IF statement compiles incorrectly

Teddy13640

Other Parts Discussed in Thread: TMS320F28335

Hello,

I am having trouble with the simplest of structures. A simple IF statement compiles incorrectly.
Below is the mixed assembly / source output from CC Studio Version 3.3.83.19. IDE 5.98.0.419. I'm
compiling for the TMS320F28335 on the with the experimenter kit. The branch statement is
never generated following the compare and thus the statement within the IF statement is executed in the code below.

Teddy

over 15 years ago

0 Lori Heustess over 15 years ago

TI__Guru* 91940 points

The CMP instruction sets flags based on the result of the comparison. The MOVB within the if is conditional and will only occur if the flags indicate LO (lower) is true.

-Lori

0 Teddy13640 over 15 years ago in reply to Lori Heustess

Prodigy 200 points

A MOV with a jump, never saw that before. What threw me was that I would single step into both branches of the IF statement. That just didn't look right!

Thanks for the information.

Teddy

0 Chris Chorley over 15 years ago in reply to Teddy13640

Prodigy 80 points

It is confusing at C level in a debugger though (CCS V4), as "t = 1" appears to be executed, but has no effect. If there are multiple statements with the 'if' block then a branch is used, and the debugger steps over them (as expected).

0 Lori Heustess over 15 years ago in reply to Teddy13640

TI__Guru* 91940 points

Just to make sure - it isn't really a jump. The instruction is always executed - it is just the outcome that depends on the condition. If the condition is true, then the move occurs. If the condition is false, no move. I can see how it is confusing from a C standpoint as the instruction is always executed. This is much more efficient than a branch which takes multiple cycles.

-Lori

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IF statement compiles incorrectly