There are three controls on the console bulkhead of these systems:
| Triangle-in-circle-paddle: | halt enable. |
| dot-in-circle: |
halt (BREAK) is enabled, and auto-boot is disabled. |
| dot-not-in-circle: |
halt (BREAK) is disabled, and auto-boot is enabled. |
| Three-position-rotary: | power-up bootstrap behaviour |
| arrow: | normal operation. |
| face: | language inquiry mode. |
| t-in-circle: | infinite self-test loop. |
| Eight-position-rotary: |
console baud rate selection select the required baud rate; read at power-up. |
Also present on the bulkhead is a self-test indicator: a single digit
LED display. This
matches the final part of the countdown displayed on the console or
workstation, and can be used by a service organization to determine the
nature of a processor problem. The particular countdown sequence varies
by processor type, consult the hardware or owner's manual for the processor,
or contact the local hardware service organization for information the
self-test sequence for a particular processor module.
Note that self-tests
2, 1 and 0 are associated with the transfer of control from the console
program to the booting operating system.
[Steve Hoffman]
For all formats, the fraction is normalized and the radix point assumed to
be to the left of the MSB, hence 0.5 <= f < 1.0. The MSB, always being 1,
is not stored. The binary exponent is stored with a bias varying with
type in bits 14:n of the lowest-addressed word.
| Type | Exponent bits |
Exponent bias |
Fraction bits (including hidden) |
| F | 8 | 128 | 24 |
| D | 8 | 128 | 56 |
| G | 11 | 1024 | 53 |
| H | 15 | 16384 | 113 |
The layout for D is identical to that for F except for 32 additional fraction bits.
Example: +1.5 in F float is hex 000040C0 (fraction of .11[base 2], biased exponent of 129)
[Steve Lionel]
http://www.compaq.com/alphaserver/vax/Jim Agnew maintains a MicroVAX/VAXstation FAQ at:
http://anacin.nsc.vcu.edu/~jim/mvax/mvax_faq.htmlJames Lothian maintains a VAX-11/750 FAQ at:
http://www.dcs.napier.ac.uk/~oose5002/750faq.htmlThe VAXstation 3100 Owner's Guide:
http://www.whiteice.com/~williamwebb/intro/DOC-i.htmlA field guide to PDP-11 (and VAX) Q-bus and UNIBUS modules can be found at:
http://metalab.unc.edu//pub/academic/computer-science/history/pdp-11/hardware/field-guide.txtVarious VAX historical information (also see VMS1) can be found at:
http://telnet.hu/hamster/vax/e_index.html
System disks larger than 1.073 gigabytes (GB) - 1FFFFF hexidecimal blocks - are not supported on any member of the VAXstation 3100 series and on certain older members of the MicroVAX 3100 series, and are not reliable on these affected systems. (See below to identify the affected systems - the more recent members of the MicroVAX 3100 series systems are not affected.)
Various SCSI commands used by the boot drivers imbedded in the console PROM on all members of the VAXstation 3100 series use "Group 0" commands, which allow a 21 bit block number field, which allows access to the first 1FFFFF hexidecimal blocks of a disk. Any disk references past 1FFFFF will wrap - this wrapping behaviour can be of particular interest when writing a system crashdump file, as this can potentially lead to system disk corruptions should any part of the crashdump file be located beyond 1.073 GB.
More recent systems and console PROMs use "Group 1" SCSI commands, which allow a 32 bit block number field.
There was a similar limitation among the oldest of the MicroVAX 3100 series, but a console boot PROM was phased into production and was made available for field retrofits - this PROM upgrade allows the use of the "Group 1" SCSI commands, and thus larger system disks. There was no similar PROM upgrade for the VAXstation 3100 series.
Systems that are affected by this limit:
[Steve Hoffman]
The exact syntax is console-specific, recent VAX consoles tend
to use the following:
>>> BOOT/R5:flags
| Bit | Meaning |
|---|---|
| 0 | RPB$V_CONV Conversational boot. At various points in the system boot procedure, the bootstrap code solicits parameter and other input from the console terminal. If the DIAG is also on then the diagnostic supervisor should enter "MENU" mode and prompt user for the devices to test. |
| 1 | RPB$V_DEBUG Debug. If this flag is set, VMS maps the code for the XDELTA debugger into the system page tables of the running system. |
| 2 | RPB$V_INIBPT Initial breakpoint. If RPB$V_DEBUG is set, VMS executes a BPT instruction immediately after enabling mapping. |
| 3 | RPB$V_BBLOCK Secondary boot from the boot block. Secondary bootstrap is a single 512-byte block, whose LBN is specified in R4. |
| 4 | RPB$V_DIAG Diagnostic boot. Secondary bootstrap is image called [SYSMAINT]DIAGBOOT.EXE. |
| 5 | RPB$V_BOOBPT Bootstrap breakpoint. Stops the primary and secondary bootstraps with a breakpoint instruction before testing memory. |
| 6 | RPB$V_HEADER Image header. Takes the transfer address of the secondary bootstrap image from that file's image header. If RPB$V_HEADER is not set, transfers control to the first byte of the secondary boot file. |
| 7 | RPB$V_NOTEST Memory test inhibit. Sets a bit in the PFN bit map for each page of memory present. Does not test the memory. |
| 8 | RPB$V_SOLICT File name. VMB prompts for the name of a secondary bootstrap file. |
| 9 | RPB$V_HALT Halt before transfer. Executes a HALT instruction before transferring control to the secondary bootstrap. |
| 10 | RPB$V_NOPFND No PFN deletion (not implemented; intended to tell VMB not to read a file from the boot device that identifies bad or reserved memory pages, so that VMB does not mark these pages as valid in the PFN bitmap). |
| 11 | RPB$V_MPM Specifies that multi-port memory is to be used for the total EXEC memory requirement. No local memory is to be used. This is for tightly-coupled multi-processing. If the DIAG is also on, then the diagnostic supervisor enters AUTOTEST mode. |
| 12 | RPB$V_USEMPM Specifies that multi-port memory should be used in addition to local memory, as though both were one single pool of pages. |
| 13 | RPB$V_MEMTEST Specifies that a more extensive algorithm be used when testing main memory for hardware uncorrectable (RDS) errors. |
| 14 | RPB$V_FINDMEM Requests use of MA780 memory if MS780 is insufficient for booting. Used for 11/782 installations. |
| <31:28> | RPB$V_TOPSYS Specifies the top level directory number for system disks with multiple systems. |
The TOY value is used in conjunction with a year value stored in SYS.EXE - the TOY clock resolution is circa 497 days, meaning that a SET TIME must be issued early each year in order to keep the SYS.EXE and TOY clock values synchronized, and must also be issued whenever a new or different SYS.EXE image is in use.
The VAX Interval Time is used to keep the running time, and this has a specified accuracy of .01%. This is a drift of approximately 8.64 seconds per day.
Any high-IPL activity can interfere with the IPL 22 or IPL 24 (this depends on the VAX implementation) clock interrupts - activities such as extensive device driver interrupts or memory errors are known to slow the clock.
Also see ALPHA1, DECW13, and SUPP3.
[Antonio Carlini]
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