Implement support for 32-bit memory access scheme. Tested on STM32C071.

Author: FeldrinH

examples/hal.rs

@@ -1,6 +1,6 @@
 //! USB peripheral
 
-use stm32_usbd::UsbPeripheral;
+use stm32_usbd::{MemoryAccess, UsbPeripheral};
 use stm32f1xx_hal::pac::{RCC, USB};
 
 pub use stm32_usbd::UsbBus;
@@ -20,7 +20,7 @@ unsafe impl UsbPeripheral for Peripheral {
     const DP_PULL_UP_FEATURE: bool = false;
     const EP_MEMORY: *const () = 0x4000_6000 as _;
     const EP_MEMORY_SIZE: usize = 512;
-    const EP_MEMORY_ACCESS_2X16: bool = false;
+    const EP_MEMORY_ACCESS: MemoryAccess = MemoryAccess::Word16x1;
 
     fn enable() {
         let rcc = unsafe { &*RCC::ptr() };

src/endpoint_memory.rs

@@ -1,140 +1,230 @@
 use crate::endpoint::NUM_ENDPOINTS;
 use crate::UsbPeripheral;
-use core::marker::PhantomData;
 use core::slice;
+use core::{marker::PhantomData, mem};
 use usb_device::{Result, UsbError};
 use vcell::VolatileCell;
 
+/// Different endpoint memory access schemes
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+#[non_exhaustive]
+pub enum MemoryAccess {
+    /// 16x1 bits per word. Each 32-bit word is accessed as one 16-bit half-word. The second half-word of the word is ignored.
+    ///
+    /// This matches the behavior of `EP_MEMORY_ACCESS_2X16 = false` from previous versions of this library.
+    Word16x1,
+    /// 16x2 bits per word. Each 32-bit word is accessed as two 16-bit half-words.
+    ///
+    /// This matches the behavior of `EP_MEMORY_ACCESS_2X16 = true` from previous versions of this library.
+    Word16x2,
+    /// 32x1 bits per word. Each 32-bit word is accessed as one 32-bit word.
+    Word32x1,
+}
+
+impl MemoryAccess {
+    /// Value to multiply offsets within the EP memory by when calculating address to read or write to.
+    #[inline(always)]
+    const fn offset_multiplier(self) -> usize {
+        match self {
+            MemoryAccess::Word16x1 => 2,
+            MemoryAccess::Word16x2 | MemoryAccess::Word32x1 => 1,
+        }
+    }
+
+    /// Size of unit used when reading and writing EP memory, in bytes.
+    #[inline(always)]
+    const fn unit_size(self) -> usize {
+        match self {
+            MemoryAccess::Word16x1 | MemoryAccess::Word16x2 => 2,
+            MemoryAccess::Word32x1 => 4,
+        }
+    }
+}
+
 pub struct EndpointBuffer<USB> {
-    mem: &'static mut [VolatileCell<u16>],
+    mem_ptr: *mut (),
+    mem_len: usize,
     marker: PhantomData<USB>,
 }
 
+unsafe impl<USB> Send for EndpointBuffer<USB> {}
+
 impl<USB: UsbPeripheral> EndpointBuffer<USB> {
     pub fn new(offset_bytes: usize, size_bytes: usize) -> Self {
-        let ep_mem_ptr = USB::EP_MEMORY as *mut VolatileCell<u16>;
-
-        let offset_words = offset_bytes >> 1;
-        let count_words = size_bytes >> 1;
-        let offset_u16_words;
-        let count_u16_words;
-        if USB::EP_MEMORY_ACCESS_2X16 {
-            offset_u16_words = offset_words;
-            count_u16_words = count_words;
-        } else {
-            offset_u16_words = offset_words * 2;
-            count_u16_words = count_words * 2;
-        };
-
-        unsafe {
-            let mem = slice::from_raw_parts_mut(ep_mem_ptr.add(offset_u16_words), count_u16_words);
-            Self {
-                mem,
-                marker: PhantomData,
-            }
-        }
-    }
+        let mem_offset_bytes = offset_bytes * USB::EP_MEMORY_ACCESS.offset_multiplier();
+        let mem_len = size_bytes * USB::EP_MEMORY_ACCESS.offset_multiplier() / USB::EP_MEMORY_ACCESS.unit_size();
 
-    #[inline(always)]
-    fn read_word(&self, index: usize) -> u16 {
-        if USB::EP_MEMORY_ACCESS_2X16 {
-            self.mem[index].get()
-        } else {
-            self.mem[index * 2].get()
+        let mem_ptr = unsafe { USB::EP_MEMORY.byte_add(mem_offset_bytes).cast_mut() };
+        Self {
+            mem_ptr,
+            mem_len,
+            marker: PhantomData,
         }
     }
 
