On Sun, 12 Feb 2023 at 07:24, Joe Monk <joemon...@gmail.com> wrote: > Page 4-82 of the PoOPS says: > > "If CPU power-on reset establishes the configuration, then it sets the > architectural mode to one of the following: > > - > > The ESA/390 mode (when neither the ESA/390-compatibility-mode facility > nor the CZAM facility is installed) > - > > The ESA/390-compatibility mode (when the ESA/390-compatibility-mode > facility is installed) > - > > The z/Architecture architectural mode (when the CZAM facility is > installed)" > > > So, when a machine is powered on and has both CZAM and 390-CM, what is the > power-on configuration of the CPU? >
Chapter 5 says "The ESA/390-compatibility mode is available only to a virtual machine under the control of a hypervisor program such as z/VM." (This is logically the replacement/extension of XC-mode, I believe.) So how would your question arise? Presumably the (virtual) machine will be in ESA/390-compatibility mode at (virtual) POR, and the facility bits as seen by (virtual) STFLE will show that. These bits in the facility list returned by STFLE seem relevant: 1 The z/Architecture architectural mode is installed. 2 The z/Architecture architectural mode is active. When bits 2 and 168 are both zero, the ESA/390 architectural mode is active. When bit 2 is zero and bit 168 is one, the ESA/390-compatibility mode is active. 168 The ESA/390-compatibility-mode facility is installed in the configuration. Surely the hypervisor will set bit 2 off and bit 168 on when it dispatches a virtual machine in ESA/390-compatibility mode. What it does with bit 1, I don't know, but I can't see that it affects anything. Always the same voices speculating here, eh... Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
