Increase delay in Segger RTT debugging (fix #1697).

BUG=none
TEST=make

(cherry picked from commit c17fa3b)
Change-Id: I11769236fdf5cdfbe853c09f953ff59bb1ecf0df

capsules/src/segger_rtt.rs

@@ -233,9 +233,14 @@ impl<'a, A: hil::time::Alarm<'a>> uart::Transmit<'a> for SeggerRtt<'a, A> {
                     // Save the client buffer so we can pass it back with the callback.
                     self.client_buffer.replace(tx_data);
 
-                    // Start a short timer so that we get a callback and
-                    // can issue the callback to the client.
-                    let interval = (100 as u32) * <A::Frequency>::frequency() / 1000000;
+                    // Start a short timer so that we get a callback and can issue the callback to
+                    // the client.
+                    //
+                    // This heuristic interval was tested with the console capsule on a nRF52840-DK
+                    // board, passing buffers up to 1500 bytes from userspace. 100 micro-seconds
+                    // was to short, even for buffers as small as 128 bytes. 1 milli-second seems to
+                    // be reliable.
+                    let interval = (1000 as u32) * <A::Frequency>::frequency() / 1000000;
                     let tics = self.alarm.now().wrapping_add(interval);
                     self.alarm.set_alarm(tics);
                 })