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77 lines
2.3 KiB
77 lines
2.3 KiB
// $Header: G:/SwDev/WDM/Video/bt848/rcs/Regfield.cpp 1.3 1998/04/29 22:43:36 tomz Exp $
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#include "regfield.h"
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/* Method: RegField::MakeAMask
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* Purpose: Computes a mask used to isolate a field withing a register based
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* on the width of a field
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*/
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inline DWORD RegField::MakeAMask()
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{
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// compute the mask to apply to the owner register to reset
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// all bits that are part of a field. Mask is based on the size of a field
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return ::MakeAMask( FieldWidth_ );
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}
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/* Method: RegField::operator DWORD()
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* Purpose: Performs the read from a field of register
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*/
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RegField::operator DWORD()
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{
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// if write-only, get the shadow
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if ( GetRegisterType() == WO )
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return GetShadow();
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// for RO and RW do the actual read
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// get the register data and move it to the right position
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DWORD dwValue = ( Owner_ >> StartBit_ );
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DWORD dwMask = MakeAMask();
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return dwValue & dwMask;
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}
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/* Method: RegField::operator=
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* Purpose: performs the assignment to a field of register
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* Note:
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This function computes the mask to apply to the owner register to reset
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all bits that are part of a field. Mask is based on the start position and size
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Then it calculates the proper value from the passed argument ( moves the size
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number of bits to the starting position ) and ORs these bits in the owner register.
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*/
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DWORD RegField::operator=( DWORD dwValue )
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{
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// if a register is read-only nothing is done. This is an error
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if ( GetRegisterType() == RO )
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return ReturnAllFs();
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SetShadow( dwValue );
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// get a mask
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DWORD dwMask = MakeAMask();
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// move mask to a proper position
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dwMask = dwMask << StartBit_;
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// calculate the proper value from the passed argument ( move the size
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// number of bits to the starting position )
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DWORD dwFieldValue = dwValue << StartBit_;
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dwFieldValue &= dwMask;
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// do not perform intermediate steps on the owner; rather use a temp and update
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// the owner at once
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DWORD dwRegContent = Owner_;
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// reset the relevant bits
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if ( GetRegisterType() == RR )
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dwRegContent = 0;
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else
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dwRegContent &= ~dwMask;
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// OR these bits in the owner register.
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dwRegContent |= dwFieldValue;
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Owner_ = dwRegContent;
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return dwValue;
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}
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