From 2e2562d8dc38844b9907e282f6c098e6ac2fd096 Mon Sep 17 00:00:00 2001
From: Adrian Figueroa <elagil@takanome.de>
Date: Tue, 26 Aug 2025 23:11:18 +0200
Subject: fix: ping-pong helper DMA direction

---
 embassy-stm32/src/dma/gpdma/linked_list.rs  | 22 +++++++++++++++++-----
 embassy-stm32/src/dma/gpdma/ringbuffered.rs |  7 ++++---
 embassy-stm32/src/dma/mod.rs                |  5 ++++-
 3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/embassy-stm32/src/dma/gpdma/linked_list.rs b/embassy-stm32/src/dma/gpdma/linked_list.rs
index 627da0055..f7c1fbbed 100644
--- a/embassy-stm32/src/dma/gpdma/linked_list.rs
+++ b/embassy-stm32/src/dma/gpdma/linked_list.rs
@@ -166,15 +166,27 @@ impl<const ITEM_COUNT: usize> Table<ITEM_COUNT> {
     /// Create a ping-pong linked-list table.
     ///
     /// This uses two linked-list items, one for each half of the buffer.
-    pub unsafe fn new_ping_pong<W: Word>(request: Request, peri_addr: *mut W, buffer: &mut [W]) -> Table<2> {
+    pub unsafe fn new_ping_pong<W: Word>(
+        request: Request,
+        peri_addr: *mut W,
+        buffer: &mut [W],
+        direction: Dir,
+    ) -> Table<2> {
         // Buffer halves should be the same length.
         let half_len = buffer.len() / 2;
         assert_eq!(half_len * 2, buffer.len());
 
-        let items = [
-            LinearItem::new_read(request, peri_addr, &mut buffer[..half_len]),
-            LinearItem::new_read(request, peri_addr, &mut buffer[half_len..]),
-        ];
+        let items = match direction {
+            Dir::MemoryToPeripheral => [
+                LinearItem::new_write(request, &mut buffer[..half_len], peri_addr),
+                LinearItem::new_write(request, &mut buffer[half_len..], peri_addr),
+            ],
+            Dir::PeripheralToMemory => [
+                LinearItem::new_read(request, peri_addr, &mut buffer[..half_len]),
+                LinearItem::new_read(request, peri_addr, &mut buffer[half_len..]),
+            ],
+        };
+
         Table::new(items)
     }
 
diff --git a/embassy-stm32/src/dma/gpdma/ringbuffered.rs b/embassy-stm32/src/dma/gpdma/ringbuffered.rs
index 55486d5cc..9ee52193b 100644
--- a/embassy-stm32/src/dma/gpdma/ringbuffered.rs
+++ b/embassy-stm32/src/dma/gpdma/ringbuffered.rs
@@ -12,7 +12,7 @@ use super::{AnyChannel, TransferOptions, STATE};
 use crate::dma::gpdma::linked_list::{RunMode, Table};
 use crate::dma::ringbuffer::{DmaCtrl, Error, ReadableDmaRingBuffer, WritableDmaRingBuffer};
 use crate::dma::word::Word;
-use crate::dma::{Channel, Request};
+use crate::dma::{Channel, Dir, Request};
 
 struct DmaCtrlImpl<'a>(Peri<'a, AnyChannel>);
 
@@ -67,7 +67,7 @@ impl<'a, W: Word> ReadableRingBuffer<'a, W> {
         options: TransferOptions,
     ) -> Self {
         let channel: Peri<'a, AnyChannel> = channel.into();
-        let table = Table::<2>::new_ping_pong::<W>(request, peri_addr, buffer);
+        let table = Table::<2>::new_ping_pong::<W>(request, peri_addr, buffer, Dir::PeripheralToMemory);
 
         Self {
             channel,
@@ -207,7 +207,7 @@ impl<'a, W: Word> WritableRingBuffer<'a, W> {
         options: TransferOptions,
     ) -> Self {
         let channel: Peri<'a, AnyChannel> = channel.into();
-        let table = Table::<2>::new_ping_pong::<W>(request, peri_addr, buffer);
+        let table = Table::<2>::new_ping_pong::<W>(request, peri_addr, buffer, Dir::MemoryToPeripheral);
 
         Self {
             channel,
@@ -222,6 +222,7 @@ impl<'a, W: Word> WritableRingBuffer<'a, W> {
         // Apply the default configuration to the channel.
         unsafe { self.channel.configure_linked_list(&self.table, self.options) };
         self.table.link(RunMode::Circular);
+
         self.channel.start();
     }
 
diff --git a/embassy-stm32/src/dma/mod.rs b/embassy-stm32/src/dma/mod.rs
index 030f906d2..5989bfd7c 100644
--- a/embassy-stm32/src/dma/mod.rs
+++ b/embassy-stm32/src/dma/mod.rs
@@ -28,10 +28,13 @@ use embassy_hal_internal::{impl_peripheral, PeripheralType};
 
 use crate::interrupt;
 
+/// The direction of a DMA transfer.
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
-enum Dir {
+pub enum Dir {
+    /// Transfer from memory to a peripheral.
     MemoryToPeripheral,
+    /// Transfer from a peripheral to memory.
     PeripheralToMemory,
 }
 
-- 
cgit