Re: [avr-libc-dev] wdt.h watchdog code - will an interrupt mess up the timing ?

[Joerg Wunsch]

As Jeff Kowing wrote:

> My concern is that since global interrupts are potentially
> re-enabled on line 5, what prevents an interrupt routine from
> triggering before line 6 gets executed ?  I believe that the
> instruction following a "sei" instruction is guaranteed to execute
> before any pending interrupts are handled, but is the same true when
> using an "in" instruction to set the I bit ?

Yes, it is, alas it's undocumented.  Any function prologue/epilogue
generated by GCC also relies on that.

> My other question concerns wdt_disable():

> 1. in __tmp_reg__, __SREG__
> 2. out _WD_CONTROL_REG, _BV(_WD_CHANGE_BIT) | _BV(WDE)
> 3. out _WD_CONTROL_REG, __zero_reg__
> 4. out __SREG__, __tmp_reg__

> This one really confuses me because there is no "cli" ...

And I think you've found a real bug here.  Originally, wdt_disable()
has been implemented in terms of _wdt_write(), but Eric Weddington
rewrote that in rev 1.11, to fix bug #11522.  Obviously, the cli got
lost in this.

Please file a bug report for that.

-- 
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)