An(other) implementation of a PDP-11 assembler and emulator that runs in the browser.
Unlike the others, this version doesn't require an operating system, and it is designed to give more meaningful errors. It also features breakpoints, and it can switch from the deult octal representation to either decimal or hex for anyone born after 1970.
I'm creating a course about how computers work. Part of it looks at internal architecture, machine code, memory, registers, processor status, and so on.
The PDP-11 is an elegant, simple, and surprisingly complete machine. It lets me talk about these things without getting in the way.
The only in-browser emulators I could find were either so realistic that they needed to boot a DEC operating system to be useful, or very terse when it came to supporting new users.
Create webpages containing placeholder divs and point this library at them.
The library will create an editor window, a machine status area, and a set of control buttons.
The editor knows about PDP-11 assembler syntax, and performs incremental assembly as you type. When it encounters a syntax error, it tries to show you just the text in error:
Whenever the source code assembles cleanly, the playground is ready to run the code. It shows STEP/RUN/RESET buttons and the contents of the processor registers (including the PSW).
As you step through the code the currently executing line is highlighted in the editor. The registers and memory dump (at the left of the source code) show when locations are read and written, along with their new values.
Clicking on a line number sets a breakpoint.
Although the environment does not have an I/O subsystem, it does emulate some
basic console output macros (.ttyout and .print).
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The built-in assembler is based on DEC's Macro-11 Assembler, but without the macros and the sectioning control.
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The PDP-11 Playground is not a complete PDP-11 computer; it's just an emulation of the processor. There's no I/O subsystem or memory management unit, so it will not boot DEC operating systems.
Copyright © 2021 Dave Thomas (pragdave)