I am programming a Raspberry Pi Pico in C. I have this MWE:

#include "pico/stdlib.h"
#include "pico/cyw43_arch.h"
#include "hardware/uart.h"

#define UART_ID uart0
#define BAUD_RATE 2000000
#define UART_TX_PIN 0
#define UART_RX_PIN 1

uint8_t blink_LED;

void handle_uart_commands() {
    // Function to be called when data is received in the UART.
    while (uart_is_readable(UART_ID)) {
        uint8_t ch = uart_getc(UART_ID);

        switch (ch) {
            case 'b':
                printf("%d", blink_LED); // This sends "0", ok!
                blink_LED = 7;
                printf("%d", blink_LED); // This sends "7", ok!
            break;
        }
    }
}

void init_uart(void) {
    uart_init(UART_ID, BAUD_RATE);
    gpio_set_function(UART_TX_PIN, UART_FUNCSEL_NUM(UART_ID, UART_TX_PIN));
    gpio_set_function(UART_RX_PIN, UART_FUNCSEL_NUM(UART_ID, UART_RX_PIN));

    // Set up a RX interrupt:
    int UART_IRQ = UART_ID == uart0 ? UART0_IRQ : UART1_IRQ; // Select correct interrupt for the UART we are using.
    irq_set_exclusive_handler(UART_IRQ, handle_uart_commands);
    irq_set_enabled(UART_IRQ, true);
    uart_set_irq_enables(UART_ID, true, false);
}

void init_stuff(void) {
    stdio_init_all();
    init_uart();
    hard_assert(cyw43_arch_init() == PICO_OK);
    blink_LED = 3;
}

int main() {
    init_stuff();

    while (true) {
        if (blink_LED) {
            cyw43_arch_gpio_put(CYW43_WL_GPIO_LED_PIN, 1);
            sleep_ms(333);
            cyw43_arch_gpio_put(CYW43_WL_GPIO_LED_PIN, 0);
            sleep_ms(333);
            blink_LED -= 1;
            printf("b"); // Indicate that the LED blinked once.
        }
    }
}

What it is supposed to do:

1. Blink the LED 3 times upon power on.
2. Upon receiving b through the UART serial communication, it should blink the LED 7 times.

What it does:

1. Blinks the LED 3 times upon power on. Ok!
2. Upon receiving b, the LED does not blink a single time. Not ok.

I added the two printf lines just to see the value of blink_LED, and it sends the right values, meaning it is receiving and correctly processing b. However, the LED does not blink. Moreover, the printf("b") line is only executed 3 times after power on, meaning it never goes back into the if (blink_LED). I don’t understand why. Is the value of blink_LED=7 somehow only valid within handle_uart_commands and after that it returns to the previous value?