nrf: new peripheral type for nrf528xx chips

src/machine/machine_nrf5x.go

@@ -0,0 +1,101 @@
+//go:build nrf51 || nrf52
+
+package machine
+
+import "device/nrf"
+
+// I2C on the NRF51 and NRF52.
+type I2C struct {
+	Bus *nrf.TWI_Type
+}
+
+// There are 2 I2C interfaces on the NRF.
+var (
+	I2C0 = &I2C{Bus: nrf.TWI0}
+	I2C1 = &I2C{Bus: nrf.TWI1}
+)
+
+func (i2c *I2C) enableAsController() {
+	i2c.Bus.ENABLE.Set(nrf.TWI_ENABLE_ENABLE_Enabled)
+}
+
+func (i2c *I2C) disable() {
+	i2c.Bus.ENABLE.Set(0)
+}
+
+// Tx does a single I2C transaction at the specified address.
+// It clocks out the given address, writes the bytes in w, reads back len(r)
+// bytes and stores them in r, and generates a stop condition on the bus.
+func (i2c *I2C) Tx(addr uint16, w, r []byte) (err error) {
+
+	// Tricky stop condition.
+	// After reads, the stop condition is generated implicitly with a shortcut.
+	// After writes not followed by reads and in the case of errors, stop must be generated explicitly.
+
+	i2c.Bus.ADDRESS.Set(uint32(addr))
+
+	if len(w) != 0 {
+		i2c.Bus.TASKS_STARTTX.Set(1) // start transmission for writing
+		for _, b := range w {
+			if err = i2c.writeByte(b); err != nil {
+				i2c.signalStop()
+				return
+			}
+		}
+	}
+
+	if len(r) != 0 {
+		// To trigger suspend task when a byte is received
+		i2c.Bus.SHORTS.Set(nrf.TWI_SHORTS_BB_SUSPEND)
+		i2c.Bus.TASKS_STARTRX.Set(1) // re-start transmission for reading
+		for i := range r {           // read each char
+			if i+1 == len(r) {
+				// To trigger stop task when last byte is received, set before resume task.
+				i2c.Bus.SHORTS.Set(nrf.TWI_SHORTS_BB_STOP)
+			}
+			if i > 0 {
+				i2c.Bus.TASKS_RESUME.Set(1) // re-start transmission for reading
+			}
+			if r[i], err = i2c.readByte(); err != nil {
+				i2c.Bus.SHORTS.Set(nrf.TWI_SHORTS_BB_SUSPEND_Disabled)
+				i2c.signalStop()
+				return
+			}
+		}
+		i2c.Bus.SHORTS.Set(nrf.TWI_SHORTS_BB_SUSPEND_Disabled)
+	}
+
+	// Stop explicitly when no reads were executed, stoping unconditionally would be a mistake.
+	// It may execute after I2C peripheral has already been stopped by the shortcut in the read block,
+	// so stop task will trigger first thing in a subsequent transaction, hanging it.
+	if len(r) == 0 {
+		i2c.signalStop()
+	}
+
+	return
+}
+
+// writeByte writes a single byte to the I2C bus and waits for confirmation.
+func (i2c *I2C) writeByte(data byte) error {
+	i2c.Bus.TXD.Set(uint32(data))
+	for i2c.Bus.EVENTS_TXDSENT.Get() == 0 {
+		if e := i2c.Bus.EVENTS_ERROR.Get(); e != 0 {
+			i2c.Bus.EVENTS_ERROR.Set(0)
+			return errI2CBusError
+		}
+	}
+	i2c.Bus.EVENTS_TXDSENT.Set(0)
+	return nil
+}
+
+// readByte reads a single byte from the I2C bus when it is ready.
+func (i2c *I2C) readByte() (byte, error) {
+	for i2c.Bus.EVENTS_RXDREADY.Get() == 0 {
+		if e := i2c.Bus.EVENTS_ERROR.Get(); e != 0 {
+			i2c.Bus.EVENTS_ERROR.Set(0)
+			return 0, errI2CBusError
+		}
+	}
+	i2c.Bus.EVENTS_RXDREADY.Set(0)
+	return byte(i2c.Bus.RXD.Get()), nil
+}