be purged under conditions additional to those for
which purging is mandatory.
States of Translation-Table Entries
The effects of any manipulation of the contents of a
table entry by the program and the recording of its
contents in the TLB depend on whether the entry is
valid, on whether the entry is attached, and on
whether the entry is active.
The valid state denotes that the segment or page
associated with the table entry is available. An entry
is valid when the segment-invalid bit or page-invalid
bit in the entry is zero. A segment-translation or
page-translation exception is recognized when an at
tempt is made to use an invalid table entry for trans
lation.
The attached state denotes that the CPU can
attempt to use the table entry for implicit address
translation and hence depends on the state of the
CPU as specified by the PSW, control register 1, and
bit positions 8-12 of control register o.
A segment-table entry is attached to a CPU when
all of the following three conditions are met:• The current PSW specifies the translation mode. • The entry is within the segment table designated
by control register 1.• With the segment size currently specified in
control register0, the entry can be designated
by a logical address.
The PSW is considered to specify the translation
mode when bit 5 is one and the EC mode is speci
fied, regardless of whether the contents of any other
PSW fields are due to cause an exception to be rec
ognized.
A page-table entry is attached to a CPU when it
is within the page table designated by the page-table
address and page-table length either in an attached
and valid segment-table entry or in a TLB copy of
an attached segment-table entry and by the page
size specification in control registerO. The active state denotes that the table entry may
remain recorded in the TLB.
A table entry becomes active when it is made
both valid and attached or after the TLB is purged
with the table entry both valid and attached. A table
entry ceases being active when the TLB is purged.
Although all entries become inactive during a purge
of the TLB, entries that are both valid and attached
become active at the completion of the purge. The segment size controls how many segment-table
entries can be referred to for translation. Both the
page size and segment size control selection of page-
Page ofGA22-7000-4 Revised September 1, 1975
By TNL: GN22-0498
table entries and hence may affect whether or not an
entry is attached.
Although a table entry becomes active when it is
made both valid and attached, it need not remain
valid and attached to remain active. For example, an
attached table entry remains active when the I bit is
set to one, and a valid table entry remains active
when it is made unattached.
Use of the Translation-Lookaside Buffer
A segment-table entry or a page-table entry may be
placed in the TLB only when the entry is attached
and the I bit in the entry is zero. The entry may be
placed in the TLB as soon as it becomes attached
and valid.
Information from a TLB copy of a segment-table
entry may be used for implicit address translation
only when the TLB entry was formed using informa
tion that was fetched from storage as an attached
and valid segment-table entry, only when that real
storage location is selected as a segment-table entry
during the translation process, and only when the
table entry is attached at the time of the selection.
Information from a TLB copy of a page-table
entry may be used for implicit address translation
only when the TLB entry was formed using informa
tion that was fetched from storage as an attached
and valid page-table entry, only when that real stor
age location is selected as a page-table entry during
the translation process and the table entry is attached
at the time of selection, and only when the
page size at the time of forming the TLB copy was
the same as the current page size.
The operand address ofLOAD REAL AD
DRESS is translated without the use of the TLB
contents. Translation in this case is performed by the
use of the designated tables in main storage.
All information in the TLB is necessarily cleared
only by execution of PURGE TLB, SET PREFIX,
or CPU reset.
Programming No entries can be placed in the TLB in the BC mode
or when translation is not specified, because the
table entries at this time are not attached. In particu
lar, translation of the operand address ofLOAD REAL ADDRESS, with translation suppressed, does
not cause entries to be placed in the TLB.
Conversely, when translation is specified, infor
mation may be loaded into the TLB from all
translation-table entries that could be used for ad
dress translation, given the current designation of
page size, segment size, segment-table address, and
segment-table length. The loading of the TLB does
not depend on whether the entry is used for transla-
Dynamic Address Translation65
which purging is mandatory.
States of Translation-Table Entries
The effects of any manipulation of the contents of a
table entry by the program and the recording of its
contents in the TLB depend on whether the entry is
valid, on whether the entry is attached, and on
whether the entry is active.
The valid state denotes that the segment or page
associated with the table entry is available. An entry
is valid when the segment-invalid bit or page-invalid
bit in the entry is zero. A segment-translation or
page-translation exception is recognized when an at
tempt is made to use an invalid table entry for trans
lation.
The attached state denotes that the CPU can
attempt to use the table entry for implicit address
translation and hence depends on the state of the
CPU as specified by the PSW, control register 1, and
bit positions 8-12 of control register o.
A segment-table entry is attached to a CPU when
all of the following three conditions are met:
by control register 1.
control register
by a logical address.
The PSW is considered to specify the translation
mode when bit 5 is one and the EC mode is speci
fied, regardless of whether the contents of any other
PSW fields are due to cause an exception to be rec
ognized.
A page-table entry is attached to a CPU when it
is within the page table designated by the page-table
address and page-table length either in an attached
and valid segment-table entry or in a TLB copy of
an attached segment-table entry and by the page
size specification in control register
remain recorded in the TLB.
A table entry becomes active when it is made
both valid and attached or after the TLB is purged
with the table entry both valid and attached. A table
entry ceases being active when the TLB is purged.
Although all entries become inactive during a purge
of the TLB, entries that are both valid and attached
become active at the completion of the purge.
entries can be referred to for translation. Both the
page size and segment size control selection of page-
Page of
By TNL: GN22-0498
table entries and hence may affect whether or not an
entry is attached.
Although a table entry becomes active when it is
made both valid and attached, it need not remain
valid and attached to remain active. For example, an
attached table entry remains active when the I bit is
set to one, and a valid table entry remains active
when it is made unattached.
Use of the Translation-Lookaside Buffer
A segment-table entry or a page-table entry may be
placed in the TLB only when the entry is attached
and the I bit in the entry is zero. The entry may be
placed in the TLB as soon as it becomes attached
and valid.
Information from a TLB copy of a segment-table
entry may be used for implicit address translation
only when the TLB entry was formed using informa
tion that was fetched from storage as an attached
and valid segment-table entry, only when that real
storage location is selected as a segment-table entry
during the translation process, and only when the
table entry is attached at the time of the selection.
Information from a TLB copy of a page-table
entry may be used for implicit address translation
only when the TLB entry was formed using informa
tion that was fetched from storage as an attached
and valid page-table entry, only when that real stor
age location is selected as a page-table entry during
the translation process and the table entry is attached
at the time of selection, and only when the
page size at the time of forming the TLB copy was
the same as the current page size.
The operand address of
DRESS is translated without the use of the TLB
contents. Translation in this case is performed by the
use of the designated tables in main storage.
All information in the TLB is necessarily cleared
only by execution of PURGE TLB, SET PREFIX,
or CPU reset.
Programming
or when translation is not specified, because the
table entries at this time are not attached. In particu
lar, translation of the operand address of
not cause entries to be placed in the TLB.
Conversely, when translation is specified, infor
mation may be loaded into the TLB from all
translation-table entries that could be used for ad
dress translation, given the current designation of
page size, segment size, segment-table address, and
segment-table length. The loading of the TLB does
not depend on whether the entry is used for transla-
Dynamic Address Translation