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/**********************************************************************

 *

 * Filename:    memtest.c

 *

 * Description: General-purpose memory testing functions.

 *

 * Notes:       This software can be easily ported to systems with

 *              different data bus widths by redefining 'datum'.

 *

 *

 * Copyright (c) 1998 by Michael Barr.  This software is placed into

 * the public domain and may be used for any purpose.  However, this

 * notice must not be changed or removed and no warranty is either

 * expressed or implied by its publication or distribution.

 **********************************************************************/

#include "memtest.h"

/**********************************************************************

 *

 * Function:    memTestDataBus()

 *

 * Description: Test the data bus wiring in a memory region by

 *              performing a walking 1's test at a fixed address

 *              within that region.  The address (and hence the

 *              memory region) is selected by the caller.

 *

 * Notes:

 *

 * Returns:     0 if the test succeeds.

 *              A non-zero result is the first pattern that failed.

 *

 **********************************************************************/

datum

memTestDataBus(volatile datum * address)

{

    datum pattern;

    /*

     * Perform a walking 1's test at the given address.

     */

    for (pattern = 1; pattern != 0; pattern <<= 1)

    {

        /*

         * Write the test pattern.

         */

        *address = pattern;

        /*

         * Read it back (immediately is okay for this test).

         */

        if (*address != pattern)

        {

            return (pattern);

        }

    }

    return (0);

}   /* memTestDataBus() */

/**********************************************************************

 *

 * Function:    memTestAddressBus()

 *

 * Description: Test the address bus wiring in a memory region by

 *              performing a walking 1's test on the relevant bits

 *              of the address and checking for aliasing. This test

 *              will find single-bit address failures such as stuck

 *              -high, stuck-low, and shorted pins.  The base address

 *              and size of the region are selected by the caller.

 *

 * Notes:       For best results, the selected base address should

 *              have enough LSB 0's to guarantee single address bit

 *              changes.  For example, to test a 64-Kbyte region,

 *              select a base address on a 64-Kbyte boundary.  Also,

 *              select the region size as a power-of-two--if at all

 *              possible.

 *

 * Returns:     NULL if the test succeeds.

 *              A non-zero result is the first address at which an

 *              aliasing problem was uncovered.  By examining the

 *              contents of memory, it may be possible to gather

 *              additional information about the problem.

 *

 **********************************************************************/

datum *

memTestAddressBus(volatile datum * baseAddress, unsigned long nBytes)

{

    unsigned long addressMask = (nBytes/sizeof(datum) - 1);

    unsigned long offset;

    unsigned long testOffset;

    datum pattern     = (datum) 0xAAAAAAAA;

    datum antipattern = (datum) 0x55555555;

    /*

     * Write the default pattern at each of the power-of-two offsets.

     */

    for (offset = 1; (offset & addressMask) != 0; offset <<= 1)

    {

        baseAddress[offset] = pattern;

    }

    /*

     * Check for address bits stuck high.

     */

    testOffset = 0;

    baseAddress[testOffset] = antipattern;

    for (offset = 1; (offset & addressMask) != 0; offset <<= 1)

    {

        if (baseAddress[offset] != pattern)

        {

            return ((datum *) &baseAddress[offset]);

        }

    }

    baseAddress[testOffset] = pattern;

    /*

     * Check for address bits stuck low or shorted.

     */

    for (testOffset = 1; (testOffset & addressMask) != 0; testOffset <<= 1)

    {

        baseAddress[testOffset] = antipattern;

                if (baseAddress[0] != pattern)

                {

                        return ((datum *) &baseAddress[testOffset]);

                }

        for (offset = 1; (offset & addressMask) != 0; offset <<= 1)

        {

            if ((baseAddress[offset] != pattern) && (offset != testOffset))

            {

                return ((datum *) &baseAddress[testOffset]);

            }

        }

        baseAddress[testOffset] = pattern;

    }

    return (NULL);

}   /* memTestAddressBus() */

/**********************************************************************

 *

 * Function:    memTestDevice()

 *

 * Description: Test the integrity of a physical memory device by

 *              performing an increment/decrement test over the

 *              entire region.  In the process every storage bit

 *              in the device is tested as a zero and a one.  The

 *              base address and the size of the region are

 *              selected by the caller.

 *

 * Notes:

 *

 * Returns:     NULL if the test succeeds.

 *

 *              A non-zero result is the first address at which an

 *              incorrect value was read back.  By examining the

 *              contents of memory, it may be possible to gather

 *              additional information about the problem.

 *

 **********************************************************************/

datum *

memTestDevice(volatile datum * baseAddress, unsigned long nBytes)

{

    unsigned long offset;

    unsigned long nWords = nBytes / sizeof(datum);

    datum pattern;

    datum antipattern;

    /*

     * Fill memory with a known pattern.

     */

    for (pattern = 1, offset = 0; offset < nWords; pattern++, offset++)

    {

        baseAddress[offset] = pattern;

    }

    /*

     * Check each location and invert it for the second pass.

     */

    for (pattern = 1, offset = 0; offset < nWords; pattern++, offset++)

    {

        if (baseAddress[offset] != pattern)

        {

            return ((datum *) &baseAddress[offset]);

        }

        antipattern = ~pattern;

        baseAddress[offset] = antipattern;

    }

    /*

     * Check each location for the inverted pattern and zero it.

     */

    for (pattern = 1, offset = 0; offset < nWords; pattern++, offset++)

    {

        antipattern = ~pattern;

        if (baseAddress[offset] != antipattern)

        {

            return ((datum *) &baseAddress[offset]);

        }

    }

    return (NULL);

}   /* memTestDevice() */