CCS/MSP430G2553: Variable multiplication giving false output

Jeevan Thomas

Part Number: MSP430G2553

Tool/software: Code Composer Studio

I want to multiply two ADC readings (voltage and current to get power). I am using CCS7 version and I enabled the hardware multiplier in CCS project properties, compiler and linker(set to 16).

But the result in the watch window is nowhere near the actual answer. If I try to multiply two variables, the result i am getting is '314' for any value of the variables. And if try to multiply one variable(value 45) with a constant, i can not increase the value of the constant more than the number 32, when ever it goes more than 32, the result becomes '314'. If I multiply two constant numbers, whose product is less than 32768, i am getting the right answer.

Am I missing any settings..??

The variable declaration and multiplication portion is as given below

unsigned int adc_val[6]={0,0,0,0,0,0};
unsigned int v_pan_avg_acc_n10=0,c_pan_avg_acc_n10=0,v_pan_avg_n7=0,c_pan_avg_n7=0;
unsigned int panel_pwr_n14=0;

------------------------------------------------------

-----------------------------------------------------

v_pan_avg_acc_n10 = v_pan_avg_acc_n10+adc_val[4];

c_pan_avg_acc_n10 = c_pan_avg_acc_n10+adc_val[1];

adc_count++;

if(adc_count>32)
{

v_pan_avg_n7 = v_pan_avg_acc_n10>>8;
....................................................................
c_pan_avg_n7 = c_pan_avg_acc_n10>>8;

panel_pwr_n14 = (v_pan_avg_n7) * (c_pan_avg_n7 );

..................................................................

.................................................................

}

over 7 years ago

0 Cameron LaFollette over 7 years ago

TI__Genius 14875 points

Hi Jeevan
Which variable is returning the incorrect answer? And which variable is static, or '32'?

Are you watching the values to make sure there is no overflow at any point?

0 Cameron LaFollette over 7 years ago in reply to Cameron LaFollette

TI__Genius 14875 points

A very easy test would be to try using a Long, if this fixes it, then you know you have roll over.

0 Jeevan Thomas over 7 years ago in reply to Cameron LaFollette

Prodigy 120 points

Hii..Thank you for the reply,
actually the variable which stores the product gives a false output always(panel_pwr_n14).
I tried all possible combinations of type def - int, short, unsigned int and long.
even i tried to do the calculations by _QMATH, still the multiplication gives false result.
I increased the stack size to 0x100 also.

0 Jeevan Thomas over 7 years ago in reply to Jeevan Thomas

Prodigy 120 points

In the CCS project properties I have set compiler and linker to '--use_hw_mpy' to '16', as my controller is 16bit.
Is this the only setting required to make the hardware multiplier to do the multiplication or any other settings required?

0 Keith Barkley over 7 years ago in reply to Jeevan Thomas

Guru 42145 points

Why are you dividing by 256 when you have only accumulated 33 values?

Show us some actual compilable code that shows the problem. You can just use an array of values to simulate the ADC.

0 Jeevan Thomas over 7 years ago in reply to Keith Barkley

Prodigy 120 points

The maximum value in the adc result will be 1023. If i want to multiply two of such adc results it will come 1023*1023, which i thought the controller may not be able to process, thats why i am converting the adc values normalized to a maximum of 2^7. And the product will come 2^14, which the controller should be able to handle.

Actually nothing shows an error or warning, i simulated using the values, intead of just giving values, i connected pots and applied a fixed voltage at adc to get the results. But the product i am getting is wrong in the watch window.

0 Cameron LaFollette over 7 years ago in reply to Jeevan Thomas

TI__Genius 14875 points

Ignore the reply I deleted, I didn't see where you had replied above.

Do you have a piece of test code which can replicate the issue, if so I can test it on my end.

0 Jeevan Thomas over 7 years ago in reply to Cameron LaFollette

Prodigy 120 points

#include <msp430g2553.h>

unsigned int adc_val[6]={700,600,0,0,0,0};
unsigned int x=0,y=0,z=0;

void main(void)
{
WDTCTL = WDTPW + WDTHOLD; // stop watchdog timer
DCOCTL = CALDCO_16MHZ; //Digital oscillator clock at 16MHz
BCSCTL1 = CALBC1_16MHZ; //SM clock at 16MHz
WDTCTL=WDT_MDLY_32; //2msec timer

while(1) //loop for ever
{
if((IFG1&BIT0)==0x01) //watchdog timer flag is set (timed for 2ms)
{
x = adc_val[0]>>3;
y = adc_val[1]>>3;
z = x *y ;
IFG1 &= ~WDTIFG; // Clear the interrupt flag for the WDT
}
}
}

expected calculation
x = 700>>3 = 87
y= 600>>3 = 75
z = x*y = 6525

0 Cameron LaFollette over 7 years ago in reply to Jeevan Thomas

TI__Genius 14875 points

This worked fine for me. You may want to use the default MPY options and see if that changes anything. If all else fails, try importing your code to a new project without changing any of the project settings.

0 Cameron LaFollette over 7 years ago in reply to Cameron LaFollette

TI__Genius 14875 points

Hi Jeevan,
I found your issue. The G2553 does not have a HW MPY. So the setting you're using is telling it to use an instruction that isn't there. To fix this, change the option you mentioned to none.

0 Jeevan Thomas over 7 years ago in reply to Cameron LaFollette

Prodigy 120 points

Hii sir,

sorry for the late reply, i was assigned to another project for a couple of days.

I have changed the setting as per your suggestion. now I am getting the results properly. Also I am getting a warning where ever I am doing a multiplication.

<a href="processors.wiki.ti.com/.../1533"> (ULP 6.1) Detected use of multiplication on a device that has no hardware
multiplier.

Thank you for your support, it was really helpful.

0 Cameron LaFollette over 7 years ago in reply to Jeevan Thomas

TI__Genius 14875 points

That's expected. It's just letting you know that the compiler will simulate the pultiplication algorithm because your device does not have an MPY.

**Attention** This is a public forum

MSP low-power microcontrollers

MSP low-power microcontroller forum

CCS/MSP430G2553: Variable multiplication giving false output