Browse Prior Art Database

Host I/O Data Management Enhanced by Unique CCW Coding

IP.com Disclosure Number: IPCOM000089124D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 15K

Publishing Venue

IBM

Related People

Opdahl, RC: AUTHOR

Abstract

As an alternative to giving a Front End Processor (FEP) direct physical access to a host computer's memory, a channel-to-channel (CTC) adapter can be used as the link between the FEP and Host Memory. To relieve the host of most of the usual Channel Control Word (CCW) generation, and execution of numerous Start I/O (SIO) instructions and interrupts associated with CTC programming, a unique communication method is employed. Host I/O operations with the CTC adapter are limited to the following three items: 1) Attention interrupt handler to read the command byte from the FEP side of the CTC adapter; 2) SIO to a fixed CCW string; and 3) Ending Interrupt Handler to post all current input/output data transfers between Host Memory and the FEP as being completed.

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Host I/O Data Management Enhanced by Unique CCW Coding

As an alternative to giving a Front End Processor (FEP) direct physical access to a host computer's memory, a channel-to-channel (CTC) adapter can be used as the link between the FEP and Host Memory. To relieve the host of most of the usual Channel Control Word (CCW) generation, and execution of numerous Start I/O (SIO) instructions and interrupts associated with CTC programming, a unique communication method is employed. Host I/O operations with the CTC adapter are limited to the following three items: 1) Attention interrupt handler to read the command byte

from the FEP side of the CTC adapter;

2) SIO to a fixed CCW string; and

3) Ending Interrupt Handler to post all current input/output

data transfers between Host Memory and the FEP as being

completed.

For example, assuming data transfer from FEP to Host Memory, the following CCW operations will execute in the Host and in the FEP. Command Chained (CC) and Transfer in Channel (TIC) commands are used. HOST -OR- FEP

ATTENTION ATTENTION (caused by SIO WRT in FEP) (caused by SIO RD in Host)

SIO SIO CCW1 RD into CCW2, CC ...... CCW1 WRT (CCW2 in Host)

CCW2 (from FEP) ............ CCW2 (RD/WRT to match CCW2 in Host)
CCW3 TIC to CCW1 ........... CCW3 No-Op/TIC to CCW1 (The FEP chain is broken if No-Op

is executed, and must be restarted

at CCW1. The Host CCW string is

suspended when the FEP chain is

broken, and continues after the FEP

chain is restarted without

requiring a SIO at the Host.)

The sequence of events is as follows:
1. Either CPU can initiate the transfer by issuing a SIO to its first CCW. That causes an Attention interrupt in the other CPU, which then issues a SIO to its CCW1.

Assume that the Host CPU initiated the action. Then: (a) The Host issues a SIO to its CCW1 (a Read command).

(b) The FEP sees an Attention interrupt.

(c) The FEP issues a SIO to its CCW1 (a Write CCW).
2. Data flows from the FEP.

The origin is specified by the FEP CCW1 data address. The destination is specified by the Host CCW1 data address.
3. The data read into the Host is placed into CCW2 and is therefore the actual Host CCW2.
4. When the data is transferred and no error occurs, then CCW2 in

1

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the Host and FEP both are executed. Note that the Host CCW2 was sent from the FEP to the Host.
5. Data flows from the FEP to the Host.

The origin is the data address of the FEP Write CCW2. The destination is the data address of the Host Read CMW2 (which was generated in the FEP).

This data flow is the "real" data, e.g., information generated in the FEP and moved into Host memory at an address specified by the FEP.
6. CCW2 completes in both Host and FEP. Both channels proceed to execute CFW3.

In the Host, CCW3 merely transfers control to CCW1 which transfers no data until it is complemented by the FEP CCW1.

In the FEP, CCW3 is executed. If programming had been fast enough, it would have changed the No-Op CCW to a TIC to CCW1. If not, then the No-...