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Jeff Parsons 2016-04-30 08:33:26 -07:00
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31
devices/pc8080/machine/test/README.md
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@ -14,18 +14,35 @@ machines:
This is a test of [PC8080](/modules/pc8080/), a new 8080-based machine emulator being added to the
PCjs Project.
This test machine loads a copy of the
The test machine below loads a copy of the
[8080 Exerciser](https://web.archive.org/web/20151006085348/http://www.idb.me.uk/sunhillow/8080.html)
(specifically, [8080EX1](/devices/pc8080/rom/test/8080EX1.MAC)) and intercepts *just* enough of the exerciser's
CP/M calls to display its progress.
(specifically, [8080EX1](/devices/pc8080/rom/test/8080EX1.MAC)) and intercepts the exerciser's CP/M console
calls so that you can see its progress in the Control Panel window. This is a "headless" test machine
(no keyboard or display), so that's all you get.
The good news: PC8080 passes all the 8080 Exerciser tests. At 2Mhz, the tests do take quite a while,
but you can click the speed button while the machine is running to increase the simulated speed; it will
wrap around to 2Mhz if you try to exceed the maximum speed that your system supports.
The good news: PC8080 passes all the 8080 Exerciser tests. And it doesn't do it by using all sorts of weird
"flags tables", which most other 8080 emulations seem to fall back on.
Like all the other CPU emulations in the PCjs Project, PC8080 never "calculates" the flags unless/until they are
actually required, which considerably speeds up all arithmetic operations.
Of particular note are the 8080's subtract,
compare, and decrement operations, which actually perform addition, not subtraction, by using two's complement
arithmetic in "stages": the first stage (inverting the source operand) occurs *before* the addition, and the second
stage (incrementing the inverted operand) occurs *after* the addition. And it appears to be the result of the *first*
stage, not the second, that determines the state of the Auxiliary Carry flag (AF).
At 2Mhz, the 8080 Exerciser tests take quite a while, but you can click the speed button while the machine is running
to increase the simulated speed; it will revert to 2Mhz when you exceed the maximum speed that your system supports.
NOTE: The original [8080 Exerciser website](http://www.idb.me.uk/sunhillow/8080.html) is currently unavailable,
so we refer you to the copy on
[archive.org](https://web.archive.org/web/20151006085348/http://www.idb.me.uk/sunhillow/8080.html).
The 8080 Exerciser has also been "forked" on [GitHub](https://github.com/begoon/8080ex1).
The 8080 Exerciser source code has also been "forked" on [GitHub](https://github.com/begoon/8080ex1).
{% include machine.html id="test8080" %}
8080 Online Resources
---
[8080 Opcode Map](http://pastraiser.com/cpu/i8080/i8080_opcodes.html)