qt-ble: add support for libdivecomputer 'set_timeout()' function

Because some BLE operations can be very slow (device and service
discovery etc), we have some rather excessive default timeout for BLE
(currently set to 12 seconds).

But once we actually have started doing IO, that long timeout can be a
big performance problem, when the libdivecomputer backend has support
for retry and packet loss.

For that reason, libdivecomputer has a 'set_timeout()' function that
allows the divecomputer backend to say how quickly it expects the dive
computer to answer before the backend will start resending packets.

Let's just implement that for the actual IO side of BLE too.  The
default timeout value remains the general BLE timeout, and this only
affects the actual IO phase, but it improves things enormously for the
case where there is packet loss at that point.

For example, on the Aqualung i770R, the timeout for packet loss ends up
now being just one second rather than the full 12 seconds of default BLE
timeout.  Which gets the retry going much faster.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 17 insertions, 2 deletions

diff --git a/core/qt-ble.cpp b/core/qt-ble.cpp
index 0ecad50c3..ba75c8472 100644
--- a/core/qt-ble.cpp
+++ b/core/qt-ble.cpp
@@ -131,6 +131,7 @@ BLEObject::BLEObject(QLowEnergyController *c, dc_user_device_t *d)
 	device = d;
 	debugCounter = 0;
 	isCharacteristicWritten = false;
+	timeout = BLE_TIMEOUT;
 }
 
 BLEObject::~BLEObject()
@@ -203,7 +204,7 @@ dc_status_t BLEObject::read(void *data, size_t size, size_t *actual)
 
 		qDebug() << QTime::currentTime() << "packet WAIT";
 
-		WAITFOR(!receivedPackets.isEmpty(), BLE_TIMEOUT);
+		WAITFOR(!receivedPackets.isEmpty(), timeout);
 		if (receivedPackets.isEmpty())
 			return DC_STATUS_IO;
 	}
@@ -516,6 +517,17 @@ static void checkThreshold()
 	}
 }
 
+/*
+ * NOTE! The 'set_timeout()' function only affects the timeout
+ * for qt_ble_read(), not for the various general BLE operations.
+ */
+dc_status_t qt_ble_set_timeout(void *io, int timeout)
+{
+	BLEObject *ble = (BLEObject *) io;
+	ble->set_timeout(timeout);
+	return DC_STATUS_SUCCESS;
+}
+
 dc_status_t qt_ble_read(void *io, void* data, size_t size, size_t *actual)
 {
 	checkThreshold();
diff --git a/core/qt-ble.h b/core/qt-ble.h
index eb028f9b9..f9600ad19 100644
--- a/core/qt-ble.h
+++ b/core/qt-ble.h
@@ -20,6 +20,7 @@ class BLEObject : public QObject
 public:
 	BLEObject(QLowEnergyController *c, dc_user_device_t *);
 	~BLEObject();
+	inline void set_timeout(int value) { timeout = value; }
 	dc_status_t write(const void* data, size_t size, size_t *actual);
 	dc_status_t read(void* data, size_t size, size_t *actual);
 
@@ -45,6 +46,7 @@ private:
 	dc_user_device_t *device;
 	unsigned int hw_credit = 0;
 	unsigned int desc_written = 0;
+	int timeout;
 
 	QList<QUuid> hwAllCharacteristics = {
 		"{00000001-0000-1000-8000-008025000000}", // HW_OSTC_BLE_DATA_RX
@@ -57,6 +59,7 @@ private:
 
 extern "C" {
 dc_status_t qt_ble_open(void **io, dc_context_t *context, const char *devaddr, dc_user_device_t *user_device);
+dc_status_t qt_ble_set_timeout(void *io, int timeout);
 dc_status_t qt_ble_read(void *io, void* data, size_t size, size_t *actual);
 dc_status_t qt_ble_write(void *io, const void* data, size_t size, size_t *actual);
 dc_status_t qt_ble_close(void *io);
diff --git a/core/qtserialbluetooth.cpp b/core/qtserialbluetooth.cpp
index 14ddacf2b..be1cda686 100644
--- a/core/qtserialbluetooth.cpp
+++ b/core/qtserialbluetooth.cpp
@@ -410,7 +410,7 @@ ble_packet_open(dc_iostream_t **iostream, dc_context_t *context, const char* dev
 	void *io = NULL;
 
 	static const dc_custom_cbs_t callbacks = {
-		NULL, /* set_timeout */
+		qt_ble_set_timeout, /* set_timeout */
 		NULL, /* set_latency */
 		NULL, /* set_break */
 		NULL, /* set_dtr */