UM0434 datasheet(195/390 Pages) STMICROELECTRONICS

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Memory management unit

UM0434

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7.2.4

Translation flow

The effective address, concatenated with the address space value of the corresponding

MSR bit (MSR[IS] or MSR[DS]), is compared to the appropriate number of bits of the EPN

field (depending on the page size) and the TS field of TLB entries. If the contents of the

effective address plus the address space bit matches the EPN field and TS bit of the TLB

entry, that TLB entry is a candidate for a possible translation match. In addition to a match in

the EPN field and TS, a matching TLB entry must match with the current process ID of the

access (in PID0), or have a TID value of 0, indicating that the entry is globally shared among

all processes.

Figure 8 shows the translation match logic for the effective address plus its attributes,

collectively called the virtual address, and how it is compared with the corresponding fields

in the TLB entries.

Figure 8.

Virtual address and TLB-Entry compare process

The page size defined for a TLB entry determines how many bits of the effective address

are compared with the corresponding EPN field in the TLB entry as shown in

Table 151. On

a TLB hit, the corresponding bits of the real page number (RPN) field are used to form the

real address, and the generation of the physical address occurs as shown in

Figure 7.

Table 151.

Page size (for e200z3 Core) and EPN field comparison

SIZE Field

Page Size

(4SIZE Kbytes)

EA to EPN Comparison

(Bits 32–53; 2

× SIZE)

0b0001

4 Kbytes

EA[32–51] = EPN[32–51]?

0b0010

16 Kbytes

EA[32–49] = EPN[0–49]?

0b0011

64 Kbytes

EA[32–47] = EPN[32–47]?

0b0100

256 Kbytes

EA[32–45] = EPN[32–45]?

0b0101

1 Mbyte

EA[32–43] = EPN[32–43]?

0b0110

4 Mbytes

EA[32–41] = EPN[32–41]?

0b0111

16 Mbytes

EA[32–39] = EPN[32–39]?

0b1000

64 Mbytes

EA[32–37] = EPN[32–37]?

0b1001

256 Mbytes

EA[32–35] = EPN[32–35]?

TLB Entry Hit

=0?

Private Page

Shared Page

TLB_entry[V]

TLB_entry[TS]

TLB_entry[TID]

TLB_entry[EPN]

AS (from MSR[IS] or MSR[DS])

Process ID

EA Page Number Bits

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