AT&T 3B2/300 Technical Reference Manual page 352

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ID Number Cache.
The ID Number Cache (IDNC) is used to transparently assign ID numbers to
each section of the MMU. The cache is organized in a 16-entry, fully associative configuration. Each
entry is 32 bits in length divided into "tag" bits and data bits.
Current ID Number Registers. The Current ID Number Registers (CIDNR) contain the four current
ID numbers (consisting of 4 bits each). The CIDNR is used during translation to select the ID number
to be used in the page descriptor cache tag lookup.
Segment Descriptor Cache. The Segment Descriptor Cache (SOC) consists of eight entries in a
directly mapped configuration. Each entry is 64 bits in length.
Page Descriptor Cache.
The Page Descriptor Cache (PDC) consists of sixty-four 64-bit entries
organized in a fully associative configuration.
Section Random Access Memories.
The MMU contains two Random Access Memory (RAM)
areas called Section RAM A (SRAMA) and Section RAM B (SRAMB). Each of these areas contain four
32-bit words. SRAMA bits 31-03 describes the base address of the Segment Descriptor Table (SOT)
for each of the four sections of virtual memory. SRAMB bits 22-10 describes the length (number of
entries) in the SOT for each of the four sections of virtual memory. The contents of SRAMA (4 words)
and SRAMB (4 words) are part of the error report output by the
/etc/errdump command. The SRAMA
and SRAMB are identified as "srama" and "sramb" in the error report. The format of SRAMA and
SRAMB are as follows.
SECTION RAM A (SRAMA)
BITS 31-03 02-00
FIELD SOT ADDRESS RESERVED
SECTION RAM B (SRAMB)
BITS
31 - 23 22 - 10 09 - 00
FIELD RESERVED SOT LENGTH
RESERVED
MMU Registers.
The MMU contains five 32-bit registers:
• Fault Code Register (FL TCR)
• Fault Address Register (FLT AR)
• Virtual Address Register (VAR)
• Configuration Register (CR)
• Flush ID Number Register (FIDNR).
These registers are used to store MMU state information. The contents of FLTAR and FLTCR are
part of the error report output by the
/etc/errdump command. The FLTAR and FLTCR are identified
as "fltar" and "fltcr" in the error report.
FUNCTIONAL DESCRIPTION 3-99