Memory Write Protection Locks; Llocks; Llockse - Xerox 550 Reference Manual

The instruction format for loading the access protection
code is:
Depending upon the type of addressing, the format of reg-
ister R contents is one of the following:
IfMA=O;
If MA
=
1 and MM
=
0;
For eithertype of addressing, the contents of register Ru 1 are:
ACCESS PROTECTION LOADING PROCESS
The initial access protection control image address in reg-
ister R is the virtual address of the first word of the access
protection control image.
The initial count in register Ru1 specifies the word length of
~he c~!"!~:-d
!m!:!ge
t~
be !0!:!clecl ,A """rd
~ount
of 16 ic; c;uf-
fi cient to load the entire block of 256 access protection con-
trol registers. The access protection control registers are
treated as a circular set, with the first register fol lowing the
last; thus, a word count greater than 16 causes the first reg-
isters loaded to be overwritten.
The initial value of the control start field of register Ru 1
points to the first page (512 words) of virtual addresses that
are to be controlled by the access protection control image
being loaded. The access protection control image is loaded
into the access control registers one word at a time, thus
loading the control registers for 16 consecutive pages with the
contents of each image word. As each image word is loaded,
the access protection control image address is incremented
by 1, the word count is decremented by 1, and the value in
the control start field is incremented by
4.
The loading
process continues until the word count is reduced to
O.
When the loading process is completed, the parameters con-
tained within registers Rand Ru1 have the following values!
Access protection
control image address
=
initial access protection control
image address plus the initial word
count.
Count
=
O.
Control Start
=
initial contents plus 4 times the
initial word count.
MEMORY WRITE PROTECTION LOCKS
CONTROL IMAGE
Each write lock control image word may contain either
eight 4-bit write lock images or sixteen 2-bit write lock
images, as illustrated below:
Typical write locks image word (4-bit format);
Typical write locks image word (2-bit format);
The number of words required to define the memory write
locks control image is dependent upon the format of the
write lock images and the number of write lock registers to
be loaded by a single MMC instruction. (For example, if
the write lock images are of the 4-bit format and the memory
system is maximum size (1,024,000 words or 2048 pages)
with 2048 write lock control registers, the control image
may be defined by 256 words (i. e., 256 words times 8 write
lock images per word is equal to 2048 write lock images or
one write lock image per each write lock control register).
If the write lock images are of the 2-bit format and the
memory size is the same, as described above, the control
image may be defined by 128 words.
The instruction format for loading 2-bit write lock images is:
LLOCKS LOAD LOC KS (2-bit format)
The instruction format for loading 4-bit write lock images is:
LLOCKSE
LOAD LOC KS (4-bit format)
If MA
=
0, the contents of register Rare:
lock
lmag~
Address
If MA
=
1 and MM
=
0, the contents of register Rare:
Control Instructions 99