     #[inline(always)]
-    fn write_word(&self, index: usize, value: u16) {
-        if USB::EP_MEMORY_ACCESS_2X16 {
-            self.mem[index].set(value);
-        } else {
-            self.mem[index * 2].set(value);
-        }
+    fn get_mem_slice<T>(&self) -> &mut [VolatileCell<T>] {
+        unsafe { slice::from_raw_parts_mut(self.mem_ptr.cast(), self.mem_len) }
     }
 
     pub fn read(&self, mut buf: &mut [u8]) {
-        let mut index = 0;
+        if USB::EP_MEMORY_ACCESS == MemoryAccess::Word32x1 {
+            let mem = self.get_mem_slice::<u32>();
 
-        while buf.len() >= 2 {
-            let word = self.read_word(index);
+            let mut index = 0;
 
-            buf[0] = (word & 0xff) as u8;
-            buf[1] = (word >> 8) as u8;
+            while buf.len() >= 4 {
+                let value = mem[index].get().to_ne_bytes();
+                index += USB::EP_MEMORY_ACCESS.offset_multiplier();
 
-            index += 1;
+                buf[0..4].copy_from_slice(&value);
+                buf = &mut buf[4..];
+            }
 
-            buf = &mut buf[2..];
-        }
+            if buf.len() > 0 {
+                let value = mem[index].get().to_ne_bytes();
+                buf.copy_from_slice(&value[0..buf.len()]);
+            }
+        } else {
+            let mem = self.get_mem_slice::<u16>();
+
+            let mut index = 0;
+
+            while buf.len() >= 2 {
+                let value = mem[index].get().to_ne_bytes();
+                index += USB::EP_MEMORY_ACCESS.offset_multiplier();
 
-        if buf.len() > 0 {
-            buf[0] = (self.read_word(index) & 0xff) as u8;
+                buf[0..2].copy_from_slice(&value);
+                buf = &mut buf[2..];
+            }
+
+            if buf.len() > 0 {
+                let value = mem[index].get().to_ne_bytes();
+                buf.copy_from_slice(&value[0..buf.len()]);
+            }
         }
     }
 
     pub fn write(&self, mut buf: &[u8]) {
-        let mut index = 0;
+        if USB::EP_MEMORY_ACCESS == MemoryAccess::Word32x1 {
+            let mem = self.get_mem_slice::<u32>();
+
+            let mut index = 0;
+
+            while buf.len() >= 4 {
+                let mut value = [0; 4];
+                value.copy_from_slice(&buf[0..4]);
+                buf = &buf[4..];
+                
+                mem[index].set(u32::from_ne_bytes(value));
+                index += USB::EP_MEMORY_ACCESS.offset_multiplier();
+            }
 
-        while buf.len() >= 2 {
-            let value: u16 = buf[0] as u16 | ((buf[1] as u16) << 8);
-            self.write_word(index, value);
-            index += 1;
+            if buf.len() > 0 {
+                let mut value = [0; 4];
+                value[0..buf.len()].copy_from_slice(buf);
+                mem[index].set(u32::from_ne_bytes(value));
+            }
+        } else {
+            let mem = self.get_mem_slice::<u16>();
 
-            buf = &buf[2..];
-        }
+            let mut index = 0;
 
-        if buf.len() > 0 {
-            self.write_word(index, buf[0] as u16);
+            while buf.len() >= 2 {
+                let mut value = [0; 2];
+                value.copy_from_slice(&buf[0..2]);
+                buf = &buf[2..];
+
+                mem[index].set(u16::from_ne_bytes(value));
+                index += USB::EP_MEMORY_ACCESS.offset_multiplier();
+            }
+
+            if buf.len() > 0 {
+                let mut value = [0; 2];
+                value[0..buf.len()].copy_from_slice(buf);
+                mem[index].set(u16::from_ne_bytes(value));
+            }
         }
     }
 
     pub fn offset(&self) -> u16 {
-        let buffer_address = self.mem.as_ptr() as usize;
-        let word_size = if USB::EP_MEMORY_ACCESS_2X16 { 2 } else { 4 };
-        let index = (buffer_address - USB::EP_MEMORY as usize) / word_size;
-        (index << 1) as u16
+        let offset_bytes = self.mem_ptr as usize - USB::EP_MEMORY as usize;
+        (offset_bytes / USB::EP_MEMORY_ACCESS.offset_multiplier()) as u16
     }
 
