HAL_PX4: added per-device perf counter for I2C devices

libraries/AP_HAL_PX4/I2CDevice.cpp

@@ -87,18 +87,26 @@ I2CDevice::I2CDevice(uint8_t bus, uint8_t address) :
 {
     set_device_bus(_px4dev.map_bus_number(bus));
     set_device_address(address);
+    asprintf(&pname, "I2C:%u:%02x",
+             (unsigned)bus, (unsigned)address);
+    perf = perf_alloc(PC_ELAPSED, pname);
 }
     
 I2CDevice::~I2CDevice()
 {
     printf("I2C device bus %u address 0x%02x closed\n", 
            (unsigned)_busnum, (unsigned)_address);
+    perf_free(perf);
+    free(pname);
 }
 
 bool I2CDevice::transfer(const uint8_t *send, uint32_t send_len,
                          uint8_t *recv, uint32_t recv_len)
 {
-    return _px4dev.do_transfer(_address, send, send_len, recv, recv_len);
+    perf_begin(perf);
+    bool ret = _px4dev.do_transfer(_address, send, send_len, recv, recv_len);
+    perf_end(perf);
+    return ret;
 }
 
 bool I2CDevice::read_registers_multiple(uint8_t first_reg, uint8_t *recv,

libraries/AP_HAL_PX4/I2CDevice.h

@@ -72,6 +72,8 @@ private:
     uint8_t _busnum;
     PX4_I2C _px4dev;
     uint8_t _address;
+    perf_counter_t perf;
+    char *pname;
 };
 
 class I2CDeviceManager : public AP_HAL::I2CDeviceManager {