Now we are ready to start preparing to IPL directly from a DASD volume instead of the card reader. \u00a0When the CPU IPL’s from DASD the IPL record at CC=0000 HH=00000 R=01 will be read into memory. \u00a0Just like our first IPL card it contains a PSW and two CCW’s. \u00a0The first CCW is a Read Data (X’06’). Since it is chained from the initial IPL CCW we do not need a Seek or Search CCW. \u00a0The Read CCW will read the next record on the track (CC=0000 HH=0000 R=02). \u00a0This second IPL record contains\u00a0additional CCW’s and data.<\/p>\n
The first IPL record has a Key Length of 4 with the value ‘IPL1’ and a Data Length of 24. \u00a0The second IPL record has a Key Length of 4 with a value of ‘IPL2′ \u00a0and a Data Length of 144 (or at least it does on my 3350). \u00a0These records were created when the volume was initialized.<\/p>\n
The third record is the Volume Label and is followed by the IPL text in record 4.<\/p>\n
Our IPL1 record needs to contain a PSW and two CCW’s. \u00a0We will load the contents of the second record at location x’4000’ so our first record needs to contain:<\/p>\n
00000000 00005000 PSW\r\n06004000 60000060 Read Data into location x'4000', Command Chain, SLI, x'60' byes of data\r\n08004000 00000000 TIC location x'4000'<\/pre>\nThis will cause x’60’ byes from our IPL2 record to be read into location x’4000′ and then the CCW program will TIC (branch) to get the next CCW from that location.<\/p>\n
Our IPL2 record needs to contain the necessary CCW’s and data fields to read in the IPL text from record 4. \u00a0We will read the IPL text into location x’5000′. \u00a0Our IPL2 record needs to contain:<\/p>\n
07004021 40000006 SEEK, Command Chain\r\n31004023 40000005 SEARCH ID Equal, Command Chain\r\n08004008 00000000 TIC (back to search CCW)\r\n06005000 2000**** READ Data, SLI\r\n00000000 00000004 MBBCCHHR (for Seek and Search)<\/pre>\nThe data length in the Read Data CCW should be the same as the actual length of our IPL text record.<\/p>\n
[Next – TXXIPL2D \u2013 Writing IPL Text To DASD<\/a>]<\/p>\n","protected":false},"excerpt":{"rendered":"
Now we are ready to start preparing to IPL directly from a DASD volume instead of the card reader. \u00a0When the CPU IPL’s from DASD the IPL record at CC=0000 HH=00000 R=01 will be read into memory. \u00a0Just like our … Continue reading