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Optimize flash writes on SAMD51 #4908

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Merged
merged 1 commit into from
May 24, 2025
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Optimize flash writes on SAMD51 #4908

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17 changes: 7 additions & 10 deletions src/machine/machine_atsamd51.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2163,7 +2163,7 @@ func (f flashBlockDevice) ReadAt(p []byte, off int64) (n int, err error) {
}

// WriteAt writes the given number of bytes to the block device.
// Only word (32 bits) length data can be programmed.
// Data is written to the page buffer in 4-byte chunks, then saved to flash memory.
// See SAM-D5x-E5x-Family-Data-Sheet-DS60001507.pdf page 591-592.
// 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.
Expand All @@ -2185,16 +2185,13 @@ func (f flashBlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
waitWhileFlashBusy()

for j := 0; j < len(padded); j += int(f.WriteBlockSize()) {
// write first word using double-word low order word
*(*uint32)(unsafe.Pointer(address)) = binary.LittleEndian.Uint32(padded[j : j+int(f.WriteBlockSize()/2)])

// write second word using double-word high order word
*(*uint32)(unsafe.Add(unsafe.Pointer(address), uintptr(f.WriteBlockSize())/2)) = binary.LittleEndian.Uint32(padded[j+int(f.WriteBlockSize()/2) : j+int(f.WriteBlockSize())])

waitWhileFlashBusy()
// page buffer is 512 bytes long, but only 4 bytes can be written at once
for k := 0; k < int(f.WriteBlockSize()); k += 4 {
*(*uint32)(unsafe.Pointer(address + uintptr(k))) = binary.LittleEndian.Uint32(padded[j+k : j+k+4])
}

sam.NVMCTRL.SetADDR(uint32(address))
sam.NVMCTRL.CTRLB.Set(sam.NVMCTRL_CTRLB_CMD_WQW | (sam.NVMCTRL_CTRLB_CMDEX_KEY << sam.NVMCTRL_CTRLB_CMDEX_Pos))
sam.NVMCTRL.CTRLB.Set(sam.NVMCTRL_CTRLB_CMD_WP | (sam.NVMCTRL_CTRLB_CMDEX_KEY << sam.NVMCTRL_CTRLB_CMDEX_Pos))

waitWhileFlashBusy()

Expand All @@ -2213,7 +2210,7 @@ func (f flashBlockDevice) Size() int64 {
return int64(FlashDataEnd() - FlashDataStart())
}

const writeBlockSize = 8
const writeBlockSize = 512

// WriteBlockSize returns the block size in which data can be written to
// memory. It can be used by a client to optimize writes, non-aligned writes
Expand Down