Hi.
>
> Is there some documentation out there about the effect of all the AVR
> specific attributes? I'd like to understand the puposes and (generated
> code) consequences of
>
> OS_main
Function with "OS_main" and 'OS_task' attributes do not save any
"call-saved" registers.
1. "OS_main" attribute used when there IS guarantee that interrupts are
disabled at that time when function is called. For example "main" function in
avr-libc. If this function has local variables that a prologue will look so:
in r28, 0x3d ; 61
in r29, 0x3e ; 62
sbiw r28, 0x08 ; 8
out 0x3e, r29 ; 62
out 0x3d, r28 ; 61
> OS_task
2. "OS_task" attribute used when there is NO guarantee that interrupts are
disabled at that time when function is called. For example task functions
multi-threading operating systems. In this case save/clear/restore "I" flag is
need for changing SP register. Prologue (if this function has local variables)
will look so:
in r28, 0x3d ; 61
in r29, 0x3e ; 62
sbiw r28, 0x08 ; 8
in r0, 0x3f ; 63
cli
out 0x3e, r29 ; 62
out 0x3f, r0 ; 63
out 0x3d, r28 ;
> naked
From GCC manual:
naked
Use this attribute on the ARM, AVR, C4x and IP2K ports to indicate that the
specified function does not need prologue/epilogue sequences generated by the
compiler. It is up to the programmer to provide these sequences.
Anatoly.
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