[otlib] Adjust the UART pacing
Add an explicit sleep rather than using an I/O poll with timeout.
Signed-off-by: Chris Frantz <cfrantz@google.com>
diff --git a/sw/host/opentitanlib/src/transport/common/uart.rs b/sw/host/opentitanlib/src/transport/common/uart.rs
index e8ef564..eecdf3d 100644
--- a/sw/host/opentitanlib/src/transport/common/uart.rs
+++ b/sw/host/opentitanlib/src/transport/common/uart.rs
@@ -144,7 +144,7 @@
// If flow control is enabled, read data from the input stream and
// process the flow control chars.
while self.flow_control.get() != FlowControl::None {
- self.read_worker(pacing)?;
+ self.read_worker(Duration::ZERO)?;
// If we're ok to send, then break out of the flow-control loop and send the data.
if self.flow_control.get() == FlowControl::Resume {
break;
@@ -154,6 +154,11 @@
.borrow_mut()
.write_all(std::slice::from_ref(b))
.context("UART write error")?;
+ // Sleep one uart character time after writing to the uart to pace characters into the
+ // usb-serial device so that we don't fill any device-internal buffers. The CW310 (for
+ // example) appears to have a large internal buffer that will keep transmitting to OT
+ // even if an XOFF is sent.
+ std::thread::sleep(pacing);
}
Ok(())
}
