mut u8;
-        ch.write(ch.request(), buffer, dst).await;
+        crate::dma::write(ch, request, buffer, dst).await;
         Ok(())
     }
 
@@ -86,6 +87,7 @@ impl<'d, T: Instance, TxDma, RxDma> Uart<'d, T, TxDma, RxDma> {
         RxDma: crate::usart::RxDma<T>,
     {
         let ch = &mut self.rx_dma;
+        let request = ch.request();
         unsafe {
             self.inner.regs().cr3().modify(|reg| {
                 reg.set_dmar(true);
@@ -93,7 +95,7 @@ impl<'d, T: Instance, TxDma, RxDma> Uart<'d, T, TxDma, RxDma> {
         }
         let r = self.inner.regs();
         let src = r.dr().ptr() as *mut u8;
-        ch.read(ch.request(), src, buffer).await;
+        crate::dma::read(ch, request, src, buffer).await;
         Ok(())
     }
 
diff --git a/embassy-stm32/src/usart/v2.rs b/embassy-stm32/src/usart/v2.rs
index e6e5f69db..697adf459 100644
--- a/embassy-stm32/src/usart/v2.rs
+++ b/embassy-stm32/src/usart/v2.rs
@@ -80,6 +80,7 @@ impl<'d, T: Instance, TxDma, RxDma> Uart<'d, T, TxDma, RxDma> {
         TxDma: crate::usart::TxDma<T>,
     {
         let ch = &mut self.tx_dma;
+        let request = ch.request();
         unsafe {
             self.inner.regs().cr3().modify(|reg| {
                 reg.set_dmat(true);
@@ -87,7 +88,7 @@ impl<'d, T: Instance, TxDma, RxDma> Uart<'d, T, TxDma, RxDma> {
         }
         let r = self.inner.regs();
         let dst = r.tdr().ptr() as *mut u8;
-        ch.write(ch.request(), buffer, dst).await;
+        crate::dma::write(ch, request, buffer, dst).await;
         Ok(())
     }
 
@@ -96,6 +97,7 @@ impl<'d, T: Instance, TxDma, RxDma> Uart<'d, T, TxDma, RxDma> {
         RxDma: crate::usart::RxDma<T>,
     {
         let ch = &mut self.rx_dma;
+        let request = ch.request();
         unsafe {
             self.inner.regs().cr3().modify(|reg| {
                 reg.set_dmar(true);
@@ -103,7 +105,8 @@ impl<'d, T: Instance, TxDma, RxDma> Uart<'d, T, TxDma, RxDma> {
         }
         let r = self.inner.regs();
         let src = r.rdr().ptr() as *mut u8;
-        ch.read(ch.request(), src, buffer).await;
+
+        crate::dma::read(ch, request, src, buffer).await;
         Ok(())
     }