From 4ff53e79c2c87d8ad110565dcb0cddc23598e095 Mon Sep 17 00:00:00 2001
From: Joshua Saxby <joshua.a.saxby@gmail.com>
Date: Sun, 8 Mar 2020 19:33:12 +0000
Subject: [PATCH] Add barrier() method to Pairer
---
source/TransceiverConfig.hpp | 8 ++++++++
source/main.cpp | 28 ++++++++++++++++++++++++----
2 files changed, 32 insertions(+), 4 deletions(-)
diff --git a/source/TransceiverConfig.hpp b/source/TransceiverConfig.hpp
index 9b7e56a..e93bfa2 100644
--- a/source/TransceiverConfig.hpp
+++ b/source/TransceiverConfig.hpp
@@ -53,6 +53,14 @@ namespace com_saxbophone {
* @details We currently allow a ±10% timing margin
*/
const static double DURATION_MARGIN = 0.1;
+
+ /**
+ * @brief This is the total amount of time allocated for one transmission
+ * @details This includes START/STOP bits, message bits and a bit of
+ * silence time for good measure. This is set to 600ms.
+ * @note This is the only duration in this struct to use ms for units
+ */
+ const static unsigned long TRANMISSION_WINDOW = 600;
};
};
diff --git a/source/main.cpp b/source/main.cpp
index 7dce448..258df6a 100644
--- a/source/main.cpp
+++ b/source/main.cpp
@@ -96,6 +96,29 @@ public:
}
}
+ /**
+ * @brief Returns to the caller once the amount of time since synchronisation
+ * reaches a multiple of the transmission window.
+ * @details This is intended to be used to keep both Master and Slave
+ * synchronised. Assuming their clocks were synchronised correctly, both can
+ * call this and the calls should return at near enough the same point in time.
+ */
+ void barrier() {
+ // TODO: consider allowing for a ±10% margin of error
+ unsigned long time_now = ubit.systemTime(); // what time is it now?
+ // this is how much time we have left to next sync point
+ unsigned long time_left = TransceiverConfig::TRANSMISSION_WINDOW - (
+ (time_now - this->synchronisation_timestamp) %
+ TransceiverConfig::TRANSMISSION_WINDOW
+ );
+ /*
+ * systemTime() can only sleep to 6ms resolution, so sleep to the nearest
+ * multiple of 6ms, rounded down
+ */
+ ubit.sleep((time_left / 6) * 6);
+ // TODO: consider adding busy-wait loop to increase accuracy
+ }
+
private:
bool pair_as_master() {
int pin_state = ubit.io.pin[COMMS_PIN_NUMBER].getDigitalValue();
@@ -572,11 +595,8 @@ int main() {
ubit.display.scroll("PS");
}
- // display a "P" to indicate we're paired
- ubit.display.print('P');
-
// call barrier to synchronise both master and slave
- // transceiver.barrier();
+ pairer.barrier();
/* BEGIN COMMS */
--
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