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Ross Wilson
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README.md
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README.md
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##STATUS
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The current state of the emulator is:
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The main CPU emulation seems complete. There is still some work to be done on IOT instructions.
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The display isn't working AT ALL yet.
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##The Imlac
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When I was doing post-graduate study at Sydney University one fun machine I
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worked on was an [Imlac PDS-4](http://en.wikipedia.org/wiki/Imlac_PDS-1).
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This was a 16 bit vector graphics minicomputer with a general purpose main CPU
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and a specialised display CPU - all implemented with 7400 series chips. It had
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real core memory, a papertape reader/punch, a trackball and a lightpen. Later
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on it acquired 8-inch floppy drives but few people used these as they were too
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unreliable. Besides, there's just something about papertape!
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The attraction of the machine was its simplicity, its graphics capability and
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that it ran [Spacewar!](http://en.wikipedia.org/wiki/Spacewar!) I have many
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fond memories of this machine. It was the first machine that I programmed in
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assembler.
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The Imlac has long since gone from the university.
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No one knows what happened to it.
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There is a little information online:
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* Tom Uban's [Imlac picture gallery](http://www.ubanproductions.com/imlac.html) and [software library](http://www.ubanproductions.com/imlac_sw.html)
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* The [Blinkenlights](http://www.blinkenlights.com/classiccmp/imlac/) archive of Imlac information
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* Imlac at [old-computers.com](http://www.old-computers.com/museum/computer.asp?st=1&c=1295)
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* Inevitably, there is an [Imlac Facebook page](http://www.facebook.com/pages/Imlac-PDS-1/124593560918139)
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It's a little sad to see this machine fade from memory. I wrote an emulator for
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the Imlac in C with an X display window quite a while ago, but didn't proceed
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with it, possibly because it would only run on Linux. Now I would like to
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experiment with a rewrite in Python and use wxPython or pySide for the graphics.
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The [repository](https://) holds the code.
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###Overview
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The Imlac was a simple machine that was driven in the old style: the user sat at
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the screen and loaded a papertape, set the PC address and then pressed the RUN
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button. Observing the address lights as the program ran could tell you
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something about the operation of your code. To debug your program you could
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paddle around in core and look at the contents of various addresses. Really
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steam-powered stuff!
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Since core memory is non-volatile it was possible to switch the machine off and
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turn it on days later and find your program and data still in memory. This
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emulator recreates this behaviour by writing the contents of core memory to a
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file when terminating. This *core* file is read in when the emulator starts.
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This way we can emulate the behaviour of core memory.
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To emulate this style of operation as much as possible, the console version of
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pymlac takes a series of *operations* arguments that are performed left to
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right. These operations are things such as loading a papertape into the reader,
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examining memory contents, setting the data switches or setting the machine run
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address.
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###Console usage
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The console version of pymlac is used:
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```
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pymlac [ <option> ]*
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```
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That is, the user may specify zero or more options interspersed in any manner
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required. The options are:
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```
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-b (ptr | tty | none) sets the bootstrap ROM code:
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ptr uses the papertape bootstrap ROM
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tty uses the teletype bootstrap ROM
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none uses no bootstrap ROM
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```
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```
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-c clears core except for any bootstrap ROM, if used
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```
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```
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-d <value> sets the console data switches to the <value>
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```
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```
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-h prints this help
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```
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```
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-ptp <file> loads a file on to the papertape punch
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```
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```
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-ptr <file> loads a file on to the papertape reader
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```
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```
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-r (<address> | pc) executes from <address> or the current PC contents
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</pre>
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<pre>
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-s <setfile> sets memory adress values from <setfile>
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</pre>
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<pre>
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-t (<addr1> [,<addr2>] | off) controls the execution trace:
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-t 0100 trace from address 0100 (octal)
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-t 010,200 trace from 0100 octal to 200 decimal
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-t off turns trace off
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</pre>
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<pre>
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-ttyin <file> loads a file on to the teletype reader
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</pre>
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<pre>
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-ttyout <file> loads a file on to the teletype writer
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</pre>
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<pre>
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-v <viewfile> views contents of memory addresses from file
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</pre>
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<pre>
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-w (on | off) controls ROM write property:
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-w on ROM addresses are writable
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-w off ROM addresses are write protected
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</pre>
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If we wanted the pymlac machine to load a papertape file and run at address
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0100 with trace between 0110 and 0120 we would do:
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`pymlac -b ptr -ptr test.ptp -r 040 -t 0110,0120 -r 0100`
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This would load the corefile, set the ROM to the papertape bootstrap, load the
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file test.ptp on the papertape reader and start execution at address 040 (the
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normal bootstrap ROM start address). The bootstrap runs and loads the papertape
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into memory and the machine then halts. The trace is set to be within the
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address range [0110, 0120] and the machine starts execution at 0100 and then
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again halts. The core file is saved.
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Given the persistence of the emulated core contents, the above single command could have been executed in this manner:
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`pymlac -b ptr -ptr test.ptp -r 040`
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`pymlac -t 0110,0120 -r 0100`
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If we wanted to use an existing core file from yesterday that contained a
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program that reads a data file from the TTY reader and we wanted to look at the
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contents of some parts of memory after running the program, we would do:
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`pymlac -ttyin data.tty -r 0100 -v read_memory`
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This would load the existing core file, mount the data file on the TTY reader,
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start execution at 0100, after which the machine halts. Then the contents of
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memory addresses specified in the file 'read_memory" is displayed. The core
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file is saved.
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And finally, if we just want to set some memory values in core, we would do:
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`pymlac -s setdatafile`
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Which loads the existing core file, sets some addresses to values given in the
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file 'setdatafile' and then saves the core file.
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