🛠 Boot UF2, mode BOOTSEL et recovery d'une carte briquée

Objectives

Understand the RP2350 boot chain: the USB boot code resides in ROM and cannot be overwritten — making a Pico 2 nearly impossible to permanently brick. You will learn about BOOTSEL mode, the UF2 format, the picotool/MSD tools, and how to recover a card that no longer boots (bad firmware, RP2040 binary, misconfigured secure boot).

Hardware

• 1 × Raspberry Pi Pico 2 (optionally "bricked" on purpose)
• Micro-USB data cable; picotool (host build from the SDK or GitHub release)
• Optional: SWD debugger (CMSIS-DAP / pico-probe) for debugging without using the button

Full Code

/* saut_vers_bootsel.c — depuis le programme, retourne au mode UF2
   Utile pour un produit : mise a jour sans ouvrir le boitier. */
#include "pico/stdlib.h"
#include "pico/bootrom.h"

#define BTN_PIN 22

int main(void) {
    gpio_init(BTN_PIN); gpio_set_dir(BTN_PIN, GPIO_IN); gpio_pull_up(BTN_PIN);
    stdio_init_all;
    sleep_ms(2000);                       /* fenetre pour ouvrir le terminal */
    printf("Appui long sur GP22 -> mode BOOTSEL (lecteur RPI-RP2)\n");
    while (gpio_get(BTN_PIN)) sleep_ms(10);
    rom_reset_to_bootsel;               /* ne revient jamais */
}

Recovery procedure without code: 1) Hold BOOTSEL and plug in USB; 2) The RPI-RP2 drive appears (the ROM always responds); 3) Copy a valid UF2 (pico2!) to overwrite the flash; 4) The card restarts. Inventory: picotool info -a and picotool reboot -u (USB reboot) from any UF2 firmware.

Expected Verification

Regardless of what garbage is flashed (RP2040 binary, looping program, saturated RAM), holding BOOTSEL while plugging in makes the RPI-RP2 drive reappear, and a valid pico2 UF2 restores the card. picotool info displays the Pico 2 (RP2350) in USB boot mode.

Common Errors

• Believing the card is dead: if BOOTSEL produces the drive, the ROM is healthy — it is structurally impossible to brick via software (except for OTP).
• Copying a UF2 compiled for pico (RP2040): the card restarts into a void; redo BOOTSEL then flash a real pico2 build.
• Charge-only cable or finicky hub: the drive never appears, test another port/cable first.
• On Linux, forgetting udev permissions or using picotool load without an appropriate --boot2 when flashing raw binaries via SWD.
• Secure boot accidentally enabled in OTP: only a correctly signed firmware will restart — document your keys, OTP is irreversible.