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HAL_PX4: added a read buffer to the UART driver

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this lowers the average cost of reading bytes by a large amount, and
prevents the GPS driver from chewing lots of time.
This commit is contained in:
Andrew Tridgell 2013-01-22 10:34:04 +11:00
parent f303554259
commit 18cfd29f2f
2 changed files with 43 additions and 5 deletions
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42
libraries/AP_HAL_PX4/UARTDriver.cpp
View File

@ -37,6 +37,7 @@ void PX4UARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
return;
}
_initialised = true;
}
if (b != 0) {
@ -48,6 +49,15 @@ void PX4UARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
t.c_oflag &= ~ONLCR;
tcsetattr(_fd, TCSANOW, &t);
}
if (rxS != 0 && rxS != _readbuf_size) {
_readbuf_size = rxS;
if (_readbuf != NULL) {
free(_readbuf);
}
_readbuf = (uint8_t *)malloc(_readbuf_size);
_readbuf_ofs = 0;
_readbuf_count = 0;
}
}
void PX4UARTDriver::begin(uint32_t b)
@ -101,6 +111,13 @@ int16_t PX4UARTDriver::available() {
if (!_initialised) {
return 0;
}
if (_readbuf_count != 0) {
// avoid the cost of the ioctl if possible. This means
// we are giving a lower response than is real, but
// this saves a lot of ioctl system calls, which are
// quite expensive (especially in the GPS driver)
return (int16_t)_readbuf_count;
}
if (ioctl(_fd, FIONREAD, (long unsigned int)&ret) == 0 && ret > 0) {
if (ret > 90) ret = 90;
return ret;
@ -121,13 +138,28 @@ int16_t PX4UARTDriver::txspace() {
}
int16_t PX4UARTDriver::read() {
if (available() > 0) {
uint8_t c;
if (::read(_fd, &c, 1) == 1) {
return c;
uint8_t c;
if (!_initialised || _readbuf == NULL) {
return -1;
}
if (_readbuf_count == 0) {
// refill the read buffer
int16_t avail = available();
if (avail > 0) {
int n = ::read(_fd, _readbuf, _readbuf_size);
if (n > 0) {
_readbuf_count = n;
_readbuf_ofs = 0;
}
}
}
return -1;
if (_readbuf_count == 0) {
return -1;
}
c = _readbuf[_readbuf_ofs];
_readbuf_ofs++;
_readbuf_count--;
return c;
}
/* PX4 implementations of Print virtual methods */

6
libraries/AP_HAL_PX4/UARTDriver.h
View File

@ -44,6 +44,12 @@ private:
int _fd;
bool _nonblocking_writes;
void _vdprintf(int fd, const char *fmt, va_list ap);
// we keep a small read buffer to lower the cost of ::read() system calls
uint16_t _readbuf_size;
uint8_t *_readbuf;
uint16_t _readbuf_count;
uint16_t _readbuf_ofs;
};
#endif // __AP_HAL_PX4_UARTDRIVER_H__