The purpose of AR mode is to allow access to other address spaces. Yes, a length of zero mean that the content of the corresponding address register will not be used, but there is nothing to suggest that the length is zero.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 עַם יִשְׂרָאֵל חַי נֵ֣צַח יִשְׂרָאֵ֔ל לֹ֥א יְשַׁקֵּ֖ר ________________________________________ From: IBM Mainframe Discussion List <[email protected]> on behalf of Robin Vowels <[email protected]> Sent: Tuesday, March 18, 2025 10:13 AM To: [email protected] Subject: Re: AR Mode: MVCL R0,Rx No; MVCL Rx,Ry Yes External Message: Use Caution Enlighten me. What is the purpose of AR mode? Does not a length of zero mean that the content of the corresponding address register not be used? On 2025-03-18 05:32, Richard Zierdt wrote: > The following is documented in PoPs, but what the hey. > > Primary (ASC) Mode: MVCL R0,Rx is fine > > AR (ASC) Mode: MVCL R0,Rx is *not* fine — AR0 is not honored > > The PoPs manual on MVCL: > > "In the access-register mode, the contents of access > register R1 and access register R2 are compared. If > the R1 or R2 field is zero, 32 zeros are used rather > than the contents of access register 0. " > > There is probably a reason why AR0 is not supported as MVCL operands; > it's just that it's inconsistent with the corresponding behavior in > Primary ACS mode. > > Richard Zierdt ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
