Why I wrote an entire RP2350 SDK in pure ARM assembly

    .thumb_func
    .global main
main:
    @ ---- Clock tree bring-up ---------------------------------------------
    bl      xosc_init                       @ XOSC stable
    bl      pll_sys_150_mhz                 @ pll_sys = 150 MHz
    bl      pll_usb_48_mhz                  @ pll_usb = 48 MHz
    bl      clocks_init                     @ wire muxes
    bl      tick_init                       @ 1 MHz tick to TIMER0/1/WDG
    bl      watchdog_disable                @ explicit safe state

    @ ---- Peripheral init at the new clock rate ---------------------------
    bl      gpio_led_init                   @ LED on GP25
    bl      uart0_init                      @ wrong baud (computed for 12 MHz)
    bl      clocks_post_pll_uart_baud_fixup @ fix to 150 MHz divisors

    ldr     r0, =banner
    bl      uart0_puts

.Lloop:
    bl      gpio_led_toggle

    @ 3-cycle inner body (subs + bne) at 150 MHz = 20 ns / iteration.
    @ DELAY_COUNT = 12_500_000 -> 250 ms half-period -> ~2 Hz blink.
    ldr     r0, =DELAY_COUNT_150MHZ
1:  subs    r0, #1
    bne     1b

    b       .Lloop