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//! Boot Select button
//!
//! The RP2040 rom supports a BOOTSEL button that is used to enter the USB bootloader
//! if held during reset. To avoid wasting GPIO pins, the button is multiplexed onto
//! the CS pin of the QSPI flash, but that makes it somewhat expensive and complicated
//! to utilize outside of the rom's bootloader.
//!
//! This module provides functionality to poll BOOTSEL from an embassy application.
use crate::Peri;
use crate::flash::in_ram;
/// Reads the BOOTSEL button. Returns true if the button is pressed.
///
/// Reading isn't cheap, as this function waits for core 1 to finish it's current
/// task and for any DMAs from flash to complete
pub fn is_bootsel_pressed(_p: Peri<'_, crate::peripherals::BOOTSEL>) -> bool {
let mut cs_status = Default::default();
unsafe { in_ram(|| cs_status = ram_helpers::read_cs_status()) }.expect("Must be called from Core 0");
// bootsel is active low, so invert
!cs_status.infrompad()
}
mod ram_helpers {
use rp_pac::io::regs::GpioStatus;
/// Temporally reconfigures the CS gpio and returns the GpioStatus.
/// This function runs from RAM so it can disable flash XIP.
///
/// # Safety
///
/// The caller must ensure flash is idle and will remain idle.
/// This function must live in ram. It uses inline asm to avoid any
/// potential calls to ABI functions that might be in flash.
#[inline(never)]
#[unsafe(link_section = ".data.ram_func")]
#[cfg(target_arch = "arm")]
pub unsafe fn read_cs_status() -> GpioStatus {
let result: u32;
// Magic value, used as both OEOVER::DISABLE and delay loop counter
let magic = 0x2000;
core::arch::asm!(
".equiv GPIO_STATUS, 0x0",
".equiv GPIO_CTRL, 0x4",
"ldr {orig_ctrl}, [{cs_gpio}, $GPIO_CTRL]",
// The BOOTSEL pulls the flash's CS line low though a 1K resistor.
// this is weak enough to avoid disrupting normal operation.
// But, if we disable CS's output drive and allow it to float...
"str {val}, [{cs_gpio}, $GPIO_CTRL]",
// ...then wait for the state to settle...
"2:", // ~4000 cycle delay loop
"subs {val}, #8",
"bne 2b",
// ...we can read the current state of bootsel
"ldr {val}, [{cs_gpio}, $GPIO_STATUS]",
// Finally, restore CS to normal operation so XIP can continue
"str {orig_ctrl}, [{cs_gpio}, $GPIO_CTRL]",
cs_gpio = in(reg) rp_pac::IO_QSPI.gpio(1).as_ptr(),
orig_ctrl = out(reg) _,
val = inout(reg) magic => result,
options(nostack),
);
core::mem::transmute(result)
}
#[cfg(not(target_arch = "arm"))]
pub unsafe fn read_cs_status() -> GpioStatus {
unimplemented!()
}
}
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