CCU/CSP Register Use
The CSP external registers are used by the following operations:
Program-initiated operation (PIO)
Adapter-initiated operation (AIO)
Interrupt operation.
Ping/Pong Buffers
Two half-word registers, called the ping and pong buffers, located in the local storage, are alternately
connected to the IOC bus in flip/flop mode.
They are used for transferring commands, data, and control words between the IOC bus and the CSP.
Switching from one buffer to the other is controlled by the IOC logic.
Processor Characteristics
Program Levels
The interrupts are raised by the microcode (all levels) or by hardware (levels 0, 1,
and 2). Levels 0 through 3 can be masked by the microcode.
Clock
An oscillator on the CSC card provides the 49.152 MHz square wave to generate the scanner
processor's clock. The 49.152 MHz is also sent to the FES and FESA for clock generation.
:
Two other
clocks are generated in the CSP:
A 100 ms clock used for timer purposes
A 15.4
µ
s clock used to refresh the storage.
Error Management
Internal CSP errors detected by the CSP hardware cause a CSP hardstop. Two bytes of status informa-
tion are presented by the CSP either to the CCU control program (NCP) or to the MOSS after the
hardstop condition is detected.
Hardstop
A hardstop condition is handled by the CSP hardware as follows:
1. A permanent cycle steal request is forced internally to the CSP processor, preventing any cycle steal
operation.
Cycle steal having the highest priority with CSP storage, the CSP microcode processing stops, but the
CSP clocks keep running.
A level 1 interrupt request is presented to the CCU control program (NCP) if the CSP is in
'Connect' mode.
Level
Function
0
Error handling and address compare
1
CCU instruction processing
2
FESL interrupt processing
3
Queue and command processing
4
Not used
5
Not used
6
Not used
7
Timer control and disconnect stop initialization
4-18
IBM 3745 Models 130, 150, 160, 170, and 17A: Hardware Maintenance Reference
Summary of Contents for 3745 Series
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