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global variables

 
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hundil
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global variables
PostPosted: Thu Jun 10, 2004 8:29 am     Reply with quote
My Question is very short;

In CCS, Global variables are to be considered as =0 in the beginning,
Or assigned to be any value.
If so, what is the fonction of zero_ram command

thanks for repliers

hundil
SherpaDoug



Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA

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PostPosted: Thu Jun 10, 2004 9:49 am     Reply with quote
I have never assumed ANY variables are zero at start-up unless the chip datasheet says so. Ideally zero_ram would never be needed but with the inevitability of bugs it is possible for the CPU to read a ram location that was never written to, with unpredictable results. Using zero_ram fills all of memory with zero before boot. This can help mitigate "flakey" problems that are hard to eliminate. If your program requires zero_ram to work, it has a problem. Zero_ram doesn't fix problems, it just hides them. But sometime hiding a problem will get you through the day....
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Ttelmah
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Re: global variables
PostPosted: Thu Jun 10, 2004 10:12 am     Reply with quote
hundil wrote:
My Question is very short;

In CCS, Global variables are to be considered as =0 in the beginning,
Or assigned to be any value.
If so, what is the fonction of zero_ram command

thanks for repliers

hundil

Zero_ram, ensures that _all_ variables (including non_global ones) will start at zero. Personally, it is quicker, and safer, to code your variale declarations to have the values you want, and only leave 'undeclared' variables that receive values as their first operation. However if you don't want to do this, zero_ram gives you a 'known' starting point, but at the cost of quite a long initialisation sequence. Note that the exact behaviour of variables, has changed slightly with compiler versions, and currently the manual only says that variables declared with the 'static' keyword are initialised to 0 by default. If you want to check how the compiler currently behaves, set up one simple variable of each type, and check what is actually done during initialisation.

best Wishes
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