Fix embassy hangs

[andelf]

Needs more investigation.

At least x035 works now.

Fix #71

[mwanner]

@andelf I can confirm this fixes the blinky examples that use embassy. At least for three devices I tested successfully: ch32v302, ch32x035, and ch32l103.

However, I think this means the entire comment above the function is wrong and needs to be corrected.

I added debug outputs in the two relevant init routines and tried all four variants for configuring WFITOWFE and SEVONPEND. And embassy based blinking only ever worked with both enabled (following from a ch32l103, but other chips showed same results):

no good, no LED blinking:

2024-11-30 23:27:01.044: post qingke_setup_interrupts state: (00000000)
2024-11-30 23:27:01.050: after ch32-hal embassy init:        (00000010)

2024-11-30 23:27:39.990: post qingke_setup_interrupts state: (00000000)
2024-11-30 23:27:39.996: after ch32-hal embassy init:        (00000000)

2024-11-30 23:28:04.196: post qingke_setup_interrupts state: (00000008)
2024-11-30 23:28:04.202: after ch32-hal embassy init:        (00000008)

All good on ch32l103, LED blinking:

2024-11-30 23:28:19.617: post qingke_setup_interrupts state: (00000008)
2024-11-30 23:28:19.623: after ch32-hal embassy init:        (00000018)

[honsunrise]

ch32v203 is also working.

[honsunrise]

Embassy uses WFE in RISC-V to put the processor to sleep. According to the WCH manual, the events that can wake up sleep caused by the WFE instruction come from three sources:

1. Enable an interrupt in the peripheral register, but do not enable this interrupt in the PFIC, while enabling the SEVONPEND bit in the PFIC.
2. Enable an EXTI channel as an event channel.
3. The interrupt configured in the PFIC.

At that time, based on the current situation, it seems that the 3 does not work, and the 1 also seems to be different from the description. Whether the corresponding interrupt is enabled in the PFIC does not seem to affect the effects of the SEVONPEND bit.

Perhaps the manual is incorrect?

[mwanner]

ch32v203 is also working.

Sorry, typo in my comment above: I meant to write v203, there is no v302 (AFAIK anyway).

[Dummyc0m]

FWIW embassy-rs/embassy@9e6e09a

[andelf]

I plan to merge this after addressing the comment fixes. This update will resolve issues with the blinky example and other lower-speed peripherals. And it does not block the spin-executor. @Dummyc0m