[RP2] Flash functions hang the board with a 16MiB flash

[digitalentity]

I have a custom board based on the RP2350 with a W25Q128JV (16 MiB) instead of W25Q32JV (4 MiB). The board boots and works fine as long as I don't use the machine.EraseBlocks() or other flash-related functions. If I do - the board hangs immediately.

[digitalentity]

I suspect this might be related to the #5408. I'll try to debug this a bit.

[digitalentity]

Minimal repro:

func main() {
    _ = machine.DeviceID()
}

[Gustavomurta]

machine.EraseBlocks?
Which blocks do you intend to erase?
The flash memory contains your program.

[digitalentity]

machine.EraseBlocks?

The 128K block at the end of the 1M. The linker script guarantees that there is no program there. Also, the same code works fine on 2M and 4M flash boards. Something is special about the way the runtime (or the bootrom) handles the 16M chip.

[Gustavomurta]

References about Flash memory in the RP2350 Board:

Hardware desygn with RP2350:
https://pip-assets.raspberrypi.com/categories/1214-rp2350/documents/RP-008280-DS-1-hardware-design-with-rp2350.pdf?disposition=inline

Chapter 3. Flash Memory

In order to be able to store program code which RP2350 can boot and run from, we need to use a flash memory, specifically, a quad SPI flash memory. The device chosen here is an W25Q128JVS device (U3 in the Figure 8), which is a 128Mbit chip (16MB). This is the largest memory size that RP2350 can support.

Did you assemble the custom board you're using yourself?

RP2350 Datasheet:
https://pip-assets.raspberrypi.com/categories/1214-rp2350/documents/RP-008373-DS-2-rp2350-datasheet.pdf?disposition=inline#section_qmi

2.2. Address map

2.2.2. XIP

12.14. QSPI memory interface (QMI)

rp2350 - flash 16MIB - Which area can I erase and how?
https://chatgpt.com/c/6a130390-06b8-83e9-aa6f-d826783d3e6c
< Assess whether this information is accurate.>

On the RP2350, the external QSPI flash is memory-mapped starting at:

0x10000000

If you have a 16 MiB flash:

Flash range:
0x10000000 .. 0x10FFFFFF

However, you cannot safely erase the area where your program is currently executing (XIP = Execute In Place), because the CPU fetches instructions directly from flash.

Safe recommendation for 16 MiB flash

Reserve:

Region Size
Firmware 0–2 MiB
Config/data/logs 2–16 MiB

Then erase/write only above:

FLASH_TARGET_OFFSET >= 0x200000

[digitalentity]

Did you assemble the custom board you're using yourself?

Yes, although I don't see how this is related here, especially given the following:

• The Pico SDK code works with the W25Q128JVS board without without issue including erasing and writing flash.
• The TinyGo code also boots and works fine with this board as long as I don't try to erase or write the flash memory.

However, you cannot safely erase the area where your program is currently executing (XIP = Execute In Place), because the CPU fetches instructions directly from flash.

The Pico SDK (and TinyGo machine package as well) moves code that interfaces with flash into RAM, so XIP can be safely disabled and re-enabled afterwards.

Safe recommendation for 16 MiB flash

Too bad that even using the last 4K page of the 16M area still hangs the CPU.

On a side note - I could have asked ChatGPT myself, you know. I'm writing here only because there is an apparent bug in either the compiler or runtime.

[Gustavomurta]

I didn't mean to offend you. I used Chatgpt to make it easier for me to understand.

[Gustavomurta]

My intention is to help you, even though I'm not an experienced programmer, but I am a hardware expert.
Could you please let us know if you have already performed this test with your board?

https://github.com/tinygo-org/tinygo/blob/dev/src/examples/flash/main.go

[Gustavomurta]

Testing my original Raspberry Pico 2 board:
MCU: RP2350 A0A2
Flash: W25Q32 RVXHJQ (4MiB)

/*
Raspberry Pico 2 - RP2350 - Flash test
https://github.com/tinygo-org/tinygo/blob/dev/src/examples/flash/main.go
Gustavo Murta 2026_05_24
tinygo version 0.39.0 windows/amd64 (using go version go1.25.1 and LLVM version 19.1.2)
C:\Users\jgust\tinygo\programas\Raspberry_Pico2\Flash_memory
tinygo flash -target pico2 main.go
*/

---- Opened the serial port COM7 ----
Flash data start:       0x10003000
Flash data end:         0x10400000
Flash data size, bytes: 4182016
Flash write block size: 256
Flash erase block size: 4096

Reading original data from flash:
1234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321
Erasing flash...
Writing new data to flash:
1234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321
Reading data back from flash: 
1234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321123456788765432112345678876543211234567887654321
Done.

