Spin polls the raw executor and never sleeps. It is useful for disabling
any power features associated with wfi/wfe-like instructions.
When implementing support for the CH32V30x MCU, the wfi instruction
had issues interacting with the USB OTG peripheral and appeared to be
non-spec-compliant.
1. When sending a USB Data-in packet, the USB peripheral appears to be
unable to read the system main memory while in WFI. This manifests in
the USB peripheral sending all or partially zeroed DATA packets.
Disabling WFI works around this issue.
2. The WFI instruction does not wake up the processor when MIE is
disabled. The MCU provides a WFITOWFE bit to emulate the WFE instruction
on arm, which, when enabled, ignores the MIE and allows the processor to
wake up. This works around the non-compliant WFI implementation.
Co-authored-by: Codetector <codetector@codetector.org>
Co-authored-by: Dummyc0m <y@types.moe>
This introduces a `Pender` struct with enum cases for thread-mode, interrupt-mode and
custom callback executors. This avoids calls through function pointers when using only
the thread or interrupt executors. Faster, and friendlier to `cargo-call-stack`.
`embassy-executor` now has `arch-xxx` Cargo features to select the arch and to enable
the builtin executors (thread and interrupt).
