Chapter 5: C790 Processor Core
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
5-4
The C790 extends the normal MIPS-compatible register set by extending the width of the
general purpose registers (GPRs) from 64 bits to 128 bits. It also incorporates an additional
pair of HI/LO registers for the I1 pipe, and the SA register for funnel shift instructions.
5.3 C790
Registers
The C790 has 128-bit wide GPRs. The upper 64 bits of the GPRs are only used by the
C790-specific “Quad Load/Store”, and “Multimedia (Parallel)” instructions.
HI1 and LO1, which are the upper 64 bits of each of the 128-bit HI and LO registers, are
also used by new multiply and divide instructions such as MULT1, MULTU1, DIV1, DIVU1,
MADD1, MADDU1, MFHI1, MFLO1, MTHI1, and MTLO1, which are non-parallel I1 pipeline-
specific instructions. They are also used by multimedia (parallel) multiply and divide
instructions.
5.4 FPU
Registers
The floating-point unit (COP1) has thirty-two 64-bit wide floating-point registers. It also
contains two floating-point control registers.
5.5 Memory
Management
The C790 provides a memory management unit (MMU) which uses an on-chip translation
look-aside buffer (TLB) to translate virtual addresses into physical addresses.
Features
•
MIPS III-compatible 32-bit MMU
•
Operating Modes:
User, Supervisor, and Kernel
•
TLB:
48 entries of even/odd page pairs (96 pages)
Fully associative
•
Page Size:
4 KB, 16 KB, 64 KB, 256 KB, 1 MB, 4 MB, 16 MB
•
ITLB:
2
entries
•
DTLB:
4
entries
•
Address Sizes:
Virtual Address Size = 32 bits
Physical Address Size = 32 bits
5.6 Cache
Memory
The C790 contains an instruction cache and a separate data cache.
Features
•
Separate Instruction Cache and Data Cache
•
Caches are virtually indexed and physically tagged
•
Write-back policy for the Data Cache
•
Cache Size:
Instruction Cache:
32 KB
Data Cache:
32 KB
•
Line size:
64 Bytes
•
Associativity:
2-way
set-associative
•
Write Policy:
Write-back and write allocate
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