[Gustavomurta]

Testing my RP2350B We Act board:
https://github.com/WeActStudio/WeActStudio.RP2350BCoreBoard
MCU = RP2350 B04A
Flash = W25Q128JVS (16MiB)

/*
Raspberry Pico 2 - RP2350 - Flash test
https://github.com/tinygo-org/tinygo/blob/dev/src/examples/flash/main.go
Gustavo Murta 2026_05_24
tinygo version 0.39.0 windows/amd64 (using go version go1.25.1 and LLVM version 19.1.2)
C:\Users\jgust\tinygo\programas\Raspberry_Pico2\Flash_memory
tinygo flash -target pico2 main.go
*/

MCU crashes!

---- Closed the serial port COM7 ----
---- Opened the serial port COM7 ----
Flash dat

[Gustavomurta]

Testing my RP2350B We Act board:

Reading only the data. Other functions were disregarded.
Notice that the Flash data start value is different and the Flash data size is incorrect.
Reading the data has corrupted data.

---- Opened the serial port COM7 ----
Flash data start:       0x10004000
Flash data end:         0x10400000
Flash data size, bytes: 4177920
Flash write block size: 256
Flash erase block size: 4096

Reading original data from flash:
     E/F  
          EgڵBj  
O P      Ed      I  Q 0   Ah  
                                 #}
   5       
               
                    [  1
   2      aF   (L OF     

   h B0 0 B-Ҙ   GF `EFFW 
                                  P  
                                       P  22 lE  H H    FUE         Y -  O  
Done.

/*
Raspberry Pico 2 - RP2350 - Flash test V2
https://github.com/tinygo-org/tinygo/blob/dev/src/examples/flash/main.go
Gustavo Murta 2026_05_24
tinygo version 0.39.0 windows/amd64 (using go version go1.25.1 and LLVM version 19.1.2)
C:\Users\jgust\tinygo\programas\Raspberry_Pico2\Flash_memory
tinygo flash -target pico2 main.go
*/

package main

import (
	"machine"
	"time"
)

var (
	err     error
	message = "1234567887654321123456788765432112345678876543211234567887654321" +
		"1234567887654321123456788765432112345678876543211234567887654321" +
		"1234567887654321123456788765432112345678876543211234567887654321" +
		"1234567887654321123456788765432112345678876543211234567887654321"
)

func main() {
	time.Sleep(3 * time.Second)

	// Print out general information
	println("Flash data start:      ", machine.FlashDataStart())
	println("Flash data end:        ", machine.FlashDataEnd())
	println("Flash data size, bytes:", machine.Flash.Size())
	println("Flash write block size:", machine.Flash.WriteBlockSize())
	println("Flash erase block size:", machine.Flash.EraseBlockSize())
	println()

	original := make([]byte, len(message))
	//saved := make([]byte, len(message))

	// Read flash contents on start (data shall survive power off)
	println("Reading original data from flash:")
	_, err = machine.Flash.ReadAt(original, 0)
	checkError(err)
	println(string(original))

	/*
			// erase flash
			println("Erasing flash...")
			needed := int64(len(message)) / machine.Flash.EraseBlockSize()
			if needed == 0 {
				// have to erase at least 1 block
				needed = 1
			}

			err := machine.Flash.EraseBlocks(0, needed)
			checkError(err)



		// Write the message to flash
		println("Writing new data to flash:")
		_, err = machine.Flash.WriteAt([]byte(message), 0)
		checkError(err)
		println(string(message))

		// Read back flash contents after write (verify data is the same as written)
		println("Reading data back from flash: ")
		_, err = machine.Flash.ReadAt(saved, 0)
		checkError(err)
		if !equal(saved, []byte(message)) {
			println("data verify error")
		}

		println(string(saved))

	*/
	println("Done.")
}

func equal(a, b []byte) bool {
	if len(a) != len(b) {
		return false
	}
	for i, v := range a {
		if v != b[i] {
			return false
		}
	}
	return true
}

func checkError(err error) {
	if err != nil {
		for {
			println(err.Error())
			time.Sleep(time.Second)
		}
	}
}

[Gustavomurta]

Analyzing the first symptom:

Original Pico2 = Flash data start: 0x10003000
RP2350B We Act Board = Flash data start: 0x10004000

Reference:
https://github.com/tinygo-org/tinygo/blob/dev/src/machine/machine_rp2_flash.go

// return the correct address to be used for reads
func readAddress(off int64) uintptr {
	return **FlashDataStart()** + uintptr(off)
}

https://github.com/tinygo-org/tinygo/blob/dev/src/machine/flash.go

// Return the start of the writable flash area, aligned on a page boundary. This
// is usually just after the program and static data.
func FlashDataStart() uintptr {
	pagesize := uintptr(eraseBlockSize())
	return (uintptr(unsafe.Pointer(&flashDataStart)) + pagesize - 1) &^ (pagesize - 1)
}

https://github.com/tinygo-org/tinygo/blob/dev/src/machine/machine_rp2350_rom.go

#define XIP_BASE     0x10000000
#define XIP_QMI_BASE 0x400d0000
#define IO_QSPI_BASE 0x40030000
#define BOOTRAM_BASE 0x400e0000

