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rp: fix spinlocks staying locked after reset.

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Fixes #1736
This commit is contained in:
Dario Nieuwenhuis 2024-05-24 20:04:14 +02:00
parent 891ec5fa5d
commit 33bdc9e85f
1 changed files with 44 additions and 0 deletions
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44
embassy-rp/src/lib.rs
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@ -352,6 +352,50 @@ pub fn init(config: config::Config) -> Peripherals {
peripherals
}
#[cfg(feature = "rt")]
#[cortex_m_rt::pre_init]
unsafe fn pre_init() {
// SIO does not get reset when core0 is reset with either `scb::sys_reset()` or with SWD.
// Since we're using SIO spinlock 31 for the critical-section impl, this causes random
// hangs if we reset in the middle of a CS, because the next boot sees the spinlock
// as locked and waits forever.
//
// See https://github.com/embassy-rs/embassy/issues/1736
// and https://github.com/rp-rs/rp-hal/issues/292
// and https://matrix.to/#/!vhKMWjizPZBgKeknOo:matrix.org/$VfOkQgyf1PjmaXZbtycFzrCje1RorAXd8BQFHTl4d5M
//
// According to Raspberry Pi, this is considered Working As Intended, and not an errata,
// even though this behavior is different from every other ARM chip (sys_reset usually resets
// the *system* as its name implies, not just the current core).
//
// To fix this, reset SIO on boot. We must do this in pre_init because it's unsound to do it
// in `embassy_rp::init`, since the user could've acquired a CS by then. pre_init is guaranteed
// to run before any user code.
//
// A similar thing could happen with PROC1. It is unclear whether it's possible for PROC1
// to stay unreset through a PROC0 reset, so we reset it anyway just in case.
//
// Important info from PSM logic (from Luke Wren in above Matrix thread)
//
// The logic is, each PSM stage is reset if either of the following is true:
// - The previous stage is in reset and FRCE_ON is false
// - FRCE_OFF is true
//
// The PSM order is SIO -> PROC0 -> PROC1.
// So, we have to force-on PROC0 to prevent it from getting reset when resetting SIO.
pac::PSM.frce_on().write(|w| {
w.set_proc0(true);
});
// Then reset SIO and PROC1.
pac::PSM.frce_off().write(|w| {
w.set_sio(true);
w.set_proc1(true);
});
// clear force_off first, force_on second. The other way around would reset PROC0.
pac::PSM.frce_off().write(|_| {});
pac::PSM.frce_on().write(|_| {});
}
/// Extension trait for PAC regs, adding atomic xor/bitset/bitclear writes.
trait RegExt<T: Copy> {
#[allow(unused)]