From f87a087540b8a6fba8cee728e11861b7799645a7 Mon Sep 17 00:00:00 2001
From: Joshua Saxby <joshua.a.saxby@gmail.com>
Date: Thu, 5 Mar 2020 18:47:51 +0000
Subject: [PATCH] Implemented Slave pair method This completes the pairing
functionality
---
source/main.cpp | 89 +++++++++++++++++++++++++++++++++----------------
1 file changed, 60 insertions(+), 29 deletions(-)
diff --git a/source/main.cpp b/source/main.cpp
index ded7c11..047622c 100755
--- a/source/main.cpp
+++ b/source/main.cpp
@@ -115,37 +115,12 @@ private:
}
// successful execution continues here
// wait for the pin to stay LO for 500ms
- unsigned long start_time = ubit.systemTime();
- unsigned long now_time = start_time;
- do {
- /*
- * NOTE: this is a busy wait loop with no sleep()
- * this is okay as we're deliberately allowing this function to
- * block the entire system, it's documented as such and we also can
- * only sleep to a 6ms precision, but we want to time as accurately
- * as possible for the pairing process
- */
- now_time = ubit.systemTime();
- pin_state = ubit.io.pin[COMMS_PIN_NUMBER].getDigitalValue();
- } while (pin_state == 0 and (now_time - start_time) < 500);
+ unsigned long start_time, now_time;
+ this->busy_wait_on_pin(0, 500, pin_state, start_time, now_time);
// check to make sure we didn't break out of the loop because of HI pin
if (pin_state != 0) return false;
// there's definitely no-one else transmitting on the line, now we transmit
- start_time = ubit.systemTime();
- now_time = start_time;
- ubit.io.pin[COMMS_PIN_NUMBER].setDigitalValue(1);
- // wait 500ms
- do {
- /*
- * NOTE: as with the previous loop, this is a busy wait loop
- * it's particularly important that this one is accurately timed,
- * as we expect ourself and the Slave to synchronise clocks on the
- * falling edge of this pulse we send
- */
- now_time = ubit.systemTime();
- } while ((now_time - start_time) < 500);
- // bring line LO
- ubit.io.pin[COMMS_PIN_NUMBER].setDigitalValue(0);
+ this->busy_wait_drive_pin(500, start_time, now_time);
// now_time is the clock synchronisation timestamp
this->synchronisation_timestamp = now_time;
// now, wait up to 100ms for a reply from the Slave
@@ -164,7 +139,62 @@ private:
return this->await_synchronisation();
}
- bool pair_as_slave();
+ bool pair_as_slave() {
+ // check the pin can read digital values
+ int pin_state = ubit.io.pin[COMMS_PIN_NUMBER].getDigitalValue();
+ if (pin_state == MICROBIT_NOT_SUPPORTED) return false; // oh no, it can't
+ // otherwise, it can read digital values
+ // now, wait up to 10000ms for Master to drive the line HI
+ unsigned long start_time, end_time;
+ this->busy_wait_on_pin(0, 10000, pin_state, start_time, end_time);
+ // clarify the loop ended because pin is now indeed HI
+ if (pin_state != 1) return false; // we timed out
+ // otherwise, line is HI, wait for it to stay that way at least 450ms
+ this->busy_wait_on_pin(1, 450, pin_state, start_time, end_time);
+ // clarify the loop ended because timeout occurred (pin should be HI)
+ if (pin_state != 1) return false; // pin went LO, that's not correct
+ // wait up to 100 more ms for line to go LO
+ this->busy_wait_on_pin(1, 100, pin_state, start_time, end_time);
+ // if line is still HI, then it's overrun
+ if (pin_state == 1) return false;
+ // otherwise, it's now our turn to bring the line HI
+ // the most recent end_time is also the sync point, store that first
+ this->synchronisation_timestamp = end_time;
+ // drive line HI
+ this->busy_wait_drive_pin(500, start_time, end_time);
+ // now we just need to await synchronisation
+ return this->await_synchronisation();
+ }
+
+ /**
+ * @brief Drives the comms pin HI and performs a busy-wait loop for a given
+ * duration, before driving the pin LO again.
+ * @param duration length of time in ms to drive the pin HI for
+ * @param start_time[out] system timestamp (ms) that the pin went HI
+ * @param end_time[out] system timestamp (ms) that the pin went LO
+ */
+ void busy_wait_drive_pin(
+ unsigned long duration
+ unsigned long& start_time,
+ unsigned long& end_time
+ ) {
+ start_time = ubit.systemTime();
+ end_time = start_time;
+ ubit.io.pin[COMMS_PIN_NUMBER].setDigitalValue(1);
+ // wait for specified duration
+ do {
+ /*
+ * NOTE: this is a busy wait loop with no sleep()
+ * this is okay as we're deliberately allowing this function to
+ * block the entire system, it's documented as such and we also can
+ * only sleep to a 6ms precision, but we want to time as accurately
+ * as possible
+ */
+ end_time = ubit.systemTime();
+ } while ((end_time - start_time) < duration);
+ // bring line LO
+ ubit.io.pin[COMMS_PIN_NUMBER].setDigitalValue(0);
+ }
/**
* @brief Performs a busy-wait loop, continuously checking the comms pin
@@ -224,6 +254,7 @@ private:
do {
now_time = ubit.systemTime();
} while (now_time < sync_time);
+ return true; // at this point, now both Master and Slave are synchronised
}
unsigned long synchronisation_timestamp;
--
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