nrf: new peripheral type for nrf528xx chips

src/machine/machine_nrf528xx.go

@@ -0,0 +1,102 @@
+//go:build nrf52840 || nrf52833
+
+package machine
+
+import (
+	"device/nrf"
+	"unsafe"
+)
+
+// I2C on the NRF528xx.
+type I2C struct {
+	Bus *nrf.TWIM_Type
+}
+
+// There are 2 I2C interfaces on the NRF.
+var (
+	I2C0 = &I2C{Bus: nrf.TWIM0}
+	I2C1 = &I2C{Bus: nrf.TWIM1}
+)
+
+func (i2c *I2C) enableAsController() {
+	i2c.Bus.ENABLE.Set(nrf.TWIM_ENABLE_ENABLE_Enabled)
+}
+
+func (i2c *I2C) disable() {
+	i2c.Bus.ENABLE.Set(0)
+}
+
+// Tx does a single I2C transaction at the specified address (when in controller mode).
+//
+// 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) {
+	i2c.Bus.ADDRESS.Set(uint32(addr))
+
+	i2c.Bus.EVENTS_STOPPED.Set(0)
+	i2c.Bus.EVENTS_ERROR.Set(0)
+	i2c.Bus.EVENTS_RXSTARTED.Set(0)
+	i2c.Bus.EVENTS_TXSTARTED.Set(0)
+	i2c.Bus.EVENTS_LASTRX.Set(0)
+	i2c.Bus.EVENTS_LASTTX.Set(0)
+	i2c.Bus.EVENTS_SUSPENDED.Set(0)
+
+	// Configure for a single shot to perform both write and read (as applicable)
+	if len(w) != 0 {
+		i2c.Bus.TXD.PTR.Set(uint32(uintptr(unsafe.Pointer(&w[0]))))
+		i2c.Bus.TXD.MAXCNT.Set(uint32(len(w)))
+
+		// If no read, immediately signal stop after TX
+		if len(r) == 0 {
+			i2c.Bus.SHORTS.Set(nrf.TWIM_SHORTS_LASTTX_STOP)
+		}
+	}
+	if len(r) != 0 {
+		i2c.Bus.RXD.PTR.Set(uint32(uintptr(unsafe.Pointer(&r[0]))))
+		i2c.Bus.RXD.MAXCNT.Set(uint32(len(r)))
+
+		// Auto-start Rx after Tx and Stop after Rx
+		i2c.Bus.SHORTS.Set(nrf.TWIM_SHORTS_LASTTX_STARTRX | nrf.TWIM_SHORTS_LASTRX_STOP)
+	}
+
+	// Fire the transaction
+	i2c.Bus.TASKS_RESUME.Set(1)
+	if len(w) != 0 {
+		i2c.Bus.TASKS_STARTTX.Set(1)
+	} else if len(r) != 0 {
+		i2c.Bus.TASKS_STARTRX.Set(1)
+	}
+
+	// Wait until transaction stopped to ensure buffers fully processed
+	for i2c.Bus.EVENTS_STOPPED.Get() == 0 {
+		// Allow scheduler to run
+		gosched()
+
+		// Handle errors by ensuring STOP sent on bus
+		if i2c.Bus.EVENTS_ERROR.Get() != 0 {
+			if i2c.Bus.EVENTS_STOPPED.Get() == 0 {
+				// STOP cannot be sent during SUSPEND
+				i2c.Bus.TASKS_RESUME.Set(1)
+				i2c.Bus.TASKS_STOP.Set(1)
+			}
+			err = twiCError(i2c.Bus.ERRORSRC.Get())
+		}
+	}
+
+	return
+}
+
+// twiCError converts an I2C controller error to Go
+func twiCError(val uint32) error {
+	if val == 0 {
+		return nil
+	} else if val&nrf.TWIM_ERRORSRC_OVERRUN_Msk == nrf.TWIM_ERRORSRC_OVERRUN {
+		return errI2CBusError
+	} else if val&nrf.TWIM_ERRORSRC_ANACK_Msk == nrf.TWIM_ERRORSRC_ANACK {
+		return errI2CAckExpected
+	} else if val&nrf.TWIM_ERRORSRC_DNACK_Msk == nrf.TWIM_ERRORSRC_DNACK {
+		return errI2CAckExpected
+	}
+
+	return errI2CBusError
+}