pico_multicore breaks BTstack TLV persistence

[diegoparrilla]

I think I’ve found a reproducible combination that breaks TLV persistence in BTstack on RP2040 when using pico-sdk 2.2.0.
This can make developers struggle to locate the root cause, so I’m documenting it here.

The key point: just linking pico_multicore is enough to break TLV persistence, even if no multicore functions are called.

How to reproduce

In CMakeLists.txt:

# Link libraries required for the project
target_link_libraries(${PROJECT_NAME} PRIVATE
    ${LINK_LIBRARIES}
    pico_multicore
    <other libraries...>
)

To ensure the TLV does not overlap with other flash sections (only BT_TLV matters here):

MEMORY
{
    FLASH(rx) : ORIGIN = 0x10000000, LENGTH = 1152k
    RAM(rwx) : ORIGIN =  0x20000000, LENGTH = 256k
    SCRATCH_X(rwx) : ORIGIN = 0x20040000, LENGTH = 4k
    SCRATCH_Y(rwx) : ORIGIN = 0x20041000, LENGTH = 4k
    CONFIG_FLASH(rwx): ORIGIN = 0x101DE000, LENGTH = 120K
    GLOBAL_LOOKUP_FLASH(rwx): ORIGIN = 0x101FC000, LENGTH = 4K
    GLOBAL_CONFIG_FLASH(rwx): ORIGIN = 0x101FD000, LENGTH = 4K
    BT_TLV(rwx): ORIGIN = 0x101FE000, LENGTH = 8K
}

I’m using the Bluepad32 library, but the issue is reproducible using the BTstack included in pico-sdk.

Observed behavior

With this setup, any BTstack API call that must persist data in the TLV fails silently.
Nothing is stored.

A clear symptom: link keys are not persisted after pairing a Bluetooth keyboard/mouse, so the device cannot reconnect after a power cycle.

Key findings

• If I remove pico_multicore, TLV persistence works as expected.
• If I add pico_multicore but also launch code on Core 1 using multicore_launch_core1(), TLV persistence also works.

So the failure only occurs in the specific situation where:

pico_multicore is linked
AND core1 is NOT launched

This suggests initialization side effects in pico_multicore that interfere with flash operations BTstack depends on.

My project (still WIP): https://github.com/sidecartridge/rp2-atarist-rpikb

Hope this helps identify the root cause, or at least warns other developers about this combination.

[peterharperuk]

What's VLT? pico_btstack uses flash_safe_execute. There's some advice in the SDK about using pico_multicore. You might need to set PICO_FLASH_ASSUME_CORE0_SAFE=1

See https://github.com/raspberrypi/pico-sdk/blob/master/src/rp2_common/pico_flash/include/pico/flash.h#L12

[diegoparrilla]

Sorry, TLV (fixed): https://bluekitchen-gmbh.com/storing-link-keys-in-flash-memory/

I use the PICO_FLASH_ASSUME_COREx_SAFE in my code for Core 1, and I previously tested the following combinations (I chased the issue for a while):

1. No PICO_FLASH_ASSUME_CORE0_SAFE or PICO_FLASH_ASSUME_CORE1_SAFE macros set
2. PICO_FLASH_ASSUME_CORE1_SAFE set to 1, PICO_FLASH_ASSUME_CORE0_SAFE not set
3. PICO_FLASH_ASSUME_CORE1_SAFE set to 1, PICO_FLASH_ASSUME_CORE0_SAFE set to 1

The problem comes from just linking the library. PICO_FLASH_ASSUME_COREx_SAFE does not affect the outcome in this case.

[peterharperuk]

Thanks. Did you try setting PICO_FLASH_SAFE_EXECUTE_PICO_SUPPORT_MULTICORE_LOCKOUT to zero?

[diegoparrilla]

Yes. No luck.

[Loc15]

I can confirm this issue. On debug build I get assertion "false" failed: file ".../pico-sdk/src/rp2_common/pico_flash/flash.c", line 190, function: default_enter_safe_zone_timeout_ms using multicore (It works fine without it). On release build, it fails to store device using TLV persistence using multicore too.