Hello,

> But how does it actually work ? What means "blocking interrupt at some

See below. 

> level" ? I'm attaching ISA interrupt handler at IPL_SERIAL level so
> i call splserial() to "block" interrupts of my level and after
> tsleep() returns i unblock them. Ok, seems to work. But "man spl"
> says that:
> ------
> splserial()      blocks hard interrupts from serial interfaces (IPL_SERI-
> [...]
> ------
> 
> i.e. as i understand, *all* interrupts of this level including RS232
> ports etc are blocked.

Yes.

> ------
>     /* save old mask, block serial */
>     s = splserial();
> 
>     /* request interrupt */
>     dev_request_interrupt(sc);
> 				[1]
>     print("tralala\n");
>     tsleep(sc);		[2]
>     /* restpre old mask */
>     splx(s);
> ------

[1] The interrupt is masked/blocked, you will not be bothered by your
interrupt handler. You may safely manipulate data shared with the
handler etc.

[2] ltsleep() -> mi_switch() -> cpu_switch()
The cpu_switch routine (temporarily?) lowers SPL to zero (calling
spl0() or splx(SPL_NONE)), your handler gets chance to run and
eventually awaken your process (returning from tsleep()).

Well, that's what I found going through kern/kern_synch.c and
Arch/arm/ code... no warranty ;-)

	HTH,
		-- Jachym Holecek