Hello,
I am using CCSV5. I have a problem. The sprintf( ) function does not work for float or "%f". I am using MSP430G2553 MCU.
Please help.
Regards
Hi Guru!
GURU MOORTHY said:please guide how to do that
To change the settings, right-click on your project in the Project Explorer and select Properties:
You can also simply press ALT+ENTER. Then this window opens:
Go to (CCS) Build -> MSP430 Compiler -> Advanced Options -> Library Function Assumptions and change the Level of printf support to full for using floating point values.
GURU MOORTHY said:i am using msp430g2553. Will it be possible to use sprintf?
No, I would not use sprintf with floating point values on that small processor. I made an example for you - this is the code:
#include <msp430g2553.h>
#include <stdint.h>
#include <stdio.h>
#define VOLTAGE_V 1.234
char buffer[50];
uint8_t nr_of_chars;
void main( void )
{
WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer
nr_of_chars = sprintf( buffer, "The sensor voltage is %.3f V", VOLTAGE_V );
while( 1 );
}
This program writes the given text and the converted floating point value with three decimal places to the buffer, adds the string terminator \0 and it stores the number of the written characters (without the termination character) to the variable.
Content of buffer:
The sensor voltage is 1.234 V\0
Content of nr_of_chars:
29
As you can see, I pass the floating point value VOLTAGE_V (1.234) to the sprintf function. Full support for printf is enabled. The problem:
As you can see, the code size is 15,746 bytes. The MSP430G2553 has 16k of flash. Your MSP430 is already full!
Now consider if you really need to use floats. In the given example you could use mV instead of V and set the printf support to minimal. Now without using floating point - imagine you had multiplied your floating point value of 1.234 by 1000, resulting in 1234 integer only. This is the new code:
#include <msp430g2553.h>
#include <stdint.h>
#include <stdio.h>
#define VOLTAGE_MV 1234
char buffer[50];
uint8_t nr_of_chars;
void main( void )
{
WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer
nr_of_chars = sprintf( buffer, "The sensor voltage is %d mV", VOLTAGE_MV );
while( 1 );
}
Content of buffer:
The sensor voltage is 1234 mV\0
Content of nr_of_chars:
29
Now I use the unsigned integer and %d instead of %.3f for the sprintf function. The result in code size:
This is a difference, isn't it?
Of course you could now think if you need sprintf at all because you can also implement this functionality on your own, at least for this simple example, but this depends on your program. To convert 1234 to ASCII chars, you can do the following:
value = 1234; thousands = (value / 1000) + 48; value %= 1000; hundreds = (value / 100) + 48; value %= 100; tens = (value / 10) + 48; ones = (value % 10) + 48;
The +48 is the conversion from decimal to ASCII.
Dennis
That code size is with the Output Format of the compiler set to "eabi (ELF)". The EABI output format has the type single as 32-bits and double as 64-bits, and so the floating point support for the sprintf function has to support 64-bit floating point calculations.Dennis Eichmann said:As you can see, I pass the floating point value VOLTAGE_V (1.234) to the sprintf function. Full support for printf is enabled. The problem:
As you can see, the code size is 15,746 bytes. The MSP430G2553 has 16k of flash. Your MSP430 is already full!
If the Output Format is changed to "legacy COFF" then the code size taken by the example reduces to 10,030 bytes. This is because with the COFF output format the double type is 32-bits, meaning the floating point support for the sprintf function only has to support 32-bit floating point calculations.
Agree that on memory constrained devices such as the MSP430G2553 use of floating point calculations is not recommended, due to the size of run time support code required for the software floating-point operations.
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