PIC32MX575F256H-80I Datasheet, PDF (40/236 Pages) Microchip Technology – High-Performance, USB, CAN and Ethernet 32-Bit Flash Microcontrollers

PIC32MX5XX/6XX/7XX
3.2 Architecture Overview
The PIC32MX5XX/6XX/7XX family core contains sev-
eral 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 PIC32MX5XX/6XX/7XX family 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 PIC32MX5XX/6XX/7XX family core includes a
Multiply/Divide Unit (MDU) that contains a separate
pipeline for multiply and divide operations. This pipeline
operates 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
PIC32MX core only checks the value of the latter (rt)
operand 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 PIC32MX
core multiply and divide instructions. The approximate
latency and repeat rates are listed in terms of pipeline
clocks.
DS61156C-page 40
Preliminary
 2010 Microchip Technology Inc.