Compiler/TM4C1290NCPDT: How to convert from value from int32_t to float on the tm4c1290ncpdt-128-tqfp

Haroldo Cazeao

Prodigy 200 points

Part Number: TM4C1290NCPDT

Tool/software: TI C/C++ Compiler

I'm having the hardest converting an int32_t to float. I didn't think it should be that hard.

For example, I have the following ratio:

signed int32 Numerator = 2

signed int32 Denominator = 583

Ratio = Numerator / Denominator = 0.003430 .

However, in the tm4c1290ncpdt-128-tqfp, Ratio = 0.000000 (always).

How do I get the right number?

over 7 years ago

0 Ralph Jacobi over 7 years ago

TI__Guru*** 135355 points

Hello Haroldo,

Until the variables are defined as float numbers, the result will be 0 because the division of 2 signed int32's will be treated as an integer operation and will not result in a floating point value. You need to define your numerator, denominator and ratio all as floats to get the result you desire.

0 Haroldo Cazeao over 7 years ago in reply to Ralph Jacobi

Prodigy 200 points

Hi Ralph,
thank you for your prompt reply. The question is now, how do I display the floating point values. I tried your regular %f. That didn't seem to work.
I would like to be able to display 6 digits after the decimal.
Thanks,

0 Ralph Jacobi over 7 years ago in reply to Haroldo Cazeao

TI__Guru*** 135355 points

Hello Haroldo,

Are you wanting to display them over UART? Or some other means?

0 Haroldo Cazeao over 7 years ago in reply to Ralph Jacobi

Prodigy 200 points

2 ways,
1st over USB with something like this usprintf((char *)usb_AppTxBuf, "\r\nt1: %u S1: %d\r\nt2: %u S2: %d\r\nHeating slope: (%x) %u.%04u\r\n",
2nd over the console using code composer IDE.
Thanks,

0 Ralph Jacobi over 7 years ago in reply to Haroldo Cazeao

TI__Guru*** 135355 points

Hello Haroldo,

I am not sure what we have to offer for the USB side, I need to investigate that further.

CCS Console wise, please see this past thread - I think it applies well for outputting to CCS Console (I saw other threads which talked about the CIO Function): https://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/t/469206

0 Haroldo Cazeao over 7 years ago in reply to Ralph Jacobi

Prodigy 200 points

Hi Ralph,
I would be interested in finding how to print float over the USB side.\
Thanks,

0 Ralph Jacobi over 7 years ago in reply to Haroldo Cazeao

TI__Guru*** 135355 points

Hello Haroldo,

I looked into this, and the best solution would be for you to convert the float before printing it.

There isn't a solution for printing float over USB available without the use of some sort of conversion that won't require heavy modification or development. It's just not something that has justified the effort required for development (given the conversion method that is functional) so we consider it to be an application specific demand.

In the past I offered an example of how to handle the conversion which you can read here: https://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/p/663530/2438264#2438264

Also this thread had some other discussions about printing floats: https://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/p/663933/2440707

If you want to develop something where conversion is not needed, then the best resource you could look at is this post from MSP430 which discusses how to reroute printf to use a UART output, though even that probably lacks support for the %f floating point designator: http://processors.wiki.ti.com/index.php/Printf_support_for_MSP430_CCSTUDIO_compiler#Rerouting_printf.28.29_output

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Compiler/TM4C1290NCPDT: How to convert from value from int32_t to float on the tm4c1290ncpdt-128-tqfp