I was researching the disappearance of an STCB field (STCBDUCR) in
z/OS R2.4 maclibs when I noticed a discrepancy that has me puzzled:
1) Up until zOS R2.3, the STCBDUCR field used to contain the 31-bit
REAL address of the Dispatchable Unit Control Table (DUCT).
2) But in the z/OS R2.4 maclibs, in the STCB mapping macro (IHASTCB),
the STCBDUCR field was removed, and a new 64-bit field was added:
STCBDCR8. This is caption as "Real address of the DUCT".
3) When a DUCT is active, it's real address is carried in Control
Register 2 ("CR2"). So I went to the -12 edition of Principles (new
with advent of the Z15 machine) to see if the definition of CR2 had changed.
4) To my surprise, it had not!
- It still describes the DUCTO as... "Bits 33-57 of control
register 2, with six zeros appended on the right, form a 31-bit real
address that designates the beginning of the dispatchable-
unit control table".
- And it still shows bits 0 thru 32 of CR2 as being reserved!
So the discrepancy is this:
- The STCB has been prepared to hold an 8-byte wide real address
of the DUCT.
- Yet the hardware (i.e. CR2) still only supports a 31-bit real address!
Can anyone shed some light on this?
TIA
Dave Cole
ColeSoft Marketing
414 Third Street, NE
Charlottesville, VA 22902
EADDRESS: [email protected]
Home page: www.colesoft.com
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Tools: z/XDC for Assembler debugging
c/XDC for C debugging
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