s35770 driver fix, nullptr

src/drivers/rpm/s35770/s35770.cpp

@@ -66,26 +66,34 @@ int S35770::init()
 
 int S35770::probe()
 {
-
-	return PX4_OK;
+	uint32_t raw;
+	return getCounter(&raw);
 }
 
 
-uint32_t S35770::getCounter()
+uint8_t S35770::getCounter(uint32_t* count)
 {
-
 	uint8_t raw[3];
-	transfer(nullptr, 0, &raw[0], 3);
-	return uint32_t(hiWord(raw[0]) << 16 | loWord(raw[1]) << 8 | raw[2]);
+	uint8_t err = transfer(nullptr, 0, &raw[0], 3);
+	*count = uint32_t(hiWord(raw[0]) << 16 | loWord(raw[1]) << 8 | raw[2]);
+
+	return err;
 }
 
+
 void S35770::RunImpl()
 {
 	// read sensor and compute frequency
 	uint32_t oldcount = _count;
 	int32_t diffTime = hrt_elapsed_time(&_last_measurement_time);
 
-	_count = getCounter();
+	uint8_t err = getCounter(&_count);
+
+	if (err != PX4_OK) {
+		PX4_ERR("Error reading counter");
+		return;
+	}
+
 	_last_measurement_time = hrt_absolute_time();
 
 	uint32_t diffCount = 0;

src/drivers/rpm/s35770/s35770.hpp

@@ -68,13 +68,14 @@ class S35770 : public device::I2C, public ModuleParams, public I2CSPIDriver<S357
 
 private:
 
-	int  probe() override;
+	int  probe()	override;
 
-	uint32_t       getCounter();
+	uint8_t       getCounter(uint32_t* count);
 
 	uint8_t        hiWord(uint8_t in) { return (in & 0x0fu); }
 	uint8_t        loWord(uint8_t in) { return ((in & 0xf0u) >> 4); }
 
+
 	uint32_t       _count{0};
 	uint16_t       _overflow_count{0};
 	hrt_abstime    _last_measurement_time{0};