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Byte
Offset
Bits
Contents
CPU timer1
Clock comparator 1
,Program-status word
Time-of-day clock1
0-7
8-15
16-23
24-31
32-63
64-127
Floating-point registers 0, 2, 4, 6
General registers 0-15
128-191
192-199
200-203
204-207
208-211
212-215
216
0
1-3
4
5
6
7
217
0-3
218-219
220-255
4
5-7
Explanation:
Control registers 0-15
CPU I
D
1 .
Page-capacitycount 2
Existing-frame-capacity count 2
Available-frame-capacity count 2
Free-frame-capacity count 2
Zero
Page bits of page 0
Zero
Reference bit of page 0
Change bit of page 0
Zero
Access-control bits of page 0
Fetch-protection bit of page 0
Zeros
Frame index2 of page 0
Zeros
1
The formats of these fields are the same as
those produced by STORE CPU TIMER, STORE CLOCK
COMPARATOR, STORE CLOCK, and STORE CPU
10,
respectively.
2
The capacity counts and the frame index are
right~al
igned with leftmost bits of zeros.
Machine Status, Retrieval Format
previously saved information, the saved information
is indicated to be invalid, and subsequent execution
of RETRIEVE STATUS AND PAGE returns
condition code 3 until the next successful
machine-save operation. Invalid machine saves
cannot be retrieved.
The CPU must be in the stopped state before a
machine-save operation can be initiated.
If
an
error is encountered during the operation, the saved
information becomes invalid, the CPU enters the
check-stop state, and the save indicator is not
turned on.
Programming Notes
1. Machine save may be used as part of a
machine-dump procedure when the normal
supervisor program is not functioning properly,
such as after a hard wait (wait state with
interruptions disabled). By preserving the
complete machine status and page 0, machine
save permits loading a dump program, which
4-26
IBM 4300 Processors Principles of Operation
can preserve additional pages if necessary. The
dump program can then merge the saved
information with the undisturbed pages to
create a complete image of the machine at the
time of the machine save. The machine should
not be cleared before loading the dump
program.
2. When the supervisor program is still
functioning, it is less disruptive to use the
superVIsor to invoke a dump program without a
machine save. An intermediate option is the
restart function.
3. The format of the byte at offset 216
corresponds to the byte inserted by the
instruction INSERT PAGE BITS.
4. Unassigned bits in the retrieval format of the
machine status are stored as zeros. The
program should not depend on such zeros,
however, to ensure that existing programs run if
new facilities using these bits are defined.
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