topic Re: changing in global variable value in 8-bit Microcontrollers

changing in global variable value - MC9S08GB60

santhu — Mon, 21 Jul 2008 13:10:27 GMT

hi,

I'm using HCS08 family controller(MC9S08GB60).In the code i'm using some global variables like x,y,z.The values of global variable changes as required.But while executing following statement (mathematical) the values of global variable changes to unknown value.The statement is as below

a=(unsigned long int)((vtg_r_max1 * vtg_r_max1)+(vtg_y_max1 * vtg_y_max1)+(vtg_r_max1 * vtg_y_max1));

b=(unsigned long int)((vtg_y_max1 * vtg_y_max1)+(vtg_b_max1 * vtg_b_max1)+(vtg_y_max1 * vtg_b_max1));

c=(unsigned long int)((vtg_b_max1 * vtg_b_max1)+(vtg_r_max1 * vtg_r_max1)+(vtg_b_max1 * vtg_r_max1));

The above statement is just in the form of (a2+b2+ab).And the global variable x,y,z have no relationship with this expression.

Can you suggest me the sollution for changes in global variable value upon executing each expression.

With regards

santhu

Added p/n to subject.

Message Edited by NLFSJ on 2008-07-24 07:28 AM

Re: changing in global variable value

bigmac — Mon, 21 Jul 2008 13:27:54 GMT

Hello Santhu

It is possible that the stack is over-writing the global variables. Are the variables in question located immediately below the stack allocation? The map file for the project should provide this information. With the calculations using long variables, the stack requirements could be extensive, and exceed the size you have allowed.

Try increasing the stack size to see whether this helps.

Regards,

Mac

Re: changing in global variable value

santhu — Mon, 21 Jul 2008 16:40:16 GMT

hi Mac,

Thanks for your suggestion.And now my code working properly.I increased my stack size from 50 to 100. While answering me,you used below words.

With the calculations using long variables, the stack requirements could be extensive, and exceed the size you have allowed.

Can you tell me what you mean by calculation using long variable.Is there is any calculation for increasing stack size.What is the max value we can give for stack in 8 bit controller of 64k.

With regards

santhu

Re: changing in global variable value

eckhard — Mon, 21 Jul 2008 17:04:29 GMT

Hello,

Codewarrior keeps local Variables on the Stack, so by using long, much stack space is used ( 4 Bytes for each long variable ). The max value for the stack size is given by the RAM size. For gte GB60 this is 4 KB.
You can use Stacktop instead of Stacksize to put the Stack to the Top of the RAM area.

Eckhard.