fpga-boss: Add escape (Ctrl-T+B) for sending break sequence.

This is useful for collecting more diagnostics from a misbehaving
kernel.

ci-tools/fpga-boss/src/ftdi_uart.rs

@@ -1,6 +1,9 @@
 // Licensed under the Apache-2.0 license
 
-use std::io::{self, ErrorKind};
+use std::{
+    io::{self, ErrorKind},
+    time::Duration,
+};
 
 use libftdi1_sys::{ftdi_bits_type, ftdi_interface, ftdi_parity_type, ftdi_stopbits_type};
 use std::cell::RefCell;
@@ -22,6 +25,24 @@ pub struct FtdiUartReaderBlocking {
 pub struct FtdiUartWriter {
     ftdi: Rc<RefCell<FtdiCtx>>,
 }
+impl FtdiUartWriter {
+    pub fn send_break(&self) -> anyhow::Result<()> {
+        const BREAK_TIME: Duration = Duration::from_micros(100);
+
+        let mut ftdi = self.ftdi.borrow_mut();
+        ftdi.set_bitmode(0x01, BitMode::BitBang)?;
+        ftdi.write_all_data(&[0x00])?;
+        std::thread::sleep(BREAK_TIME);
+        ftdi.set_bitmode(0x01, BitMode::Reset)?;
+        ftdi.set_baudrate(115200)?;
+        ftdi.set_line_property(
+            ftdi_bits_type::BITS_8,
+            ftdi_stopbits_type::STOP_BIT_1,
+            ftdi_parity_type::NONE,
+        )?;
+        Ok(())
+    }
+}
 
 pub fn open(
     port_path: UsbPortPath,

ci-tools/fpga-boss/src/main.rs

@@ -251,6 +251,9 @@ fn main_impl() -> anyhow::Result<()> {
                 let mut stdin_len = tty::read_stdin_nonblock(&mut stdin_buf)?;
                 escaper.process(&mut stdin_buf, &mut stdin_len, |ch| match ch {
                     b'q' | b'Q' => alive = false,
+                    b'b' | b'B' => {
+                        uart_tx.send_break().unwrap();
+                    }
                     ch => println!(
                         "Unknown escape sequence: Ctrl-T + {:?}",
                         char::from_u32(ch.into()).unwrap_or('?')