Hold onto source/destination; Remove UB from example

Author: astapleton

examples/dma.rs

@@ -7,12 +7,52 @@ mod utilities;
 use cortex_m::singleton;
 use cortex_m_rt::entry;
 use cortex_m_semihosting::debug;
+use embedded_dma::{ReadBuffer, WriteBuffer};
 use stm32h5xx_hal::{
-    gpdma::{config::transform::*, DmaConfig, DmaTransfer},
+    gpdma::{config::transform::*, DmaConfig, DmaTransfer, Word},
     pac,
     prelude::*,
 };
 
+// Buffer is used to manage a reference to a static buffer returned by the cortex_m::singleton!
+// macro and which can be with the DmaTransfer API (which requires passing ReadBuffer and
+// WriteBuffer implementations by value) and then used to access the buffer after the transfer has
+// completed.
+struct Buffer<T: Word + 'static, const N: usize> {
+    data: &'static mut [T; N],
+}
+
+impl<T, const N: usize> Buffer<T, N>
+where
+    T: Word + 'static,
+{
+    fn new(data: &'static mut [T; N]) -> Self {
+        Self { data }
+    }
+}
+
+unsafe impl<T, const N: usize> ReadBuffer for &Buffer<T, N>
+where
+    T: Word + 'static,
+{
+    type Word = T;
+
+    unsafe fn read_buffer(&self) -> (*const Self::Word, usize) {
+        (self.data.as_ptr(), N)
+    }
+}
+
+unsafe impl<T, const N: usize> WriteBuffer for &mut Buffer<T, N>
+where
+    T: Word + 'static,
+{
+    type Word = T;
+
+    unsafe fn write_buffer(&mut self) -> (*mut Self::Word, usize) {
+        (self.data.as_mut_ptr(), N)
+    }
+}
+
 #[entry]
 fn main() -> ! {
     utilities::logger::init();
@@ -31,90 +71,109 @@ fn main() -> ! {
     log::info!("u8 to u8");
     let src =
         singleton!(: [u8; 40] = core::array::from_fn(|i| i as u8)).unwrap();
+
+    let src_buffer = Buffer::new(src);
     let dest = singleton!(: [u8; 40] = [0u8; 40]).unwrap();
-    let source_copy = unsafe { &*(src.as_ptr() as *const [u8; 40]) };
-    let dest_copy = unsafe { &*(dest.as_ptr() as *const [u8; 40]) };
+    let mut dest_buffer = Buffer::new(dest);
 
     let mut channel = channels.0;
     let config = DmaConfig::new();
-    let mut transfer =
-        DmaTransfer::memory_to_memory(config, &mut channel, src, dest);
+    let mut transfer = DmaTransfer::memory_to_memory(
+        config,
+        &mut channel,
+        &src_buffer,
+        &mut dest_buffer,
+    );
     transfer.start().unwrap();
     transfer.wait_for_transfer_complete().unwrap();
-    assert_eq!(source_copy, dest_copy);
+    assert_eq!(src_buffer.data, dest_buffer.data);
 
     log::info!("u32 to u32 with data transform");
     let src = singleton!(: [u32; 10] = [0x12345678u32; 10]).unwrap();
     let dest = singleton!(: [u32; 10] = [0u32; 10]).unwrap();
-
-    let dest_copy = unsafe { &*(dest.as_ptr() as *const [u32; 10]) };
+    let mut dest_buffer = Buffer::new(dest);
 
     let config = DmaConfig::new().with_data_transform(
         DataTransform::builder()
             .swap_destination_half_words()
             .swap_destination_half_word_byte_order(),
     );
 
-    let mut transfer =
-        DmaTransfer::memory_to_memory(config, &mut channel, src, dest);
+    let mut transfer = DmaTransfer::memory_to_memory(
+        config,
+        &mut channel,
+        src,
+        &mut dest_buffer,
+    );
 
     transfer.start().unwrap();
     transfer.wait_for_transfer_complete().unwrap();
     let expected = [0x78563412; 10];
-    assert_eq!(expected, *dest_copy);
+    assert_eq!(expected, *dest_buffer.data);
 
     log::info!("u32 to u16 with truncate");
     let src = singleton!(: [u32; 10] = [0x12345678u32; 10]).unwrap();
     let dest = singleton!(: [u16; 20] = [0u16; 20]).unwrap();
-    let dest_copy = unsafe { &*(dest.as_ptr() as *const [u16; 20]) };
+    let mut dest_buffer = Buffer::new(dest);
+
     let config = DmaConfig::new().with_data_transform(
         DataTransform::builder().left_align_right_truncate(),
     );
-    let mut transfer =
-        DmaTransfer::memory_to_memory(config, &mut channel, src, dest);
+    let mut transfer = DmaTransfer::memory_to_memory(
+        config,
+        &mut channel,
+        src,
+        &mut dest_buffer,
+    );
 
     transfer.start().unwrap();
     transfer.wait_for_transfer_complete().unwrap();
     let expected = [0x1234; 10];
-    assert_eq!(expected, (*dest_copy)[0..10]);
+    assert_eq!(expected, (*dest_buffer.data)[0..10]);
 
     log::info!("u32 to u8 with unpack");
     let src = singleton!(: [u32; 10] = [0x12345678u32; 10]).unwrap();
     let dest = singleton!(: [u8; 40] = [0u8; 40]).unwrap();
-
-    let dest_copy = unsafe { &*(dest.as_ptr() as *const [u8; 40]) };
+    let mut dest_buffer = Buffer::new(dest);
 
     let config =
         DmaConfig::new().with_data_transform(DataTransform::builder().unpack());
-    let mut transfer =
-        DmaTransfer::memory_to_memory(config, &mut channel, src, dest);
+    let mut transfer = DmaTransfer::memory_to_memory(
+        config,
+        &mut channel,
+        src,
+        &mut dest_buffer,
+    );
 
     transfer.start().unwrap();
     transfer.wait_for_transfer_complete().unwrap();
     let expected = [0x78, 0x56, 0x34, 0x12];
-    assert_eq!(expected, (*dest_copy)[0..4]);
-    assert_eq!(expected, (*dest_copy)[36..40]);
+    assert_eq!(expected, (*dest_buffer.data)[0..4]);
+    assert_eq!(expected, (*dest_buffer.data)[36..40]);
 
     log::info!("u8 to u32 with pack");
     let src = singleton!(: [u8; 40] = [0u8; 40]).unwrap();
     let dest = singleton!(: [u32; 10] = [0u32; 10]).unwrap();
+    let mut dest_buffer = Buffer::new(dest);
 
     for chunk in src.chunks_mut(4) {
         chunk.copy_from_slice(&[0x78, 0x56, 0x34, 0x12]);
     }
 
-    let dest_copy = unsafe { &*(dest.as_ptr() as *const [u32; 10]) };
-
     let config =
         DmaConfig::new().with_data_transform(DataTransform::builder().pack());
-    let mut transfer =
-        DmaTransfer::memory_to_memory(config, &mut channel, src, dest);
+    let mut transfer = DmaTransfer::memory_to_memory(
+        config,
+        &mut channel,
+        src,
+        &mut dest_buffer,
+    );
 
     transfer.start().unwrap();
     transfer.wait_for_transfer_complete().unwrap();
     let expected = [0x12345678; 10];
-    assert_eq!(expected, (*dest_copy));
-    assert_eq!(expected, (*dest_copy));
+    assert_eq!(expected, (*dest_buffer.data));
+    assert_eq!(expected, (*dest_buffer.data));
 
     log::info!("All tests passed!");
     loop {