How can I tell the Rust compiler &mut [u8] has changed after a DMA operation #537
Description
Hi all!
I'm trying to force the Rust compiler to assume the contents of a &mut [u8] has changed after a DMA operation.
In the std library, calls to things like std::fs::File::read take a &mut [u8] and after the call, the contents of that slice have changed. The Rust compiler knows it can not assume the contents of that buffer after the call to read.
I need to do something similar with DMA. After a DMA operation has been completed (and hardware has written bytes to memory), the Rust compiler must assume the buf has changed.
My current solution (below) is to use asm!. Will that do the trick? Is there a more portable way?
Something like:
fn dma_read(&mut self, buf: &mut [u8]) {
// Zero out buffer
buf.fill(0);
let addr = buf.as_mut_ptr() as usize;
let len = buf.len();
// Setup DMA via MMIO
self.reg.dma_addr.set(addr);
self.reg.dma_len.set(len);
// Start DMA via MMIO
self.reg.dma_start.set(1);
// Wait for DMA to complete via MMIO
while self.reg.dma_done.get() != 1 {}
// Insert an `asm!` block to force Rust to assume `buf` has been modified
unsafe { core::arch::asm!("mov {},{}", out(reg) _, in(reg) addr) };
// Read "buf"
// At this point, how can I ensure the Rust compiler will assume buf has been modified?
}