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Fix one byte UART transmissions for lowrisc (maybe) #1817

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May 11, 2020
Merged

Fix one byte UART transmissions for lowrisc (maybe) #1817

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51 changes: 22 additions & 29 deletions chips/lowrisc/src/uart.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -175,6 +175,14 @@ impl Uart<'a> {
let len = self.tx_len.get();

if idx < len {
// If we are going to transmit anything, we first need to enable the
// TX interrupt. This ensures that we will get an interrupt, where
// we can either call the callback from, or continue transmitting
// bytes.
self.enable_tx_interrupt();

// Read from the transmit buffer and send bytes to the UART hardware
// until either the buffer is empty or the UART hardware is full.
self.tx_buffer.map(|tx_buf| {
let tx_len = len - idx;

Expand All @@ -187,33 +195,6 @@ impl Uart<'a> {
self.tx_index.set(tx_idx + 1)
}
});

// If the FIFO started empty above, when the first character was written, it would have
// been immediately dispatched to the shift register, latching the TX_EMPTY state.
// That should be cleared before enabling the interrupt, so a subsequent empty state
// will latch the state transition again.
regs.intr_state.write(intr::tx_empty::SET);

// With data queued, (re)enable the TX interrupt if the FIFO is not empty
if !regs.status.is_set(status::txempty) {
self.enable_tx_interrupt();
if !regs.status.is_set(status::txempty) {
// Assuming the FIFO stayed non-empty while the interrupt was being enabled,
// our work here is done
return;
} else {
// Otherwise, turn off the interrupt and handle below
self.disable_tx_interrupt();
}
}
}

if self.tx_index.get() == self.tx_len.get() {
self.tx_client.map(|client| {
self.tx_buffer.take().map(|tx_buf| {
client.transmitted_buffer(tx_buf, self.tx_len.get(), ReturnCode::SUCCESS);
});
});
}
}

Expand All @@ -223,7 +204,19 @@ impl Uart<'a> {

if intrs.is_set(intr::tx_empty) {
self.disable_tx_interrupt();
self.tx_progress();

if self.tx_index.get() == self.tx_len.get() {
// We sent everything to the UART hardware, now from an
// interrupt callback we can issue the callback.
self.tx_client.map(|client| {
self.tx_buffer.take().map(|tx_buf| {
client.transmitted_buffer(tx_buf, self.tx_len.get(), ReturnCode::SUCCESS);
});
});
} else {
// We have more to transmit, so continue in tx_progress().
self.tx_progress();
}
} else if intrs.is_set(intr::rx_watermark) {
self.disable_rx_interrupt();
// TODO: real RX processing
Expand Down Expand Up @@ -268,7 +261,7 @@ impl hil::uart::Transmit<'a> for Uart<'a> {
tx_data: &'static mut [u8],
tx_len: usize,
) -> (ReturnCode, Option<&'static mut [u8]>) {
if tx_len == 0 {
if tx_len == 0 || tx_len > tx_data.len() {
(ReturnCode::ESIZE, Some(tx_data))
} else if self.tx_buffer.is_some() {
(ReturnCode::EBUSY, Some(tx_data))
Expand Down