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Hi,
I need to put a statement in a interrupt routine to shift a variable right one-bit. Like this:
dat >>=1;
It generated assembly code like this:
MOV A,dat CLR C RRC A MOV dat,A
What statement in C language sould be written to complete the shift operation but not effect the "C,carry" bit?
This is to save the "PUSH PSW", "POP PSW" instruction in my ISR. The inline assembly statement is not good to me, since I am not familar with it.
Thanks, John
I'm forced to find a way to save the time as more as I can.
In that case, you'll have to dive into assembly.
The compiler does several things that usually don't mix well with tight timing constraints in interrupts.
For example, it always locates the ISR somewhere in program memory, and performs a LJMP from the interrupt vector table to the start address of the ISR, even though there are 8 bytes available in the vector table that can hold a complete (yet short) interrupt service routine.
In that case, you'll have to dive into assembly. I agree now. It is the last thing I can do after I re-contrust the data structure to eliminate more control statement.
So far, it is hard to keep the state machine tight and clear.