Section 3 Memory Management Unit (MMU)
Rev. 5.00 May 29, 2006 page 80 of 698
REJ09B0146-0500
3.7.2
Use of TLB
An erroneous value is set in the RC bit in MMUCR when all of the following conditions are
satisfied.
1. MMU is on (AT bit in MMUCR is 1)
2. Same VPN exists in more than one ways in a single entry in a TLB address array
3. TLB exception is generated
VPN is not initialized by a power-on reset or a manual reset. Therefore, two or more VPNs have
the same values in a single entry. When an entry in this state is registered to way 3, for example,
the state of that entry in the TLB address array becomes as shown below. As a result, the same
VPN exists in both way 0 and way 3, and condition 2 above is satisfied.
After reset
After registered to way 3
WAY
VPN
V
WAY
VPN
V
0
12345
0
0
12345
0
3
12345
0
3
12345
1
A condition may also be satisfied when the TLB is handled by software. For example, if an entry
in the TLB address array is registered to way 3 after way 0 is disabled (V bit is changed from 1 to
0), the state of that entry becomes as shown below. Similar to the above case, the same VPN exists
in both way 0 and way 3, and condition 2 above is satisfied.
After way 0 is disabled
After registered to way 3
WAY
VPN
V
WAY
VPN
V
0
12345
0
0
12345
0
3
11111
0
3
12345
1
To avoid this failure, take the following two countermeasures.
1. After a reset, initialize the upper four bits in VPN to 1 for all entries in the TLB address array
until the AT bit in MMUCR is set to 1.
2. When disabling a way in the TLB address array, in addition to clearing the V bit to 0, initialize
the upper four bits in VPN to 1.
These countermeasures will prevent VPN from being a target of address translation. Accordingly,
condition 3 is not satisfied, and this failure can be avoided.
Summary of Contents for SH7706 Series
Page 8: ...Rev 5 00 May 29 2006 page viii of xlviii ...
Page 160: ...Section 5 Cache Rev 5 00 May 29 2006 page 112 of 698 REJ09B0146 0500 ...
Page 370: ...Section 11 Watchdog Timer WDT Rev 5 00 May 29 2006 page 322 of 698 REJ09B0146 0500 ...
Page 554: ...Section 17 Pin Function Controller PFC Rev 5 00 May 29 2006 page 506 of 698 REJ09B0146 0500 ...
Page 576: ...Section 18 I O Ports Rev 5 00 May 29 2006 page 528 of 698 REJ09B0146 0500 ...
Page 746: ...Index Rev 5 00 May 29 2006 page 698 of 698 REJ09B0146 0500 ...
Page 749: ...SH7706 Group Hardware Manual ...