static DMA ctrl block placement

examples/simple/examples/dma.rs

@@ -17,11 +17,14 @@ use va416xx_hal::{
     prelude::*,
 };
 
-// Place the DMA control block in SRAM1
-const DMA_CTRL_BLOCK_ADDR: u32 = 0x2000_0000;
 static DMA_DONE_FLAG: Mutex<Cell<bool>> = Mutex::new(Cell::new(false));
 static DMA_ACTIVE_FLAG: Mutex<Cell<bool>> = Mutex::new(Cell::new(false));
 
+// Place the DMA control block into SRAM1 statically. This section needs to be defined in
+// memory.x
+#[link_section = ".sram1"]
+static mut DMA_CTRL_BLOCK: DmaCtrlBlock = DmaCtrlBlock::new();
+
 #[entry]
 fn main() -> ! {
     rtt_init_print!();
@@ -35,9 +38,11 @@ fn main() -> ! {
         .xtal_n_clk_with_src_freq(peb1::EXTCLK_FREQ)
         .freeze(&mut dp.sysconfig)
         .unwrap();
-    let dma_ctrl_block =
+    // Safety: The DMA control block has an alignment rule of 128 and we constructed it directly
-        DmaCtrlBlock::new_at_addr(DMA_CTRL_BLOCK_ADDR).expect("error creating DMA control block");
+    // statically.
-    let dma = Dma::new(&mut dp.sysconfig, dp.dma, DmaCfg::default(), dma_ctrl_block)
+    let dma = Dma::new(&mut dp.sysconfig, dp.dma, DmaCfg::default(), unsafe {
+        core::ptr::addr_of_mut!(DMA_CTRL_BLOCK)
+    })
     .expect("error creating DMA");
     let (mut dma0, _, _, _) = dma.split();
     let mut delay_ms = CountdownTimer::new(&mut dp.sysconfig, dp.tim0, &clocks);

va416xx-hal/src/dma.rs

@@ -118,22 +118,42 @@ pub struct DmaChannelControl {
     padding: u32,
 }
 
+impl DmaChannelControl {
+    const fn new() -> Self {
+        Self {
+            src_end_ptr: 0,
+            dest_end_ptr: 0,
+            cfg: ChannelConfig(0),
+            padding: 0,
+        }
+    }
+}
 impl Default for DmaChannelControl {
     fn default() -> Self {
-        Self {
+        Self::new()
-            src_end_ptr: Default::default(),
-            dest_end_ptr: Default::default(),
-            cfg: ChannelConfig(0),
-            padding: Default::default(),
-        }
     }
 }
 #[repr(C)]
+#[repr(align(128))]
 pub struct DmaCtrlBlock {
     pub pri: [DmaChannelControl; 4],
     pub alt: [DmaChannelControl; 4],
 }
 
+impl DmaCtrlBlock {
+    pub const fn new() -> Self {
+        Self {
+            pri: [DmaChannelControl::new(); 4],
+            alt: [DmaChannelControl::new(); 4],
+        }
+    }
+}
+impl Default for DmaCtrlBlock {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl DmaCtrlBlock {
     /// This function creates a DMA control block at the specified memory address.
     ///
@@ -145,15 +165,7 @@ impl DmaCtrlBlock {
             return Err(InvalidCtrlBlockAddr);
         }
         let ctrl_block_ptr = addr as *mut DmaCtrlBlock;
-        unsafe {
+        unsafe { core::ptr::write(ctrl_block_ptr, DmaCtrlBlock::default()) }
-            core::ptr::write(
-                ctrl_block_ptr,
-                DmaCtrlBlock {
-                    pri: [DmaChannelControl::default(); 4],
-                    alt: [DmaChannelControl::default(); 4],
-                },
-            )
-        }
         Ok(ctrl_block_ptr)
     }
 }
@@ -388,7 +400,13 @@ impl DmaChannel {
 impl Dma {
     /// Create a new DMA instance.
     ///
-    /// You can use [DmaCtrlBlock::new_at_addr] to create the DMA control block at a specific address.
+    /// You can also place the [DmaCtrlBlock] statically using a global static mutable
+    /// instance and the [DmaCtrlBlock::new] const constructor This also allows to place the control
+    /// block in a memory section using the [link_section](https://doc.rust-lang.org/reference/abi.html#the-link_section-attribute)
+    /// attribute and then creating a mutable pointer to it using [core::ptr::addr_of_mut].
+    ///
+    /// Alternatively, the [DmaCtrlBlock::new_at_addr] function can be used to create the DMA
+    /// control block at a specific address.
     pub fn new(
         syscfg: &mut pac::Sysconfig,
         dma: pac::Dma,