CASMSIM - an HP Classic series calculator micro assembler and simulator Copyright 1995, 2003 Eric L. Smith (eric@brouhaha.com) $Id: README 108 2004-01-12 10:18:47Z eric $
CASMSIM consists of the CASM assembler and the CSIM simulator. It's just a quick hack, so don't expect too much. In particular it really needs an Imakefile.
Notices
CASMSIM is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation. Note that I am not granting permission to redistribute or modify CASMSIM under the terms of any later version of the General Public License.
This program is distributed in the hope that it will be useful (or at least amusing), but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program (in the file "COPYING"); if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
CASMSIM is distributed with a file named "hp45.asm" containing source code from United States patent number 4,001,569 and a file named "hp55.asm" containing source code from United States patent number 4,009,379. These two files are distributed only for your convenience; they are not part of CASMSIM, are not copyrighted by Eric L. Smith, and are not subject to the General Public License.
Background
The HP-35, the first of HP's classic series of handheld calculators, was introduced in 1972 and described as the "Electronic Slide Rule". The HP-35 was a non-programmable scientific, and was followed by the HP-45 improved scientific calculator, the HP-65 scientific programmable with card reader, the HP-55 scientific programmable with stopwatch, and the HP-70 and HP-80 business calculators. All of these calculators used essentially the same processor, which was also used in the HP 3380 Integrator, the HP 5830 and HP 5840 Gas Chromatographs, and the HP 1722 Oscilliscope.
In the HP classic series processor, unlike modern microprocessors, various instructions were interpreted by various chips. The core processor consists of the C&T (control and timing), A&R (arithmetic and registers) and the ROM or QUAD ROM chips. Additions chips may be present for data storage or program storage. Since different calculator models have different combinations of these chips, some instructions are not available on all models. For instance, the "delayed select" instructions are probably not implemented in the HP-35 and HP-80 which use single ROMs, and the "search for label" instruction is only available in the HP-65.
The design of the processor and the instruction set are described in detail in United States patents 3,863,060 and 4,001,569.
I've typed in the source code from the '569 and '379 patents which cover the HP-45 and HP-55 respectively. There are likely to be errors in my typing, as the listings in the patents are poorly reproduced. I plan to eventually dump the ROMs from actual calculators to verify my typing. For that matter, the code in the patents might not be identical to that in production units.
Various other United States patents assigned to Hewlett-Packard appear to contain source listings of ROMs of other HP calculators:
3,863,060: HP-80
4,099,246: HP-65 (only first half of ROM)
4,291,385: HP-65 (only first half of ROM)
CASM
I used GNU tools to build CASM; specifically GCC 2.5.8, Flex 2.4.7, Bison 1.22, and Make 3.71. I don't believe in using ugly preprocessor macros to make my code compile on non-ANSI compilers. Lex won't work because I don't know how to make it take input from a string. Earlier versions of Flex don't seem to work either, probably because they handle input differently.
CASM requires a single command line argument to specify the source code file.
CASM derives names for the object and listing files from the source filename by replacing the extension (everything after the last dot, typically "asm") with "obj" or "lst". If the source filename doesn't have an extension CASM adds one. The object file format is one word per line with the five digit octal address, a colon and the instruction word in hexadecimal.
I personally prefer my assembly source code to be in all lower case, so it doesn't look like it is shouting at me. All the source code I have typed in from patents is in lower case, but CASM is case insensitive so if you prefer emphatic source code be my guest.
CASM considers the keywords which are used to form instructions to be reserved words, so they can't be used as labels. HP's assembler was more flexible in this regard; I had to change the label "go" in the HP-55 source code to "go_".
CASM does a better job of displaying the branch target addresses than the HP assembler did. It will actually show the correct target address based on the delayed select instructions, unless the delay instruction is in the last word of a page. CASM has a ".rom" directive which can be used to provide the rom number. This is roughly equivalent to the origin directive in a typical assembler, except that CASM always start assembling code at location 0 of the selected ROM.