     pub fn capacity(&self) -> usize {
-        let len_words = if USB::EP_MEMORY_ACCESS_2X16 {
-            self.mem.len()
+        self.mem_len * USB::EP_MEMORY_ACCESS.unit_size() / USB::EP_MEMORY_ACCESS.offset_multiplier()
+    }
+}
+
+pub struct Field<USB> {
+    ptr: *const (),
+    marker: PhantomData<USB>,
+}
+
+impl<USB: UsbPeripheral> Field<USB> {
+    #[inline(always)]
+    pub fn get(&self) -> u16 {
+        if USB::EP_MEMORY_ACCESS == MemoryAccess::Word32x1 {
+            let unaligned_offset = self.ptr as usize & 0b11;
+            let cell: &VolatileCell<u32> = unsafe { &*self.ptr.byte_sub(unaligned_offset).cast() };
+            let value: [u16; 2] = unsafe { mem::transmute(cell.get()) };
+            value[unaligned_offset >> 1]
         } else {
-            self.mem.len() / 2
-        };
-        len_words << 1
+            let cell: &VolatileCell<u16> = unsafe { &*self.ptr.cast() };
+            cell.get()
+        }
+    }
+
+    #[inline(always)]
+    pub fn set(&self, value: u16) {
+        if USB::EP_MEMORY_ACCESS == MemoryAccess::Word32x1 {
+            let unaligned_offset = self.ptr as usize & 0b11;
+            let cell: &VolatileCell<u32> = unsafe { &*self.ptr.byte_sub(unaligned_offset).cast() };
+            let mut previous_value: [u16; 2] = unsafe { mem::transmute(cell.get()) };
+            previous_value[unaligned_offset >> 1] = value;
+            cell.set(unsafe { mem::transmute(previous_value) });
+        } else {
+            let cell: &VolatileCell<u16> = unsafe { &*self.ptr.cast() };
+            cell.set(value);
+        }
     }
 }
 
 #[repr(C)]
 pub struct BufferDescriptor<USB> {
-    ptr: *const VolatileCell<u16>,
+    ptr: *const (),
     marker: PhantomData<USB>,
 }
 
 impl<USB: UsbPeripheral> BufferDescriptor<USB> {
     #[inline(always)]
-    fn field(&self, index: usize) -> &'static VolatileCell<u16> {
-        let mul = if USB::EP_MEMORY_ACCESS_2X16 { 1 } else { 2 };
-        unsafe { &*(self.ptr.add(index * mul)) }
+    fn field(&self, index: usize) -> Field<USB> {
+        let mul = USB::EP_MEMORY_ACCESS.offset_multiplier();
+        let ptr = unsafe { self.ptr.byte_add(index * 2 * mul) };
+        Field {
+            ptr,
+            marker: PhantomData,
+        }
     }
 
     #[inline(always)]
-    pub fn addr_tx(&self) -> &'static VolatileCell<u16> {
+    pub fn addr_tx(&self) -> Field<USB> {
         self.field(0)
     }
 
     #[inline(always)]
-    pub fn count_tx(&self) -> &'static VolatileCell<u16> {
+    pub fn count_tx(&self) -> Field<USB> {
         self.field(1)
     }
 
     #[inline(always)]
-    pub fn addr_rx(&self) -> &'static VolatileCell<u16> {
+    pub fn addr_rx(&self) -> Field<USB> {
         self.field(2)
     }
 
     #[inline(always)]
-    pub fn count_rx(&self) -> &'static VolatileCell<u16> {
+    pub fn count_rx(&self) -> Field<USB> {
         self.field(3)
     }
 }
@@ -167,14 +257,11 @@ impl<USB: UsbPeripheral> EndpointMemoryAllocator<USB> {
     }
 
     pub fn buffer_descriptor(index: u8) -> BufferDescriptor<USB> {
-        let mul = if USB::EP_MEMORY_ACCESS_2X16 { 1 } else { 2 };
-
-        unsafe {
-            let ptr = (USB::EP_MEMORY as *const VolatileCell<u16>).add((index as usize) * 4 * mul);
-            BufferDescriptor {
-                ptr,
-                marker: Default::default(),
-            }
+        let mul = USB::EP_MEMORY_ACCESS.offset_multiplier();
+        let ptr = unsafe { USB::EP_MEMORY.byte_add((index as usize) * 8 * mul).cast() };
+        BufferDescriptor {
+            ptr,
+            marker: Default::default(),
         }
     }
 }

src/lib.rs

@@ -10,6 +10,7 @@ mod endpoint;
 mod endpoint_memory;
 mod registers;
 pub use crate::bus::UsbBus;
+pub use crate::endpoint_memory::MemoryAccess;
 
 mod pac;
 
@@ -31,9 +32,8 @@ pub unsafe trait UsbPeripheral: Send + Sync {
 
     /// Endpoint memory access scheme
     ///
-    /// Check Reference Manual for details.
-    /// Set to `true` if "2x16 bits/word" access scheme is used, otherwise set to `false`.
-    const EP_MEMORY_ACCESS_2X16: bool;
+    /// See `MemoryAccess` enum for more details. Check Reference Manual to determine the correct access scheme to use.
+    const EP_MEMORY_ACCESS: MemoryAccess;
 
     /// Enables USB device on its peripheral bus
     fn enable();