TMS320F2800137: log() and logf() shows different calculation result

Hi,

Our Subject matter expert is OOO till 17th March. Please expect delayed response

Regards,

Subham

Ted,

Is fp_mode = relaxed in your CCS project compiler settings? I suspect logf is getting implemented using the TMU, and the input range is out of the range that the TMU can accurately handle.

Can you let me know what the input value is?

The LOG2F32 and IEXP2F32 TMU instructions are accurate for a specific range of inputs. I can provide details on this range if needed.

Thanks,

Sira

Hi Sira,

in logf(), the value is 8250.0f * ((4095.0f / adc_val) - 1.0f)) / 47000.0f and adc_val was 560. so the inside of logf is 1.108045.

i don't think it is out of range. could you check?

-O 2, -mf 3, --fp_mode relaxed, --fp_reassoc on

compiler is TI v22.6.1.LTS

Hi Ted,

Let me try this out at my end and see if I can reproduce the issue. Please give me a day.

Thanks,

Sira 

Ted,

What is your TMU setting set to?

Also, please show me the generated disassembly for the logf() based operation.

Thanks,

Sira

tmu is set as tmu1. is this the TMU setting?

about disassembly, I will update it soon.

Ted