nrf: support flash operations while the SoftDevice is enabled

Flash operations must go through the SoftDevice if it is enabled,
otherwise they will crash the chip. (And even then the SoftDevice
doesn't guarantee they'll succeed, depending on advertisement frequency
etc). But this patch makes sure to call the appropriate APIs so that
flash is usable while using Bluetooth.

src/machine/machine_nrf.go

@@ -3,7 +3,9 @@
 package machine
 
 import (
+	"device/arm"
 	"device/nrf"
+	"errors"
 	"internal/binary"
 	"runtime/interrupt"
 	"unsafe"
@@ -380,6 +382,10 @@ func (f flashBlockDevice) ReadAt(p []byte, off int64) (n int, err error) {
 // If the length of p is not long enough it will be padded with 0xFF bytes.
 // This method assumes that the destination is already erased.
 func (f flashBlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
+	if len(p) == 0 {
+		return 0, nil // nothing to do (and it would fail in sd_flash_write)
+	}
+
 	if FlashDataStart()+uintptr(off)+uintptr(len(p)) > FlashDataEnd() {
 		return 0, errFlashCannotWritePastEOF
 	}
@@ -387,6 +393,34 @@ func (f flashBlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
 	address := FlashDataStart() + uintptr(off)
 	padded := flashPad(p, int(f.WriteBlockSize()))
 
+	// When the SoftDevice is enabled, access to the flash is restricted and
+	// must go through the SoftDevice API.
+	if isSoftDeviceEnabled() {
+		// Call sd_flash_write, which is SVC_SOC_BASE + 9 in all the
+		// SoftDevices I've checked.
+		// Documentation:
+		// https://docs.nordicsemi.com/bundle/s140_v6.0.0_api/page/group_n_r_f_s_o_c_f_u_n_c_t_i_o_n_s.html
+		result := arm.SVCall3(0x20+9, address, &p[0], uint32(len(p)))
+		if result != 0 {
+			// Could not queue flash operation? Not sure when this can
+			// happen.
+			return 0, flashError
+		}
+
+		// Wait until the SoftDevice is finished.
+		flashStatus = flashStatusBusy
+		for flashStatus == flashStatusBusy {
+			handleSoftDeviceEvents()
+		}
+
+		// Check whether the operation was successful.
+		if flashStatus != flashStatusOk {
+			flashStatus = flashStatusOk
+			return 0, flashError
+		}
+		return len(p), nil
+	}
+
 	waitWhileFlashBusy()
 
 	nrf.NVMC.SetCONFIG_WEN(nrf.NVMC_CONFIG_WEN_Wen)
@@ -428,6 +462,40 @@ func (f flashBlockDevice) EraseBlockSize() int64 {
 // supports this. The start and len parameters are in block numbers, use
 // EraseBlockSize to map addresses to blocks.
 func (f flashBlockDevice) EraseBlocks(start, len int64) error {
+	// When the SoftDevice is enabled, access to the flash is restricted and
+	// must go through the SoftDevice API.
+	if isSoftDeviceEnabled() {
+		for i := range uint32(len) {
+			flashPage := uint32(FlashDataStart())/eraseBlockSizeValue + uint32(start) + i
+
+			// Call sd_flash_page_erase, which is SVC_SOC_BASE + 8 in all the
+			// SoftDevices I've checked.
+			// Documentation:
+			// https://docs.nordicsemi.com/bundle/s140_v6.0.0_api/page/group_n_r_f_s_o_c_f_u_n_c_t_i_o_n_s.html#ga9c93dd94a138ad8b5ed3693ea38ffb3e
+			result := arm.SVCall1(0x20+8, flashPage)
+			if result != 0 {
+				// Could not queue flash operation? Not sure when this can
+				// happen.
+				return flashError
+			}
+
+			// Wait until the SoftDevice is finished.
+			flashStatus = flashStatusBusy
+			for flashStatus == flashStatusBusy {
+				handleSoftDeviceEvents()
+			}
+
+			// Check whether the operation was successful.
+			if flashStatus != flashStatusOk {
+				flashStatus = flashStatusOk
+				return flashError
+			}
+		}
+		return nil
+	}
+
+	// SoftDevice is not used or enabled. Use NVIC directly.
+
 	address := FlashDataStart() + uintptr(start*f.EraseBlockSize())
 	waitWhileFlashBusy()
 
@@ -447,3 +515,52 @@ func waitWhileFlashBusy() {
 	for nrf.NVMC.GetREADY() != nrf.NVMC_READY_READY_Ready {
 	}
 }
+
+var flashError = errors.New("machine: flash operation failed")
+
+const (
+	flashStatusOk = iota
+	flashStatusError
+	flashStatusBusy
+)
+
+var flashStatus uint8 = flashStatusOk
+
+var sdEvent uint32
+
+// Process all queued SoftDevice events. May only be called when the SoftDevice is enabled.
+//
+// Normally these are handled in the same interrupt where Bluetooth events are
+// handled. But in TinyGo, that's complicated. One option would be to put it in
+// the tinygo.org/x/bluetooth package, but that would cause a circular
+// dependency between the machine and the bluetooth package. Another would be to
+// put it here, but let the bluetooth package call handleSoftDeviceEvents, but
+// that relies on updating the bluetooth package at the same time. As a
+// compromise, these events are handled directly where they are expected (here
+// in the machine package). This works in practice since there are only very few
+// of such events (at the moment, only flash-related ones which is in the
+// machine package anyway).
+func handleSoftDeviceEvents() {
+	for {
+		var result uintptr
+		if nrf.Device == "nrf52" || nrf.Device == "nrf52840" || nrf.Device == "nrf52833" {
+			// sd_evt_get: SOC_SVC_BASE_NOT_AVAILABLE + 31
+			result = arm.SVCall1(0x2C+31, &sdEvent)
+		} else {
+			return // TODO: nrf51 etc
+		}
+		if result != 0 {
+			// Some error occured. The only possible error is
+			// NRF_ERROR_NOT_FOUND, which means there are no more events.
+			return
+		}
+
+		// The following events are the same numbers in all SoftDevices I've checked.
+		switch sdEvent {
+		case 2: // NRF_EVT_FLASH_OPERATION_SUCCESS
+			flashStatus = flashStatusOk
+		case 3: // NRF_EVT_FLASH_OPERATION_ERROR
+			flashStatus = flashStatusError
+		}
+	}
+}