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/* xmsa20.c - A20 related XMS routines
*
* XMSA20
*
* Modification History:
*
* Sudeepb 15-May-1991 Created
*/
#include "xms.h"
#include <xmssvc.h>
#include <softpc.h>
void sas_enable_20_bit_wrapping(void);
void sas_disable_20_bit_wrapping(void);
BOOL sas_twenty_bit_wrapping_enabled(void);
BYTE * pHimemA20State = NULL;
/* xmsA20 - Handle A20 requests
*
*
* Entry - Client (AX) 0 - Disable A20
* 1 - Enable A20
* 2 - Query
*
* Exit
* SUCCESS
* Client (AX) = 1
* if on entry AX=2 Then
* Cleint (AX) =1 means was enabled
* Cleint (AX) =0 means was disabled
*
* FAILURE
* Client (AX) = 0
*/
VOID xmsA20 (VOID)
{
int reason;
reason = getAX();
setAX(1);
if (reason == 0)
xmsEnableA20Wrapping();
else if (reason == 1)
xmsDisableA20Wrapping();
else if (reason == 2) {
if (sas_twenty_bit_wrapping_enabled())
setAX(0);
setBL(0);
}
else
setAX(0);
}
// function to enable 1MB wrapping (turn off A20 line)
VOID xmsEnableA20Wrapping(VOID)
{
sas_enable_20_bit_wrapping();
if (pHimemA20State != NULL)
*pHimemA20State = 0;
#if 0 // this is not necessay because the intel space(pointed by
// HimemA20State) doesn't contain instruction
// doesn't contain instruction
#ifdef MIPS
Sim32FlushVDMPointer
(
(((ULONG)pHimemA20State >> 4) << 16) | ((ULONG)pHimemA20State & 0xF),
1,
pHimemA20State,
FALSE
);
#endif
#endif
}
// function to disable 1MB wrapping(turn on A20 line)
VOID xmsDisableA20Wrapping(VOID)
{
sas_disable_20_bit_wrapping();
if (pHimemA20State != NULL)
*pHimemA20State = 1;
#if 0 // this is not necessay because the intel space(pointed by
// HimemA20State) doesn't contain instruction
// doesn't contain instruction
#ifdef MIPS
Sim32FlushVDMPointer
(
(((ULONG)pHimemA20State >> 4) << 16) | ((ULONG)pHimemA20State & 0xF),
1,
pHimemA20State,
FALSE
);
#endif
#endif
}
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