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ColdFire CF4e Core User’s Manual
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Memory Map/Register Set
The need to move large amounts of data presents an obstacle to obtaining high throughput
rates in DSP engines. New and existing ColdFire instructions can accommodate these
requirements. A MOVEM instruction can move large blocks of data efficiently by
generating line-sized burst references. The ability to simultaneously load an operand from
memory into a register and execute a MAC instruction makes some DSP operations such
as filtering and convolution more manageable.
The programming model includes a 16-bit mask register (MASK), which can optionally be
used to generate an operand address during MAC + MOVE instructions. The application of
this register with auto-increment addressing mode supports efficient implementation of
circular data queues for memory operands.
The additional MACSR contains a 4-bit operational mode field and condition flags.
Operational mode bits control the overflow/saturation mode, whether operands are signed
or unsigned, whether operands are treated as integers or fractions, and how rounding is
performed. Negative, zero, and multiple overflow condition flags are also provided.
5.4 Memory Map/Register Set
The EMAC provides the following program-visible registers:
Four 32-bit accumulators (ACCx = ACC0, ACC1, ACC2, and ACC3)
Eight 8-bit accumulator extensions (two per accumulator), packaged as two 32-bit
values for load and store operations (ACCext01 and ACCext23)
One 16-bit mask register (MASK)
One 32-bit MAC status register (MACSR) including four indicator bits signaling
product or accumulation overflow (one for each accumulator: PAV0–PAV3)
These registers are shown in Figure 5-6.
Figure 5-6. EMAC Register Set
5.4.1 MAC Status Register (MACSR)
MACSR functionality is organized as follows:
MACSR[11–8] contains one product/accumulation overflow flag per accumulator.
MACSR[7–4] defines the operating configuration of the MAC unit.
31
0
MACSR
ACC0
ACC1
ACC2
ACC3
ACCext01
ACCext23
MASK
MAC status register
MAC accumulator 0
MAC accumulator 1
MAC accumulator 2
MAC accumulator 3
Extensions for ACC0 and ACC1
Extensions for ACC2 and ACC3
MAC mask register
F
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