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gps: reduce delay by reducing the sleep time

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This uses now the same sleep time logic as mavlink, depending on the
baudrate.

CPU usage on a Pixracer for different sleep times:

#num reads/sec    sleep time         CPU usage
17-18             2.8ms              0.233-0.31% (this PR)
12                5ms                0.155-0.3%
9-10              10ms               0.155-0.233%
6                 20ms               0.155-0.233% (previous)
This commit is contained in:
Beat Küng
2018-10-02 14:14:10 +02:00
committed by Lorenz Meier
parent 979e8ad28b
commit cef6cf96f8
1 changed files with 9 additions and 6 deletions
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src/drivers/gps/gps.cpp
+9 -6
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@@ -90,7 +90,6 @@
#define TIMEOUT_5HZ 500
#define RATE_MEASUREMENT_PERIOD 5000000
#define GPS_WAIT_BEFORE_READ 20 // ms, wait before reading to save read() calls
/* struct for dynamic allocation of satellite info data */
@@ -381,17 +380,21 @@ int GPS::pollOrRead(uint8_t *buf, size_t buf_length, int timeout)
* If we have all requested data available, read it without waiting.
* If more bytes are available, we'll go back to poll() again.
*/
const unsigned character_count = 32; // minimum bytes that we want to read
unsigned baudrate = _baudrate == 0 ? 115200 : _baudrate;
const unsigned sleeptime = character_count * 1000000 / (baudrate / 10);
#ifdef __PX4_NUTTX
int err = 0;
int bytesAvailable = 0;
err = ioctl(_serial_fd, FIONREAD, (unsigned long)&bytesAvailable);
int bytes_available = 0;
err = ioctl(_serial_fd, FIONREAD, (unsigned long)&bytes_available);
if ((err != 0) || (bytesAvailable < (int)buf_length)) {
usleep(GPS_WAIT_BEFORE_READ * 1000);
if (err != 0 || bytes_available < (int)character_count) {
usleep(sleeptime);
}
#else
usleep(GPS_WAIT_BEFORE_READ * 1000);
usleep(sleeptime);
#endif
ret = ::read(_serial_fd, buf, buf_length);