P85x Simulation

P85x Simulation: P853/4, P858/9 (P857) running MAS

P85x is published in two flavors:

256Kb machine, running MAS release 9 (MASR) from a 80 Mb moving head CDC disk (2 disks are configured)
256Kb machine, running MAS release 8.12 (MASRA) from a 5.2 Mb moving head X1216 disk (4 disks are configured)

MAS stands for Multi Application System and it allows to use a physical P85x machine as multiple virtual machines. The physical machine uses a MMU (Memory Management Unit): a hardware feature which allocates a 64Kb memory window of the physical memory to a particular virtual machine. Allocation is done by means of 4Kb memory pages; 16 total per virtual machine. The memory pages do not need to be consecutive in the physical memory. By changing he MMU registers, the window in the physical memory is changed.

The available MAS releases are configured for P853/4 or P858/9; these MAS releases do not run on a P857, which has a different PSW. The releases are socalled "extended system mode" releases, which means that the system is able to run in three states:

System mode: No MMU: the 1st 64Kb memory block is used; privileged instructions can be executed (operating system mode).
Extended system mode; MMU is used; privileged instructions can be executed (operating system mode).
User mode; MMU is used; no privileged instruction allowed (used by user programs)

The P857 only supports "System mode" and "User mode". Extended system mode was invented for the successors of the P857, because the later MAS releases could not run in only the first 64Kb block. Extended system mode is indicated by a bit in the PSW which is not available in the P857.

The simulators are executed as a Perl program, either on Windows or Linux. To run a simulator, 4 Perl modules must be installed:

Term::ReadKey
Time::Hires
IO::Handle
Tk

Because no MAS system generation pack is available, the available MAS systems are changed by means of patches. MASR on the CDC disk is patched with the file patch3b.hex; MASRA on the X1216 disk is patched with the file patchmasra1.hex. The MASR patch inserts support for 2 additional teletypes (TY08 and TY09) and a papertape reader (PR20); the MASRA patch inserts one additional teletype (TY09), a papertape reader (PR20) and a lineprinter (LP07).

After the simulator is started, five windows become visilble: 1 control panel, 3 teletype windows and a lineprinter window (see picture above). Pressing the IPL button (on the Control Panel, see picture above) loads and starts MAS, the patch is loaded and the System Machine is started, using console TY10. After typing in date and time the system machine prompt "FCL:" becomes visible.

MAS supports 3 types of (virtual) machines:

one System Machine, which runs the operating system MAS
zero or more Foreground Machines to run (real time) user applications
zero or one Background Machine to run batch applications

With the System Machine the Fore and Background Machines are defined and started. With the catalogued procedure %%BMS the background machine is defined and started and uses console TY08. %%FGR defines and starts a foreground machine using console TY09.

MAS uses 3 Control Languages:

SCL: System Control Language, used by the System Machine
FCL: Foreground Control Language, used to control the Foreground Machines
BCL: Batch Control Language, used to control the Background Machine

The picture above shows a Fortran job execution in the backgound (TY08: compile, link), while the Librarian is executing in the foreground machine (TY09).

MAS emulation software

MAS is a complex system which cannot be explained in a few pages. Fortunately most of its documentation is still available and details about its operation can be found in the documents below.

MAS documentation

MAS8 part1 1-Introduction, 2-General principles, 3-Data Management, 4-Operation, 5-Operator Commands

MAS8 part2 6-The System Machine, 7-System Command Language

MAS8 part3 8-The Background Machine, 9-Background/Batch Command Language

MAS8 part4 10-Foreground Machines, 11-Foreground Command Language

MAS8 part5 appendix A,B A-System Generation, B-Syntax

MAS8 part5 appendix C C-Monitor Requests

MAS8 part5 appendix D,E,F,G D-Utilities, E-Flexible Disk Drivers, F-User drivers, G-Internal Structure

MAS8 Trouble Shutting Guide

80Mb CDC disk control unit

MAS Software Processors part 1 Assembly Language

MAS Software Processors part 2 Assembler