[Simh] retargetable assembler

[Phil Budne]

> How do you feel about the dwelling value?  The inspection came in at $133,000 for the replacement cost of your home, do you agree? The policy is currently at $205,000.

How was the inspection estimate calculated:
Was it based on current condition or replacement cost?

> Reading the Wikipedia page about Whirlwind, it mentions that the pdp1 is a direct descendent, so would a pdp1 assembler work? Or a tx0 Assembler? I don't know if these already exist or not.

There's certainly close interrelation the the development of Whirlwind, TX-0 and the PDP-1.

http://libraries.mit.edu/archives/research/collections/collections-mc/mc665.html
says:

	The U.S. Air Force provided substantial financial support for
	Whirlwind applications and it was a key component in the
	design of the Air Force's SAGE (Semi-Automatic Ground
	Environment) air defense system in the 1950s. Research
	projects at Lincoln Laboratory resulted in the further
	development of two additional computers, the MTC (memory test
	computer) and TX-0 (transistor computer), by Group 63 of
	Lincoln Lab, Division 6.

http://americanhistory.si.edu/comphist/olsen.html

Ken Olsen:

	We understood from experience that you really had to test
	every possible combination. Because [no matter] how thoroughly
	you designed things there's always something that might go
	wrong or some combination of things that might be wrong. And
	people were not about to trust the core memory unless it was
	truly tested in an environment that was tested. So we set
	about to build what we called a memory test computer. It was
	supposed to be an honest to goodness computer that would
	really run and test the memory, but not a computer that
	designed to be useful. I was given the job of building the
	computer just as soon as my thesis was done. I think I was
	still a graduate student and it cost a million dollars. I can
	remember being impressed of how much a million dollars
	was. How much work it took to spend a million dollars. Now I'm
	impressed at how little effort it takes to spend a million
	dollars. So we built a 16-bit machine.

....

	[STANDING AT THE TX-0 COMPUTER] When I was given the
	opportunity to work on a transistor computer, the idea was
	kind of new, it was exciting and we had knowledge of the very
	fast transistor which we had built a very fast computer. The
	rules were, I could hire nobody and have no space. I studied
	the rules carefully and found all the loopholes. I somehow was
	able, one way or another, to get three or four people to work
	with me. We discovered that hallway was not space. So we moved
	my office into the hall and put walls around it. We then
	traded that space for a space in the basement which was less
	desirable but bigger. With that we were able to do our work.

TX-0 was to TX-2 as MTC was to the Whirlwind.

The PDP-1 was designed by Ben Gurley, who had worked on TX-0 and TX-2.

http://www.computerhistory.org/pdp-1/ben-gurley/

	Two years after DEC was formed in 1957, Ben Gurley was brought
	on board to work on the PDP-1 with fellow engineers--and former
	Lincoln Laboratory employees--Ken Olsen, Dick Best, Bob Savell,
	Harlan Anderson, and Stan Olsen. Their computer design work at
	MIT greatly influenced the development of the PDP-1, which has
	been described as a "direct descendant" of the TX-0 and TX-2
	computers created at MIT.

You can find a PDP-1 cross-assembler at
https://github.com/simh/simtools/tree/master/crossassemblers/macro1/

I wacked at it to be PDP-1 MACRO compatible enough to assemble MACRO sources.

It has PDP-1 opcode values built in (unlike the actual implementations
back in the day, where the opcodes were defined by a source (paper)
tape.  The same is the case with the "as" assembled on PDP-7 UNIX,
which I also coaxed back to life), nonetheless it should suffice!

ISTR:
	the MACRO (and MIDAS?) assemblers got their start on TX-0.
	one of them was translated to the PDP-1 in a weekend hack attack (on a bet?)