// Flash related code
const memoryStart = C.XIP_BASE // memory start for purpose of erase

func (f flashBlockDevice) writeAt(p []byte, off int64) (n int, err error) {
	if writeAddress(off)+uintptr(C.XIP_BASE) > FlashDataEnd() {
		return 0, errFlashCannotWritePastEOF
	}

	state := interrupt.Disable()
	defer interrupt.Restore(state)

	// rp2350 writes to offset, not actual address
	// e.g. real address 0x10003000 is written to at
	// 0x00003000
	address := writeAddress(off)
	padded := flashPad(p, int(f.WriteBlockSize()))

	C.flash_range_write(C.uint32_t(address),
		(*C.uint8_t)(unsafe.Pointer(&padded[0])),
		C.ulong(len(padded)))

	return len(padded), nil
}


func (f flashBlockDevice) eraseBlocks(start, length int64) error {
	address := writeAddress(start * f.EraseBlockSize())
	if address+uintptr(C.XIP_BASE) > FlashDataEnd() {
		return errFlashCannotErasePastEOF
	}

	state := interrupt.Disable()
	defer interrupt.Restore(state)

	C.flash_erase_blocks(C.uint32_t(address), C.ulong(length*f.EraseBlockSize()))

	return nil
}

[Gustavomurta]

Testing my RP2350B We Act board:

4182016 (0x3fd000) Bytes : Flash Data size

---- Reopened serial port COM7 ----
Flash data start: 0x10003000
Flash data end  : 0x10400000
Available: 0x003fd000

package main

import (
	"machine"
	"time"
)

func main() {

	start := machine.FlashDataStart()
	end := machine.FlashDataEnd()

	time.Sleep(3 * time.Second)
	println("Flash data start:", start)
	println("Flash data end  :", end)

	size := end - start

	println("Available:", size)

	for {
	}
}

[Gustavomurta]

Testing my RP2350B We Act board:

Reducing the message size. An error was readed. Garbage?
Flash data start is the same as the Original Pico2.

---- Opened the serial port COM7 ----
Flash data start:       0x10003000
Flash data end:         0x10400000
Flash data size, bytes: 4182016
Flash write block size: 256
Flash erase block size: 4096

Reading original data from flash:
��� �heap alloc in interruptout o
Done.

/*
Raspberry Pico 2 - RP2350 - Flash test V2
https://github.com/tinygo-org/tinygo/blob/dev/src/examples/flash/main.go
Gustavo Murta 2026_05_24
tinygo version 0.39.0 windows/amd64 (using go version go1.25.1 and LLVM version 19.1.2)
C:\Users\jgust\tinygo\programas\Raspberry_Pico2\Flash_memory
tinygo flash -target pico2 main.go
*/

package main

import (
	"machine"
	"time"
)

var (
	err     error
	message = "1234567887654321123456788765432112345678876543211234567887654321"	
)

func main() {
	time.Sleep(3 * time.Second)

	// Print out general information
	println("Flash data start:      ", machine.FlashDataStart())
	println("Flash data end:        ", machine.FlashDataEnd())
	println("Flash data size, bytes:", machine.Flash.Size())
	println("Flash write block size:", machine.Flash.WriteBlockSize())
	println("Flash erase block size:", machine.Flash.EraseBlockSize())
	println()

	original := make([]byte, len(message))
	//saved := make([]byte, len(message))

	// Read flash contents on start (data shall survive power off)
	println("Reading original data from flash:")
	_, err = machine.Flash.ReadAt(original, 0)
	checkError(err)
	println(string(original))

	println("Done.")
}

func checkError(err error) {
	if err != nil {
		for {
			println(err.Error())
			time.Sleep(time.Second)
		}
	}
}

[Gustavomurta]

Analyzing Tinygo code:
Some Tinygo Flash memory functions are derived from C programming functions.
Programming for use with flash memory is not simple.
I will continue the research later.

https://github.com/tinygo-org/tinygo/blob/dev/src/machine/machine_rp2350_rom.go

Raspberry Pico C++ SDK:
https://github.com/raspberrypi/pico-sdk/tree/master/src/rp2_common/hardware_flash
https://github.com/raspberrypi/pico-sdk/blob/master/src/boards/include/boards/weact_studio_rp2350b_core.h

// --- FLASH ---
#define PICO_BOOT_STAGE2_CHOOSE_W25Q080 1

#ifndef PICO_FLASH_SPI_CLKDIV
#define PICO_FLASH_SPI_CLKDIV 2
#endif

pico_board_cmake_set_default(PICO_FLASH_SIZE_BYTES, (16 * 1024 * 1024))
#ifndef PICO_FLASH_SIZE_BYTES
#define PICO_FLASH_SIZE_BYTES (16 * 1024 * 1024)
#endif

// --- RP2350 VARIANT ---
// This means RP2350B.
#define PICO_RP2350A 0

pico_board_cmake_set_default(PICO_RP2350_A2_SUPPORTED, 1)
#ifndef PICO_RP2350_A2_SUPPORTED
#define PICO_RP2350_A2_SUPPORTED 1
#endif