[avr-gcc-list] Re: USART interrupts

[Bob Halford]

This is most likely an FAQ but it would seem (with the mega8 at least) 
that you
have to use SIGNAL rather than INTERRUPT for SIG_UART_RECV as
the code produced by the C-compiler does not read the UDR until after 
whole bunch
of registers have  been pushed on the stack..... Difficult to say with 
the limited
in-circuit tools to hand but my guess is that when using INTERRUPT, as 
soon as the
interrupt is re-enabled, the un-cleared RXC flags immediately causes 
another interrupt
and so on until the stack is full.

Is this really what happens? If so, surely this is a bug.... the 
interrupt arbritation logic
should not allow this (ie one way of avoiding this is to make the 
interrupt transition
rather than level sensitive.. but preferable is to disallow recursive 
interrupts).

You can kind of work round the problem by using SIGNAL and doing an 
sei() just after
reading the UDR but does this mean that if the SIG_UART_RECV s/r does 
not get done
before the next RXC, we are in the shit?

Cheers, Bob