TMS320F28377S: Computational cost of the natural log function. Computationally efficient way to implement it.

Asad Hameed

We need to perform around a dozen conversions of raw thermistor voltages to temperatures. Going with Steinhart and Hart equation requires performing natural log. We understand that natural log is only available using math.h library (i.e. no hardware support) but we don't have idea about its computational complexity. This knowledge will be helpful to evaluate it against some other approaches such as curve fitting with a second or third order polynomial or using a lookup table. Please guide.

over 2 years ago

0 Sira Rao80 over 2 years ago

TI__Mastermind 27855 points

Asad,

TMU Type 1 - present in some C2000 devices - has a LOG2 (log to base 2) instruction that would make your computation very efficient (you can easily convert from log2 to ln). However, F28377S has TMU Type 0, which does not support the LOG2 instruction.

If you have to use F28377S in your design, it would be good to benchmark how many cycles the compiler RTS library function takes, and compare it with alternatives.

Thanks,

Sira

0 Asad Hameed over 2 years ago in reply to Sira Rao80

Intellectual 725 points

Thankyou for the reply. I think that we can close the ticket.

0 Sira Rao80 over 2 years ago in reply to Asad Hameed

TI__Mastermind 27855 points

Thanks for confirming.

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TMS320F28377S: Computational cost of the natural log function. Computationally efficient way to implement it.