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Memory problems idata

Christopher Holland

Hi Ken,

I understand that the 8051 has 256 bytes of internal data. Well, after declaring variables and array's, I get the error

	*** ERROR 107: ADDRESS SPACE OVERFLOW
	    SPACE: DATA
	    SEGMENT: _DATA_GROUP_
	    LENGTH: 0062H
	Target not created

Ok. So, I declare the variables using idata,
Which clears up the Error and allows access to the entire 256 bytes.

Well, the program compiles just fine, but the program is buggy. I'm not sure what the exact problem is, but I know the problem
has to do with memory and not in the code. I know the problem
is in the Memory, because If I delete some of the idata, the
program works. I really don't want to do that. I would like to
be able to use the maximum amount of internal data, but not have
any problems. I just have no how I can.
I must be over-writing memory, but I really shouldn't be.
Do you know what the problem could be?

I don't think the problem lies in variable access time.
I have the following statements,
which doesn't print out the correct MAC adress.
	GetMACInput(strSrcDest);
	printf("MAC Address......... ");
	printf("%02X:", strSrcDest->SrcMAC1 >> 8);
	printf("%02X:", strSrcDest->SrcMAC1 & 0x00FF);
	printf("%02X:", strSrcDest->SrcMAC2 >> 8);
	printf("%02X:", strSrcDest->SrcMAC2 & 0x00FF);
	printf("%02X:", strSrcDest->SrcMAC3 >> 8);
	printf("%02X",  strSrcDest->SrcMAC3 & 0x00FF);
	printf("\r\n");

P.S. I have no xdata just yet.
I plan on upgrading to a PSD (Flash/Sram/Eeprom) chip soon.

Thanks for your help,

Christopher J. Holland
8444 Capricorn Way #2
San Diego, CA. 92126
http://home.san.rr.com/webmain
I listen to doors and look at windows
"Holland is so low, that it is only saved by being damned'

Parents
  • 0 in reply to Christopher Holland

    "Am I to understand that I don't necessarily have access to the entire 256 bytes, but less than 256 bytes due to Stack Size/ Nesting and interrupt context saving?"

    Yes, you can't use all the idata space. The stack needs some of it.


    ">>...the stack resides in internal RAM too,
    >>positioned after IDATA up to the end of
    >>internal RAM"

    What Dan meant was that the stack starts in idata above your idata variables.


    "I am curious about Function calls and the space required. Do the nested Functions require Ram Space? Is there a difference between void Func1() and int Func1()?"

    For every function nesting the return address (two bytes) is pushed onto the stack. Interrupt service routines (sometimes) push considerably more data (PSW, registers etc) onto the stack. Values aren't returned from functions on the stack so there is no difference between int and void in this context.

    "I'm not exactly sure what interrupt context means. I am using an interrupt"

    When the ISR is called the 'context' of the uc is saved. The 'context' is the contents of any registers that will be changed in the ISR, so that they can be restored on exit.

    "I wish the compiler would have complained. The program compiles just fine"

    It would be very difficult if not impossible for the compiler to calculate worst case stack usage. You'll have to do that yourself!

    Stefan

Reply
  • 0 in reply to Christopher Holland

    "Am I to understand that I don't necessarily have access to the entire 256 bytes, but less than 256 bytes due to Stack Size/ Nesting and interrupt context saving?"

    Yes, you can't use all the idata space. The stack needs some of it.


    ">>...the stack resides in internal RAM too,
    >>positioned after IDATA up to the end of
    >>internal RAM"

    What Dan meant was that the stack starts in idata above your idata variables.


    "I am curious about Function calls and the space required. Do the nested Functions require Ram Space? Is there a difference between void Func1() and int Func1()?"

    For every function nesting the return address (two bytes) is pushed onto the stack. Interrupt service routines (sometimes) push considerably more data (PSW, registers etc) onto the stack. Values aren't returned from functions on the stack so there is no difference between int and void in this context.

    "I'm not exactly sure what interrupt context means. I am using an interrupt"

    When the ISR is called the 'context' of the uc is saved. The 'context' is the contents of any registers that will be changed in the ISR, so that they can be restored on exit.

    "I wish the compiler would have complained. The program compiles just fine"

    It would be very difficult if not impossible for the compiler to calculate worst case stack usage. You'll have to do that yourself!

    Stefan

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