`esp32` - issue with `RSA` peripheral

[playfulFence]

Encountered a problem during implementing https://github.com/esp-rs/esp-hal/pull/790 : Program run hangs in this or similar blocks -> seems to be stuck in non-idle mode.

One idea where the problem is: Every other chip (except of esp32) has a separate register for handling IDLE state (RSA_IDLE_REG for esp32sX or RSA_QUERY_IDLE for esp32cX), but on esp32 it's checked through the interrupt register on which async functionality depends -> conflict

[playfulFence]

This one is still valid though. Made some tests on this code:

#[main]
async fn main(spawner: Spawner) -> ! {
    let peripherals = Peripherals::take();
    let system = SystemControl::new(peripherals.SYSTEM);
    let clocks = ClockControl::boot_defaults(system.clock_control).freeze();

    let mut rsa = Rsa::new_async(peripherals.RSA);

    test_modular_exponentiation(rsa).await;
    // test_modular_multiplication(rsa);
    // test_multiplication(rsa);

    loop {
    }
}

const fn compute_r(modulus: &U512) -> U512 {
    let mut d = [0_u32; U512::LIMBS * 2 + 1];
    d[d.len() - 1] = 1;
    let d = Uint::from_words(d);
    d.const_rem(&modulus.resize()).0.resize()
}

const fn compute_mprime(modulus: &U512) -> u32 {
    let m_inv = modulus.inv_mod2k(32).to_words()[0];
    (-1 * m_inv as i64 % 4294967296) as u32
}

async fn test_modular_exponentiation(mut rsa: Rsa<'static, Async>) {
    const EXPECTED_OUTPUT: [u32; U512::LIMBS] = [
        1601059419, 3994655875, 2600857657, 1530060852, 64828275, 4221878473, 2751381085,
        1938128086, 625895085, 2087010412, 2133352910, 101578249, 3798099415, 3357588690,
        2065243474, 330914193,
    ];

    #[cfg(not(feature = "esp32"))]
    {
        rsa.enable_disable_constant_time_acceleration(true);
        rsa.enable_disable_search_acceleration(true);
    }
    let mut outbuf = [0_u32; U512::LIMBS];
    let mut mod_exp = RsaModularExponentiation::<operand_sizes::Op512, esp_hal::Async>::new(
        &mut rsa,
        BIGNUM_2.as_words(),
        BIGNUM_3.as_words(),
        compute_mprime(&BIGNUM_3),
    );
    let r = compute_r(&BIGNUM_3);
    let base = &BIGNUM_1.as_words();
    mod_exp.exponentiation(&base, r.as_words(), &mut outbuf).await;
    assert_eq!(EXPECTED_OUTPUT, outbuf);
    esp_println::println!("Yep");
}

Output on esp32c6:

On esp32:

[playfulFence]

I don't see any "clean" way out of here. The whole async functionality depends on INTERRUPT register in RSA peripheral, which at the same time signalizes about the IDLE state of peripheral.

Maybe there's any option to add some simple "arbitration" (flag) like what event provoked the change of this reg. Just thoughts out loud anyways 😄

[jessebraham]

This is very low priority so I would not spend too much effort on it right now.

[playfulFence]

This is very low priority so I would not spend too much effort on it right now.

Yeah, for sure. I've only checked if this issue is still valid at all