LAUNCHXL-CC2640R2: Why does Display_printf default float values to 4 decimal places and no other format specifier works

Gerriko Iot

I am trying to use Display_printf to print float values to 1 decimal place but the format specifier "%.1f" for float does not work and all it is doing is print out values to 4 decimal places.

example:

By way of illustration, I simply amended the example given in the documentation.

Display_printf(displayHandle, 0, 0, "ADC: %d", adcValue); // works fine
Display_printf(displayHandle, 1, 0, "float: %.1f", adcValue/1.0); // does not work

over 8 years ago

0 Gerardo Gomez Martinez over 8 years ago

TI__Expert 5825 points

Hi,

What type of Display are you specifying when calling Display_open()?

And which version of the SDK are you using?

Thanks,
Gerardo

0 Gerriko Iot over 8 years ago in reply to Gerardo Gomez Martinez

Intellectual 300 points

I was using CCS Cloud.

Example uploaded into CCS Cloud is via dev.ti.com and clicking on SimpleLink CC2640R2 SDK icon.

I was following the first example provided in SimpleLink Academy:

http://dev.ti.com/tirex/#/?link=Software%2FSimpleLink%20CC2640R2%20SDK%2FSimpleLink%20Academy%2FOverview

This informed me to upload the "empty" example, which is found by left clicking on:

SimpleLink CC2640R2 SDK - v:1.40.00.45

-- Examples

--- TI Drivers

---- empty

Then refer to "Task 4 - Add ADC read" and "Task 5 - Add UART print"

In task 5 you will see it uses "Display_printf" to send information to UART

I amended this task to try out a float data type

0 Gerardo Gomez Martinez over 8 years ago in reply to Gerriko Iot

TI__Expert 5825 points

Hi,

The Display driver uses System_vsnprintf which is a lighter, faster implementation of vsnprintf but does not support the full range of format strings. From the System_printf documentation (http://rtsc.eclipse.org/cdoc-tip/xdc/runtime/System.html#printf) we can see that the precision specifier is not supported for float formats. If code size isn't important you can use sprintf() to convert the value to a string first and then use Display_printf() to display it. You do this as follows:

Add this at the top of the file:

#include <stdio.h>

Then convert to string and display:

char buffer[10];
sprintf(buffer, "%.1f", adcValue);
    
Display_printf(displayHandle, 1, 0, "float: %s", buffer);

Hope that helps,
Gerardo

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LAUNCHXL-CC2640R2: Why does Display_printf default float values to 4 decimal places and no other format specifier works