Table of Contents

Advertisement

Auxiliary
Storage
sets the condition code, and stores zeros in the addressed 4K-byte block and in
both keys if they are both unusable.
The two TEST BLOCK internal records are placed in auxiliary storage during IML.
These two records are maintained on functional diskette 1, which is shipped to a
4381 installation with all zeros in both records. During processor operation, any
time a double-bit error consisting of two solid errors or two consecutive protect key
errors occur, the TEST BLOCK internal record in auxiliary storage and that on
functional diskette 1 are updated. Thus, known unusable 4K-byte blocks are saved
across IMLs and power-offs. The TEST BLOCK internal records on functional
diskette 1 are updated as appropriate whenever processor storage is repaired.
The TB instruction is designed to be used during IPL to enable the operating
system to build a page frame table that indicates the known unusable 4K-byte page
frames to avoid their assignment. The TB should also be issued if an uncorrectable
storage error is encountered during system operation to attempt to validate the
unusable block (store good ECC bits). Successful validation will prevent the
occurrence of a machine check if the unusable block is prefetched or inadvertently
referenced.
The UCWs for System/370 mode or the subchannels and control unit blocks for
System/370-XA mode, the 1/0 queuing area, a trace area, the TEST BLOCK
internal records, and certain work areas are located in highest addressed processor
storage. This storage, called auxiliary storage, is reserved for processor rather than
program use and is inaccessible to all programs.
The size of auxiliary storage in bytes for a 4381 Processor Model Group 14
operating in System/370 mode is 90,120 (86,016 for the Model Group 3) plus 64
times the number of UCWs defined (128 to 2048) for each instruction processing
function rounded up to a 4K boundary. For System/370-XA mode, auxiliary
storage size in bytes for Model Groups 14 and 3 is 192,512 plus 70 times the
number of control units defined (1to256) plus 180 times the number of
subchannels defined (up to 2048) rounded up to a 4K boundary.
The minimum auxiliary storage requirement for System/370 mode of operation is
104Kb for the Model Group 14 (lOOKb for the Model Group 3) for 128 UCWs
defined for each instruction processing function, while the maximum requirement is
344Kb for the Model Group 14 (340Kb for the Model Group 3) for 2048 UCWs
defined for each instruction processing function. For System/370-XA mode of
operation, a minimum of 220Kb is required (for 128 subchannels and 128 control
unit control blocks) and the maximum requirement is 568Kb for 2048 subchannels
and 256 control unit control blocks.
The size of auxiliary storage is determined during IML. The processor storage
address of the first byte of auxiliary storage is calculated and placed in an address
check boundary (ACB) register. Any attempt to access an address equal to or
above the ACB register value during program execution results in an addressing
exception program interruption.
The contents of auxiliary storage vary depending on the mode, System/370 or
System/370-XA, in effect. During an IML, the required auxiliary storage area is
initialized as appropriate, using information contained on the functional diskette(s).
68
A Guide to the IBM 4381 Processor

Advertisement

Table of Contents
loading

Table of Contents