CCS/TMS320F28335: One issue about using delay_us

Hao Wen

Prodigy 200 points

Part Number: TMS320F28335

Tool/software: Code Composer Studio

Hello,

I am using function delay_us to delay 700 ns. And I use it like this

float32 pulse1=0.7;

DELAY_US(pulse1);

But the actual delay for waveform on the scope is about 10 us. I am wondering why is that. And if I use DELAY_US(0.7); the delay is almost correct. Thank you.

over 8 years ago

0 Whitney Dewey over 8 years ago

TI__Guru 54195 points

Hello,

DELAY_US() is a macro, so when you pass it a constant (0.7), the compiler can evaluate the macro's calculation at compile time. However, when you pass it a variable (pulse1), the compiler can't do the calculation at compile time (because the value of pulse1 could change), and so it has to be calculated by the CPU. The time that is being spent calculating what to pass to F28x_usDelay() is what's causing the difference.

Whitney

0 Hao Wen over 8 years ago in reply to Whitney Dewey

Prodigy 200 points

Hello,

Thanks for your reply. Is there a way I can solve this when I would like to pass it a variable? Thank you.

0 Whitney Dewey over 8 years ago in reply to Hao Wen

TI__Guru 54195 points

Changing the DELAY_US() macro so that it casts A and CPU_RATE to float instead of long double might speed things up a little bit, but probably not enough.

Whitney

C2000™︎ microcontrollers

C2000 microcontrollers forum

CCS/TMS320F28335: One issue about using delay_us