machine: remove bytes package dependency in flash code

This also moves flash padding code to a single place, since it was
copied 5 times.

This change is necessary in Go 1.24 to avoid an import cycle.

src/machine/flash.go

@@ -64,3 +64,14 @@ type BlockDevice interface {
 	// EraseBlockSize to map addresses to blocks.
 	EraseBlocks(start, len int64) error
 }
+
+// pad data if needed so it is long enough for correct byte alignment on writes.
+func flashPad(p []byte, writeBlockSize int) []byte {
+	overflow := len(p) % writeBlockSize
+	if overflow != 0 {
+		for i := 0; i < writeBlockSize-overflow; i++ {
+			p = append(p, 0xff)
+		}
+	}
+	return p
+}

src/machine/machine_atsamd21.go

@@ -7,7 +7,6 @@
 package machine
 
 import (
-	"bytes"
 	"device/arm"
 	"device/sam"
 	"errors"
@@ -1917,7 +1916,7 @@ func (f flashBlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
 	f.ensureInitComplete()
 
 	address := FlashDataStart() + uintptr(off)
-	padded := f.pad(p)
+	padded := flashPad(p, int(f.WriteBlockSize()))
 
 	waitWhileFlashBusy()
 
@@ -1992,17 +1991,6 @@ func (f flashBlockDevice) EraseBlocks(start, len int64) error {
 	return nil
 }
 
-// pad data if needed so it is long enough for correct byte alignment on writes.
-func (f flashBlockDevice) pad(p []byte) []byte {
-	overflow := int64(len(p)) % f.WriteBlockSize()
-	if overflow == 0 {
-		return p
-	}
-
-	padding := bytes.Repeat([]byte{0xff}, int(f.WriteBlockSize()-overflow))
-	return append(p, padding...)
-}
-
 func (f flashBlockDevice) ensureInitComplete() {
 	if f.initComplete {
 		return

src/machine/machine_atsamd51.go

@@ -7,7 +7,6 @@
 package machine
 
 import (
-	"bytes"
 	"device/arm"
 	"device/sam"
 	"errors"
@@ -2174,7 +2173,7 @@ func (f flashBlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
 	}
 
 	address := FlashDataStart() + uintptr(off)
-	padded := f.pad(p)
+	padded := flashPad(p, int(f.WriteBlockSize()))
 
 	settings := disableFlashCache()
 	defer restoreFlashCache(settings)
@@ -2263,17 +2262,6 @@ func (f flashBlockDevice) EraseBlocks(start, len int64) error {
 	return nil
 }
 
-// pad data if needed so it is long enough for correct byte alignment on writes.
-func (f flashBlockDevice) pad(p []byte) []byte {
-	overflow := int64(len(p)) % f.WriteBlockSize()
-	if overflow == 0 {
-		return p
-	}
-
-	padding := bytes.Repeat([]byte{0xff}, int(f.WriteBlockSize()-overflow))
-	return append(p, padding...)
-}
-
 func disableFlashCache() uint16 {
 	settings := sam.NVMCTRL.CTRLA.Get()
 

src/machine/machine_nrf.go

@@ -3,7 +3,6 @@
 package machine
 
 import (
-	"bytes"
 	"device/nrf"
 	"internal/binary"
 	"runtime/interrupt"
@@ -386,7 +385,7 @@ func (f flashBlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
 	}
 
 	address := FlashDataStart() + uintptr(off)
-	padded := f.pad(p)
+	padded := flashPad(p, int(f.WriteBlockSize()))
 
 	waitWhileFlashBusy()
 
@@ -444,17 +443,6 @@ func (f flashBlockDevice) EraseBlocks(start, len int64) error {
 	return nil
 }
 
-// pad data if needed so it is long enough for correct byte alignment on writes.
-func (f flashBlockDevice) pad(p []byte) []byte {
-	overflow := int64(len(p)) % f.WriteBlockSize()
-	if overflow == 0 {
-		return p
-	}
-
-	padding := bytes.Repeat([]byte{0xff}, int(f.WriteBlockSize()-overflow))
-	return append(p, padding...)
-}
-
 func waitWhileFlashBusy() {
 	for nrf.NVMC.GetREADY() != nrf.NVMC_READY_READY_Ready {
 	}

src/machine/machine_rp2040_flash.go

@@ -3,7 +3,6 @@
 package machine
 
 import (
-	"bytes"
 	"unsafe"
 )
 
@@ -101,17 +100,6 @@ func (f flashBlockDevice) EraseBlocks(start, length int64) error {
 	return f.eraseBlocks(start, length)
 }
 
-// pad data if needed so it is long enough for correct byte alignment on writes.
-func (f flashBlockDevice) pad(p []byte) []byte {
-	overflow := int64(len(p)) % f.WriteBlockSize()
-	if overflow == 0 {
-		return p
-	}
-
-	padding := bytes.Repeat([]byte{0xff}, int(f.WriteBlockSize()-overflow))
-	return append(p, padding...)
-}
-
 // return the correct address to be used for write
 func writeAddress(off int64) uintptr {
 	return readAddress(off) - uintptr(memoryStart)

src/machine/machine_rp2040_rom.go

@@ -230,7 +230,7 @@ func (f flashBlockDevice) writeAt(p []byte, off int64) (n int, err error) {
 	// e.g. real address 0x10003000 is written to at
 	// 0x00003000
 	address := writeAddress(off)
-	padded := f.pad(p)
+	padded := flashPad(p, int(f.WriteBlockSize()))
 
 	C.flash_range_write(C.uint32_t(address),
 		(*C.uint8_t)(unsafe.Pointer(&padded[0])),

src/machine/machine_stm32_flash.go

@@ -5,7 +5,6 @@ package machine
 import (
 	"device/stm32"
 
-	"bytes"
 	"unsafe"
 )
 
@@ -41,7 +40,8 @@ func (f flashBlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
 	unlockFlash()
 	defer lockFlash()
 
-	return writeFlashData(FlashDataStart()+uintptr(off), f.pad(p))
+	p = flashPad(p, int(f.WriteBlockSize()))
+	return writeFlashData(FlashDataStart()+uintptr(off), p)
 }
 
 // Size returns the number of bytes in this block device.
@@ -90,17 +90,6 @@ func (f flashBlockDevice) EraseBlocks(start, len int64) error {
 	return nil
 }
 
-// pad data if needed so it is long enough for correct byte alignment on writes.
-func (f flashBlockDevice) pad(p []byte) []byte {
-	overflow := int64(len(p)) % f.WriteBlockSize()
-	if overflow == 0 {
-		return p
-	}
-
-	padding := bytes.Repeat([]byte{0xff}, int(f.WriteBlockSize()-overflow))
-	return append(p, padding...)
-}
-
 const memoryStart = 0x08000000
 
 func unlockFlash() {