Add DMAMUX support

[ijager]

WIP

This PR will address #12. Integrate support for DMAMUX into the DMA driver.

Steps to use DMA:

DMA peripheral init

Only needs RCC

• reset peripheral

• enable DMA clock

---

DMA Channel configure

• Pick DMA channel (1..5, 1..7) (Note: DMAMUX starts at zero)

• Configure DMAMUX dmareq_id with correct index value.

• Configure DMA channel (dma ccr register):

• Write peripheral register in DMA

• Configure memory buffer address (cparx) and length (cndtrx)

• Enable DMA mode in peripheral

---

start transfer

• (update buffer addresses)
• enable dma channel (ccr reg -> enable bit)

---

Let's model the DMA driver on stm32f3xx-hal.

Perhaps the DMA Target trait implementations should also configure the DMAMUX, since the peripheral implementation knows which DMAMUX index to set.

/// Trait implemented by DMA targets.
pub trait Target {
    /// Enable DMA on the target
    fn enable_dma(&mut self) {}
    /// Disable DMA on the target
    fn disable_dma(&mut self) {}
}

[andresv]

Super!

Yes, I also think that Target should configure DMAMUX because index is known.

[ijager]

I have something working, but it depends on stm32-rs/stm32-rs#408

I added the link_dma method in the dma::Target trait

/// Trait implemented by DMA targets.
pub trait Target {

    /// Connect dmamux channel to dma channel and peripheral
    ///
    /// The implementation should call
    /// dma_ch.select_peripheral(DmaMuxIndex::XXX)
    /// with the correct DmaMuxIndex for XXX
    fn link_dma<C: Channel>(&mut self, dma_ch: &mut C);

    /// Enable DMA on the target
    fn enable_dma(&mut self) {}
    /// Disable DMA on the target
    fn disable_dma(&mut self) {}
}

Which needs to be implemented by the peripheral driver that wants to use DMA:

impl<Config> dma::Target for Rx<$USARTX, Config> {

    fn link_dma<C: dma::Channel>(&mut self, dma_ch: &mut C) {
        dma_ch.select_peripheral(DmaMuxIndex::USART1_RX)
     }
}

Example of how to use it:

    let (mut tx, _rx) = usart1.split();

    let mut dma = dp.DMA.split(&mut rcc, dp.DMAMUX);

    let usart = unsafe { &(*stm32::USART1::ptr()) };
    let tx_data_register_addr = &usart.tdr as *const _ as u32;
    let tx_dma_buf_addr : u32 = tx_buffer.as_ptr() as u32;

    dma.ch1.set_direction(dma::Direction::FromMemory);
    dma.ch1.set_memory_address(tx_dma_buf_addr, true);
    dma.ch1.set_peripheral_address(tx_data_register_addr, false);
    dma.ch1.set_transfer_length(tx_buffer.len() as u16);

    tx.link_dma(&mut dma.ch1);
    tx.enable_dma();
    dma.ch1.enable();

What do you think?

[andresv]

I think it is okay. My only concern is about method link_dma name.
Maybe this is more intuitive:

 tx.use_channel(&mut dma.ch1);
 tx.enable_dma();
 dma.ch1.enable();

Or actually it is other way around, we do not want to use channel, channel wants to use peripheral:

 tx.select_peripheral(&mut dma.ch1);
 tx.enable_dma();
 dma.ch1.enable()

But this is also misleading. Basically we would like to configure which peripheral a channel should use, tx has other methods so actually yes _dma should be in this name.

 tx.assign_to_dma(&mut dma.ch1);
// or
 tx.configure_dma(&mut dma.ch1);
 tx.enable_dma();
 dma.ch1.enable();

I think this method name should be more clear, but I do not have a good proposal either. Maybe you have some more ideas how to name it?

[ijager]

perhaps

tx.use_dma_channel(&mut dma.ch1);

[andresv]

What if:

dma.ch1.set_transfer_length(tx_buffer.len() as u16);
dma.ch1.select_peripheral(tx.dmamux());
tx.enable_dma();
dma.ch1.enable();

[ijager]

So it is

tx.use_dma_channel(&mut dma.ch1);
// vs
dma.ch1.select_peripheral(tx.dmamux());

I like your suggestion since we're configuring dma. Let me try it in the next commit.

[andresv]

You can do this:

let mut tx_buffer: [u8; 16] = *b"Hello with DMA!\n";

[ijager]

I think this can be merged, unless there are other issues?