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Help with EXCP

 
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steve-myers

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Joined: 30 Nov 2013
Posts: 585
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PostPosted: Sun Aug 27, 2017 5:45 am    Post subject: Help with EXCP
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I thought I understood EXCP pretty well, but this channel program is failing and I can't figure out what's going on.

The IOB is -
Code:
000178 42000000000002E8             120 IOB      DC    0XL40'0',AL1(X'42',0,0,0),A(ECB,0,0,CCWS,EXCP,0,0)
000198 0000000000000000             121 IOBSEEK  DC    XL8'0'


The channel program is -
Code:
0001A0 3100019B40000005             122 CCWS     CCW   X'31',IOBSEEK+3,X'40',5  SEARCH ID EQUAL
0001A8 080001A000000000             123          CCW   X'08',CCWS,0,0
0001B0 E90001C840000008             124          CCW   X'69'+X'80',KEY,X'40',8  SEARCH KEY HIGH EQUAL         ->
                                                                                 MULTI-TRACK
0001B8 080001B000000000             125          CCW   X'08',*-8,0,0
0001C0 060001E000000100             126          CCW   X'06',DIRBLOCK,0,L'DIRBLOCK  READ DATA


IOBSEEK does point to the first track of the data set. The R area is 0. IOBSEEK is filled in by using the CVTPCNVT routine with TTRN = X'00000000' rather than filling it in from DEB. This is all stuff I've done before.

The CSW in the IOB points to the TIC after the search key high-equal CCW.

The contents of KEY are CL8'ADDSTATS'

The contents of the actual key for the first record in the data set is BACKPDS.

The first byte of the ECB is X'41'.

I expect the search to end with first record and the contents of the first record to be read into storage.

As far as I can tell the CCW op codes are all correct.
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steve-myers

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Joined: 30 Nov 2013
Posts: 585
Location: The Universe

PostPosted: Mon Aug 28, 2017 10:33 am    Post subject:
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I've spent more time and I'm just as confused.

This is the IOB.
Code:
 IOB                                                                 00000000
        +0  46000000 4102DF5C 0002DE28 0C400008
            0102DE10 0002DF68 00000000 00000000
       +20  00000001 45000000

The 0C400008 the device status and the residual byte count. The 0C is channel end / device end. The 40 is wrong length! I'm thinking it's saying that R0 - the record in the search ID equal - does not have a key and that's why it's unhappy.

I'm going to start with R1.
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steve-myers

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PostPosted: Mon Aug 28, 2017 10:42 am    Post subject:
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That did it!

I switched to a data set with a multiple track search area and it seemed to work for the highest possible key.
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PeterHolland

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Location: Netherlands, Amstelveen

PostPosted: Wed Aug 30, 2017 12:35 pm    Post subject:
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Quote:
multiple track search area


And what is that?

The HA and R0 are written using special CCW commands when the volume is formatted. There is not normally any reason to read or write these special records. User data begins with Record One (R1) and may be followed by additional user records. An empty track contains only the HA and R0.
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steve-myers

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PostPosted: Wed Aug 30, 2017 5:16 pm    Post subject:
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You normally do a search for R0 to format write record R1, or to do a read count for R1, or to do a read multiple count-key-data for the track. As you say, ordinary programs seldom read the home address or R0. My track dump utility has an option to read and format HA and R0, but otherwise I leave them alone. It uses read multiple count-key-data to read the rest of the track. I use read count when doing a fast summary of a data set. My program to search out gas areas in a PDS uses long chains of read count multi-track commands; other than the directory it's not interested in the data.

I thought, incorrectly, that search key high equal would skip R0. Obviously it does in multi-track mode after switching tracks. The test program ran two searches, one for the first name, and one for the last name.

A PDS directory for a data set with many members typically extends over several tracks. For my test I used the PDS directory for SYS1.LINKLIB; in my system that's 14 tracks!
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