Because HP assembled each ROM separately, they were able to use the same symbols in multiple ROMs. CASM therefore has a separate name space and keeps a separate symbol table for each ROM.
CASM has a .symtab directive which causes the symbol table to be printed to the listing file. If the source file contains multiple ROMs, each ROM should have its own .symtab directive.
The file "hp55.asm" when assembled with CASM will produce one warning, which will be printed to standard out twice (once during each pass). This warning can be ignored as it is the result of CASM being pickier than the HP assembler about forms of the "go to" instruction.
If you can't get CASM working I have made the file listings.tar.gz available separately. It includes hp45.lst and hp55.lst files which can be used with CSIM.
CSIM
CSIM is a simulator for the hardware of the HP Classic series of calculators. It should be capable of simulating the HP-35, HP-45, HP-55, HP-70, and HP-80. With some additional work it should eventually be able to simulate the HP-65.
CSIM currently uses the X window system, although by replacing the file xio.c with an alternate file that implements the three functions whose prototypes are in xio.h, it should be possible to make it work with any reasonable input and output devices. The X interface currently only supports the HP-45 keyboard legends.
Since CSIM simulates the actual hardware, it is of little use unless you have an image of the ROM code from the calculator.
CSIM uses a single command line argument to specify the assembly listing file. If no argument is found, CSIM will try to find a file using the concatentation of the name under which it was invoked and ".lst". This allows you to (for instance) link CSIM to "hp45" and have it automatically try to load and run "hp45.lst".
At this point CSIM is known to mostly work with the HP-45 ROM image, but I haven't tested it much and I haven't verified the ROM image. There are serious problems with the HP-55 image, which may be CSIM bugs or they may be errors in my typing of the assembly sources. The keyboard layout and legends are currently hardcoded for the HP-45 in xio.c.
There are two compile time options currently defined in the Makefile:
-DUS_TIMER
Enables the code to use the BSD-style interval timer to prevent the
simulator from executing more than 35 microinstructions every 1/100
of a second. This allows for an approximation of the performance of
the real HP calculators. If your operating system doesn't support
the setitimer() system call you'll have to take this define out or
write equivalent code yourself. With this define in place, CSIM uses
sufficiently little CPU time that it isn't a problem to leave it
running all the time (at least on my DX4-100, a VAX-11/725 might be a
different story). It doesn't make any noticable contribution to the
load average under Linux. Under BSDI/386 the load average must be
computed wrong (or at least differently), as it pegs the load average
at one (when nothing else is running).
-DENTER_KEY_MOD
Causes the ENTER^ key to generate the keycode for the normally
unused right hand button under the key. On the HP-45 this button
works just like the normal ENTER^ button except when pressed after
RCL, in which case it activates the undocumented and unsupported
stopwatch mode. On a real HP-45 this button can also be "pressed"
as a phantom key by simultaneously pressing CHS, 7, and 8. It is
fairly hard to consistenly press the three keys simultaneously, so
often this was done by the "penny trick". CSIM doesn't support
multiple key presses at all, so this define is necessary to get into
stopwatch mode. On my DX4-100 when the load average is near zero,
the stopwatch has an error of a few seconds per hour, which is better
than a real HP-45 without the crystal modification. If the load
average approaches one the stopwatch will lose a lot of time. Don't
blame me if you try to use it and burn your eggs.
Credits (and blame)
CASMSIM was originally written by Eric Smith. Any bugs in it are almost certainly my fault.
Peter Monta developed a specialized OCR program for use on the ROM listings in the US patents, and found one typo in my HP-45 source code and several in my HP-55 source code. He also provided modifications to xio.c to support the HP-55 keyboard.
Dave Hicks, of hpmuseum.org fame, translated CSIM to Java:
http://www.hpmuseum.org/simulate/sim45.htm
Thanks also to HP for having made such great products in the first place, without which all of this would have been unnecessary. :-)