i2c: implement target mode for rp2040 and nrf

src/machine/machine_nrf528xx.go

@@ -9,19 +9,25 @@ import (
 
 // I2C on the NRF528xx.
 type I2C struct {
-	Bus *nrf.TWIM_Type
+	Bus  *nrf.TWIM_Type // Called Bus to align with Bus field in nrf51
+	BusT *nrf.TWIS_Type
+	mode I2CMode
 }
 
 // There are 2 I2C interfaces on the NRF.
 var (
-	I2C0 = &I2C{Bus: nrf.TWIM0}
-	I2C1 = &I2C{Bus: nrf.TWIM1}
+	I2C0 = &I2C{Bus: nrf.TWIM0, BusT: nrf.TWIS0}
+	I2C1 = &I2C{Bus: nrf.TWIM1, BusT: nrf.TWIS1}
 )
 
 func (i2c *I2C) enableAsController() {
 	i2c.Bus.ENABLE.Set(nrf.TWIM_ENABLE_ENABLE_Enabled)
 }
 
+func (i2c *I2C) enableAsTarget() {
+	i2c.BusT.ENABLE.Set(nrf.TWIS_ENABLE_ENABLE_Enabled)
+}
+
 func (i2c *I2C) disable() {
 	i2c.Bus.ENABLE.Set(0)
 }
@@ -86,6 +92,99 @@ func (i2c *I2C) Tx(addr uint16, w, r []byte) (err error) {
 	return
 }
 
+// Listen starts listening for I2C requests sent to specified address
+//
+// addr is the address to listen to
+func (i2c *I2C) Listen(addr uint8) error {
+	i2c.BusT.ADDRESS[0].Set(uint32(addr))
+	i2c.BusT.CONFIG.Set(nrf.TWIS_CONFIG_ADDRESS0_Enabled)
+
+	i2c.BusT.EVENTS_STOPPED.Set(0)
+	i2c.BusT.EVENTS_ERROR.Set(0)
+	i2c.BusT.EVENTS_RXSTARTED.Set(0)
+	i2c.BusT.EVENTS_TXSTARTED.Set(0)
+	i2c.BusT.EVENTS_WRITE.Set(0)
+	i2c.BusT.EVENTS_READ.Set(0)
+
+	return nil
+}
+
+// WaitForEvent blocks the current go-routine until an I2C event is received (when in Target mode).
+//
+// The passed buffer will be populated for receive events, with the number of bytes
+// received returned in count.  For other event types, buf is not modified and a count
+// of zero is returned.
+//
+// For request events, the caller MUST call `Reply` to avoid hanging the i2c bus indefinitely.
+func (i2c *I2C) WaitForEvent(buf []byte) (evt I2CTargetEvent, count int, err error) {
+	i2c.BusT.RXD.PTR.Set(uint32(uintptr(unsafe.Pointer(&buf[0]))))
+	i2c.BusT.RXD.MAXCNT.Set(uint32(len(buf)))
+
+	i2c.BusT.TASKS_PREPARERX.Set(nrf.TWIS_TASKS_PREPARERX_TASKS_PREPARERX_Trigger)
+
+	i2c.Bus.TASKS_RESUME.Set(1)
+
+	for i2c.BusT.EVENTS_STOPPED.Get() == 0 &&
+		i2c.BusT.EVENTS_READ.Get() == 0 {
+		gosched()
+
+		if i2c.BusT.EVENTS_ERROR.Get() != 0 {
+			i2c.BusT.EVENTS_ERROR.Set(0)
+			return I2CReceive, 0, twisError(i2c.BusT.ERRORSRC.Get())
+		}
+	}
+
+	count = 0
+	evt = I2CFinish
+	err = nil
+
+	if i2c.BusT.EVENTS_WRITE.Get() != 0 {
+		i2c.BusT.EVENTS_WRITE.Set(0)
+
+		// Data was sent to this target.  We've waited for
+		// READ or STOPPED event, so transmission should be
+		// complete.
+		count = int(i2c.BusT.RXD.AMOUNT.Get())
+		evt = I2CReceive
+	} else if i2c.BusT.EVENTS_READ.Get() != 0 {
+		i2c.BusT.EVENTS_READ.Set(0)
+
+		// Data is requested from this target, hw will stretch
+		// the controller's clock until there is a reply to
+		// send
+		evt = I2CRequest
+	} else if i2c.BusT.EVENTS_STOPPED.Get() != 0 {
+		i2c.BusT.EVENTS_STOPPED.Set(0)
+		evt = I2CFinish
+	}
+
+	return
+}
+
+// Reply supplies the response data the controller.
+func (i2c *I2C) Reply(buf []byte) error {
+	i2c.BusT.TXD.PTR.Set(uint32(uintptr(unsafe.Pointer(&buf[0]))))
+	i2c.BusT.TXD.MAXCNT.Set(uint32(len(buf)))
+
+	i2c.BusT.EVENTS_STOPPED.Set(0)
+
+	// Trigger Tx
+	i2c.BusT.TASKS_PREPARETX.Set(nrf.TWIS_TASKS_PREPARETX_TASKS_PREPARETX_Trigger)
+
+	// Block, waiting for Tx to complete
+	for i2c.BusT.EVENTS_STOPPED.Get() == 0 {
+		gosched()
+
+		if i2c.BusT.EVENTS_ERROR.Get() != 0 {
+			return twisError(i2c.BusT.ERRORSRC.Get())
+		}
+	}
+
+	i2c.BusT.EVENTS_STOPPED.Set(0)
+
+	return nil
+}
+
 // twiCError converts an I2C controller error to Go
 func twiCError(val uint32) error {
 	if val == 0 {
@@ -100,3 +199,18 @@ func twiCError(val uint32) error {
 
 	return errI2CBusError
 }
+
+// twisError converts an I2C target error to Go
+func twisError(val uint32) error {
+	if val == 0 {
+		return nil
+	} else if val&nrf.TWIS_ERRORSRC_OVERFLOW_Msk == nrf.TWIS_ERRORSRC_OVERFLOW {
+		return errI2COverflow
+	} else if val&nrf.TWIS_ERRORSRC_DNACK_Msk == nrf.TWIS_ERRORSRC_DNACK {
+		return errI2CAckExpected
+	} else if val&nrf.TWIS_ERRORSRC_OVERREAD_Msk == nrf.TWIS_ERRORSRC_OVERREAD {
+		return errI2COverread
+	}
+
+	return errI2CBusError
+}