PIC32MX1XX Datasheet, PDF (34/320 Pages) Microchip Technology – 32-bit Microcontrollers (up to 128 KB Flash and 32 KB SRAM) with Audio and Graphics Interfaces, USB, and Advanced Analog

PIC32MX1XX/2XX
3.2 Architecture Overview
The MIPS32^® M4K^® processor core contains several
logic blocks working together in parallel, providing an
efficient high-performance computing engine. The
following blocks are included with the core:
• Execution Unit
• Multiply/Divide Unit (MDU)
• System Control Coprocessor (CP0)
• Fixed Mapping Translation (FMT)
• Dual Internal Bus interfaces
• Power Management
• MIPS16e Support
• Enhanced JTAG (EJTAG) Controller
3.2.1 EXECUTION UNIT
The MIPS32^® M4K^® processor core execution unit
implements a load/store architecture with single-cycle
ALU operations (logical, shift, add, subtract) and an
autonomous multiply/divide unit. The core contains
thirty-two 32-bit General Purpose Registers (GPRs)
used for integer operations and address calculation.
One additional register file shadow set (containing
thirty-two registers) is added to minimize context
switching overhead during interrupt/exception process-
ing. The register file consists of two read ports and one
write port and is fully bypassed to minimize operation
latency in the pipeline.
The execution unit includes:
• 32-bit adder used for calculating the data address
• Address unit for calculating the next instruction
address
• Logic for branch determination and branch target
address calculation
• Load aligner
• Bypass multiplexers used to avoid stalls when
executing instruction streams where data
producing instructions are followed closely by
consumers of their results
• Leading Zero/One detect unit for implementing
the CLZ and CLO instructions
• Arithmetic Logic Unit (ALU) for performing bitwise
logical operations
• Shifter and store aligner
3.2.2 MULTIPLY/DIVIDE UNIT (MDU)
The MIPS32^® M4K^® processor core includes a Multi-
ply/Divide Unit (MDU) that contains a separate pipeline
for multiply and divide operations. This pipeline oper-
ates in parallel with the Integer Unit (IU) pipeline and
does not stall when the IU pipeline stalls. This allows
MDU operations to be partially masked by system stalls
and/or other integer unit instructions.
The high-performance MDU consists of a 32x16 booth
recoded multiplier, result/accumulation registers (HI
and LO), a divide state machine, and the necessary
multiplexers and control logic. The first number shown
(‘32’ of 32x16) represents the rs operand. The second
number (‘16’ of 32x16) represents the rt operand. The
PIC32 core only checks the value of the latter (rt) oper-
and to determine how many times the operation must
pass through the multiplier. The 16x16 and 32x16
operations pass through the multiplier once. A 32x32
operation passes through the multiplier twice.
The MDU supports execution of one 16x16 or 32x16
multiply operation every clock cycle; 32x32 multiply
operations can be issued every other clock cycle.
Appropriate interlocks are implemented to stall the
issuance of back-to-back 32x32 multiply operations.
The multiply operand size is automatically determined
by logic built into the MDU.
Divide operations are implemented with a simple 1 bit
per clock iterative algorithm. An early-in detection
checks the sign extension of the dividend (rs) operand.
If rs is 8 bits wide, 23 iterations are skipped. For a 16-bit
wide rs, 15 iterations are skipped and for a 24-bit wide
rs, 7 iterations are skipped. Any attempt to issue a sub-
sequent MDU instruction while a divide is still active
causes an IU pipeline stall until the divide operation is
completed.
Table 3-1 lists the repeat rate (peak issue rate of cycles
until the operation can be reissued) and latency (num-
ber of cycles until a result is available) for the PIC32
core multiply and divide instructions. The approximate
latency and repeat rates are listed in terms of pipeline
clocks.
TABLE 3-1:
MIPS32^® M4K^® PROCESSOR CORE HIGH-PERFORMANCE INTEGER
MULTIPLY/DIVIDE UNIT LATENCIES AND REPEAT RATES
Opcode
Operand Size (mul rt) (div rs)
Latency
Repeat Rate
MULT/MULTU, MADD/MADDU,
MSUB/MSUBU
MUL
DIV/DIVU
16 bits
32 bits
16 bits
32 bits
8 bits
16 bits
24 bits
32 bits
1
1
2
2
2
1
3
2
12
11
19
18
26
25
33
32
DS61168D-page 34
Preliminary
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