Freescale Semiconductor MCF5480 - Manual (Page 157)

Memory Map/Register Definition
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 4-9
then Result = R0.U + 1
else if lsb of R0.U = 0
/* R0.L = 0x8000 */
then Result = R0.U
else Result = R0.U + 1
The round-to-nearest-even technique is also known as convergent rounding.
4.2.1.1.2 Saving and Restoring the EMAC Programming Model
The presence of rounding logic in the output datapath of the EMAC requires that special care be taken
during the EMAC’s save/restore process. In particular, any result rounding modes must be disabled during
the save/restore process so the exact bit-wise contents of the EMAC registers are accessed. Consider the
following memory structure containing the EMAC programming model:
struct macState {
int acc0;
int acc1;
int acc2;
int acc3;
int accext01;
int accext02;
int mask;
int macsr;
} macState;
The following assembly language routine shows the proper sequence for a correct EMAC state save. This
code assumes all Dn and An registers are available for use and the memory location of the state save is
defined by A7.
EMAC_state_save:
move.l macsr,d7 ; save the macsr
clr.l d0 ; zero the register to ...
move.l d0,macsr ; disable rounding in the macsr
move.l acc0,d0 ; save the accumulators
move.l acc1,d1
move.l acc2,d2
move.l acc3,d3
move.l accext01,d4
; save the accumulator extensions
move.l accext23,d5
move.l mask,d6
; save the address mask
movem.l #0x00ff,(a7) ; move the state to memory
The following code performs the EMAC state restore:
EMAC_state_restore:
movem.l (a7),#0x00ff ; restore the state from memory
move.l #0,macsr ; disable rounding in the macsr
move.l d0,acc0 ; restore the accumulators
move.l d1,acc1
move.l d2,acc2
move.l d3,acc3
move.l d4,accext01
; restore the accumulator extensions
move.l d5,accext23