MS11 and MSV11 — memory

MEM is a memory card for a machine whose backplane carries none, or not enough. It answers one range of addresses out of the board’s own memory: the board’s bus engine serves every read and write there by itself, so the machine sees memory at bus speed. It holds no registers and appears nowhere in the I/O page; an operating system finds the top of memory by the bus timeout above it, as it does with any memory card.

UNIBUS · UniBone

The card is of type MS11, in the 18-bit address space. Placed at 0 with the default size, it fills everything below the I/O page: 248 KB.

QBUS · QBone

The card is of type MSV11. On a 22-bit QBUS the top 128 KB below the I/O page, from 17360000, belong to the processor module: a KDJ11 answers its boot ROM there without a bus cycle, so nothing the board can ask the bus reveals a collision. A card placed there is written over the bus and read back as ROM, and the ROM’s own memory test stops on a word it did not write. The card therefore ends at 17357776 at the most, and a placement reaching further is refused. Placed at 0 with the default size, it fills those 3960 KB.

What the machine sees

Memory	Word and byte reads and writes over the range startaddr..endaddr
Registers	None. Parity and the CSR at 772100 are not modelled
Contents	Kept across INIT and power cycles, so a program loaded and started from the console survives the restart that starts it. Cleared when the card takes up a range

Placing it

The card goes above the memory the machine already carries. Two cards answering the same address drive the bus against each other, so the card reads its range over the bus before it takes it and refuses when anything answers there. The Machine screen’s memory probe sizes the memory the machine carries, and the memory map on the dashboard shows the ranges the board answers.

The range is set by startaddr and size. POST /api/memory/place sets both as one placement, which is how a configuration names the range. Set one parameter at a time, and a card moving from one range to another can pass through a placement that is refused.

The board answers two ranges out of its memory: this card’s and one device window, such as a VCB01 framebuffer or the MRV11-D array in memory space. The two may not overlap.

An emulated processor supplies its own memory when it is enabled, everything below the I/O page that no card answers. A MEM card placed before it keeps its range.

What has been verified

• On a KDJ11-SD with 1.5 MB of its own, MEM at 06000000 with 2424 KB carries the machine to 17357776, and 2.11BSD reports phys mem = 4055040, 3960 KB.

Parameters

Settings

What a configuration stores and an operator sets.

Parameter	Short	Value	Default	What it is
startaddr	sa	octal	0	first address the card answers
size	sz	text	all the bus leaves to memory: 248 KB with 18-bit addresses, 3960 KB on a 22-bit QBUS	how much memory the card carries
probe	pr	0 or 1	1	check the range answers to nothing before claiming it

Status

What the device reports as it runs. A configuration does not store these.

Parameter	Short	Value	What it is
endaddr	ea	octal	last address the card answers
readlamp	rdl	0 or 1	machine is reading the card
writelamp	wrl	0 or 1	machine is writing the card

It also carries the parameters under parameters every device has.

In detail

startaddr

The first address the card answers, octal and even. Changing it, or size, moves the card: a card in the machine gives up its range and takes the new one, probed as probe says, and the range it takes up comes up cleared. A range that is refused leaves the card where it was.

size, endaddr

How much memory the card carries, written as a card is described — 256 KB, 2 MB, or a count of bytes — and read back that way. endaddr, the last address the card answers, follows from it and startaddr. The default covers everything the bus leaves to memory, which is the whole machine on a backplane that carries no memory of its own.

The range has to end below the I/O page. On a 22-bit QBUS it also has to end below 17360000: the top 128 KB under the I/O page belong to the processor module, where a KDJ11 answers its boot ROM without a bus cycle, so nothing on the bus can see the collision. A range that breaks either rule is refused, and the error says why.

readlamp, writelamp

Lit while the machine reads or writes the card, one lamp per direction.

probe

Before the card claims a range it reads the range over the bus, and refuses when anything answers there: a range claimed over memory the machine already carries puts two cards on one bus cycle. The probe reads both ends and words in between. A range found clear is remembered on the board, and enabling the card on the same range again goes in on that record; moving the card probes again. Set this to 0 only where the probe cannot work: a bus with nothing on it to grant the board the cycles it probes with.