VCB01 — QVSS monochrome graphics

The VCB01 (M7602), also called the QVSS, is the monochrome video board of the VAXstation II: a 1024 × 864 bitmap in 256 KB of video memory on the QBUS, a 6845 CRT controller, a hardware cursor, an interrupt controller, and a serial chip carrying an LK201 keyboard and a mouse. QUniLator presents its registers and its video memory to the processor and draws the screen in the browser, and on an X server when one is named. It is listed as vcb01, of type VCB01.

QBUS · QBone

The VCB01 is a QBUS card. A UniBone has no emulated display.

What the machine sees

Registers	32 words at 17777200: the CSR, cursor position, pointer position, the CRT controller’s address and data, the interrupt controller, and from base+40 the SCN2681 serial chip
Video memory	256 KB at bank × 256 KB — 16000000 to 16777776 with the default bank 016. The bank reads back in CSR bits 11 to 14
Screen	1024 pixels wide. The height follows what the driver programs into the CRT controller, 864 lines until it does
Keyboard	An LK201 on channel A of the serial chip
Pointer	A mouse on channel B, its buttons in the CSR. Base+4 and base+6 also give the pointer’s absolute position on the screen, which the original board does not have; bit 15 of base+4 marks it present
Interrupts	BR4, through the board’s interrupt controller, which gives each source — serial chip, vertical sync, pointer, buttons — the vector the driver programs. Vertical sync comes 60 times a second

Using it

1. Find room for the video memory. The bank needs a free 256 KB in the 22-bit address space. The default, 016, sits just below the I/O page, so the machine’s memory must end below 16000000 (3.5 MB). A memory card that fills the whole 4 MB space collides with every bank; the board’s own MEM device and the video memory are served out of two separate ranges that may not overlap. GET /api/memory/map shows what answers where.
2. Add vcb01 on the Configurations screen. To have the screen on an X server as well as in the browser, set display to that server, such as myhost:0.
3. Enable it. The VCB01 card on the dashboard shows the screen; click it to give it keyboard and pointer.

bank and display can only be changed while the card is disabled. Enabling is refused when the bank cannot be served or a named display cannot be reached, and the log says which.

2.11BSD carries no driver for it. The QVSS driver, qv, is part of the VAX BSD and Ultrix systems.

What has been verified

• A standalone PDP-11 program, vcbdemo.mac, run on a real PDP-11/73, programs the CRT controller, draws a test pattern into video memory and turns the video on; the pattern appears on the X display. A key pressed shows its LK201 code on the screen, and moving the pointer over the window leaves a trail behind the hardware cursor.
• DEC wrote no XXDP diagnostic for the VCB01, so programs that drive it are its test.

Parameters

Settings

What a configuration stores and an operator sets.

Parameter	Short	Value	Default	What it is
display	disp	text	empty	X display carrying the screen, e.g. “host:0”
bank	bk	octal	16	video memory bank, 256 KB each: address = bank * 1000000
refreshrate	rr	number, Hz	30	screen updates per second
largemonitor	lm	0 or 1	1	report a 19-inch monitor rather than a 15-inch one

It also carries the parameters under parameters every card on the bus has.

In detail

display

An X server to show the screen on as well, as an X display name such as host:0; a host name is resolved on the board before connecting. Empty, the screen is drawn to the web interface only, where the VCB01 card on the dashboard shows it and takes keyboard and pointer. Named, the screen opens in an X window when the card is enabled, and keyboard and pointer work there too; a display that cannot be reached refuses the enable. Can be changed only while the card is disabled.

bank

The card’s memory bank switch: the 256 KB of video memory answer at bank x 256 KB, 0 to 016, and a driver reads the setting back from CSR bits 11 to 14. 016 puts the bitmap at 16000000..16777776, the highest bank below the I/O page. The bank needs a free stretch of bus address space: the machine’s own memory has to end below it, and the MEM device’s range may not overlap it - enabling the card refuses a bank that collides with MEM. Enabling clears the video memory. Can be changed only while the card is disabled.

refreshrate

How often the screen is redrawn, 1 to 60 times a second. Each pass sends only the lines that changed, and keyboard and pointer input are taken in at the same pace. The vertical sync interrupt a driver sees runs at 60 Hz whatever this is set to.

largemonitor

The monitor size the card reports in CSR bit 0: on, a 19-inch monitor that shows all 864 lines; off, a 15-inch one. Set it while the card is disabled.