Add support for CEVA BNO08x 9DoF sensor (#809)

* Add support for CEVA BNO08x 9DoF sensor. Also includes implementation of CEVA SH-2 and SHTP protocols.

* Replace machine.I2C with drivers.I2C interface to remove dependency on machine package

* Replace Pin functionality with that provided by tinygo.org/x/drivers/internal/pin

* Unexport fields on SensorValue and replace with accessor methods. Add check for correct SensorID validation

* Add example to smoketest.sh

* Change build target for smoketest to match development environment.. Probably not important, but matches reality.

* Fix decoding of some sensor data: Step Counter, Tap Detector, Flip Detector. These are experimental.

* Refactor to allow SPI/UART etc. SPI is currently under development, but is omitted from this commit.

Example code has been moved to i2c subdirectory.

This commit introduces some major refactoring changes. It introduces a "Buser" interface and tries to remove any I2C specific code from the core. It still retains a couple of I2C specific fields in the "Config" struct ("Address" and "ReadChunk") but they are ignored in the as yet uncommited SPI code.

* Fix CRLF -> LF for gofmt

* Update smoketest to point to new example file

bno08x/shtp.go

@@ -0,0 +1,83 @@
+// SHTP specification found at https://www.ceva-ip.com/wp-content/uploads/SH-2-SHTP-Reference-Manual.pdf
+
+package bno08x
+
+import "encoding/binary"
+
+// shtpHandler is a callback for handling SHTP channel data.
+type shtpHandler func(payload []byte, timestamp uint32)
+
+// shtp implements the Sensor Hub Transport Protocol layer.
+type shtp struct {
+	hal      *hal
+	handlers map[uint8]shtpHandler
+	seq      [8]uint8
+	rx       [maxTransferIn]byte  // Reusable receive buffer
+	tx       [maxTransferOut]byte // Reusable transmit buffer
+}
+
+func newSHTP(hal *hal) *shtp {
+	return &shtp{
+		hal:      hal,
+		handlers: make(map[uint8]shtpHandler),
+	}
+}
+
+// register registers a handler for a specific SHTP channel.
+func (s *shtp) register(channel uint8, handler shtpHandler) {
+	if handler == nil {
+		delete(s.handlers, channel)
+		return
+	}
+	s.handlers[channel] = handler
+}
+
+// send transmits a payload on the specified channel.
+func (s *shtp) send(channel uint8, payload []byte) error {
+	total := len(payload) + shtpHeaderLength
+	if total > maxTransferOut {
+		return errFrameTooLarge
+	}
+
+	// Use pre-allocated transmit buffer to avoid allocations
+	frame := s.tx[:total]
+	binary.LittleEndian.PutUint16(frame[0:2], uint16(total))
+	frame[2] = channel
+	frame[3] = s.seq[channel]
+	s.seq[channel]++
+	copy(frame[shtpHeaderLength:], payload)
+
+	_, err := s.hal.write(frame)
+	return err
+}
+
+// poll checks for and processes incoming SHTP packets.
+// Returns true if a packet was processed, false if no data available.
+func (s *shtp) poll() (bool, error) {
+	n, timestamp, err := s.hal.read(s.rx[:])
+	if err != nil {
+		return false, err
+	}
+	if n == 0 {
+		return false, nil
+	}
+
+	packet := s.rx[:n]
+	length := int(binary.LittleEndian.Uint16(packet[0:2]) & ^uint16(continueMask))
+	if length > n {
+		length = n
+	}
+	if length < shtpHeaderLength {
+		return false, nil
+	}
+
+	channel := packet[2]
+	// seq := packet[3] // sequence number, not currently validated
+	payload := packet[shtpHeaderLength:length]
+
+	if handler := s.handlers[channel]; handler != nil {
+		handler(payload, timestamp)
+	}
+
+	return true, nil
+}