How to IPL & Debug
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Uploading
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When uploading LINUX390.LOADER be sure to specify 'binary mode' during 
ftp.  It will upload to a single record of 400 bytes; however, you want 
5 records of 80 bytes (of fixed length).  You can do this with XEDIT,
type 'next' to position the cursor, and 'split 81 161 241 321' to
split the line.  Finally, make it a fixed reclen with:
'copy / ( recfm F lrecl 80'

Booting
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Currently, the boot process works as follows:
A rexx script LINUXTXT.REXX will accept a kernel you've uploaded,
read its ELF header, and punch out a card deck containing that
kernel.  You need to preface this deck with the binary
LINUX390.LOADER, put the whole thing on a device and IPL.

Most convenient is to IPL from your reader spool.  The exec
LINUXIPL.EXEC will punch out the kernel to the RDR spool.

To boot, type 'CP IPL 00C CLEAR' and you should be on your way.

Note that '00C' is the virtual device usually associated with 
the reader sppol, you will want to verify that this is the case
for your account with 'Q ALL'.

Debugging
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You will want to debug in CP.  So, during boot, you will want to
'CP IPL 00C CLEAR STOP'.  Then set any tracepoints you want, and 'B'.

Some handy commands:
TRACE ALL        trace all instructions
TRACE END        clear all tracepoints
TRACE PROGRAM    trace program interrupts
Begin            run the thing
Query TRACE      show trace status
Display G0-16    show general registers 0-16
Display X0-16    show control registers 0-16
Display PSW ALL  show old and new psw's for all interupts
Display SCHIB    display subchannel info block ...
STORE G5 ...     load a value into GPR 5
STORE PSW ...    load a new PSW ...