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Multiply-Accumulate Unit (MAC)
MCF5213 ColdFire® Integrated Microcontroller Reference Manual, Rev. 3
Freescale Semiconductor
4-3
Because the multiplier array is implemented in a three-stage pipeline, MAC instructions have an effective
issue rate of 1 cycle for word operations, 3 cycles for longword integer operations, and 4 cycles for 32-bit
fractional operations.
All arithmetic operations use register-based input operands, and summed values are stored in the
accumulator. Therefore, an additional MOVE instruction is needed to store data in a general-purpose
register.
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 efficiently move large data blocks by generating line-sized burst references. The ability to
load an operand simultaneously 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 mask register (MASK), which can optionally be used to generate an
operand address during MAC + MOVE instructions. The register application with auto-increment
addressing mode supports efficient implementation of circular data queues for memory operands.
4.4
Memory Map/Register Definition
The following table and sections explain the MAC registers:
4.4.1
MAC Status Register (MACSR)
The MAC status register (MACSR) contains a 4-bit operational mode field and condition flags.
Operational mode bits control whether operands are signed or unsigned and whether they are treated as
integers or fractions. These bits also control the overflow/saturation mode and the way in which rounding
is performed. Negative, zero, and overflow condition flags are also provided.
Table 4-1. MAC Memory Map
Register
Width
(bits)
Access
Reset Value
Section/Page
0x804
MAC Status Register (MACSR)
32
R/W
0x0000_0000
0x805
MAC Address Mask Register (MASK)
32
R/W
0xFFFF_FFFF
0x806
Accumulator (ACC)
32
R/W
Undefined
1
The values listed in this column represent the Rc field used when accessing the core registers via the BDM port. For more
information see
BDM: 0x804 (MACSR)
Access: Supervisor read/write
BDM read/write
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
0
R 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
OMC S/U
F/I
R/T
C
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0
0
0
0
0
0
0
0
Figure 4-2. MAC Status Register (MACSR)
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