53 lines
2.9 KiB
Markdown
53 lines
2.9 KiB
Markdown
---
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layout: post
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title: Introducing PDPjs, a PDP-11 Emulator
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date: 2016-10-06 15:00:00
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permalink: /blog/2016/10/06/
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machines:
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- id: test1170
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type: pdp11
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debugger: true
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config: /devices/pdp11/machine/1170/vt100/debugger/machine.xml
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connection: dl11->vt100.serialPort
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- id: vt100
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type: pc8080
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config: /devices/pc8080/machine/vt100/machine.xml
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connection: serialPort->test1170.dl11
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---
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[PDPjs](/devices/pdp11/machine/) is the newest addition to the PCjs family of emulators, joining PCx86, PC8080, and C1Pjs.
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While PDPjs may eventually support a range of DEC PDP machines, my current focus is on the PDP-11, starting with the
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PDP-11/70. From there, I'll work backwards to support other PDP-11 models, such as the PDP-11/45, until I reach the
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beginning of the PDP-11 line: the PDP-11/20.
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I'm starting with the top-of-the-line PDP-11/70 largely because the core of the emulator is being adapted from the
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JavaScript [PDP-11/70 Emulator (v1.3)](http://skn.noip.me/pdp11/pdp11.html) written by
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Paul Nankervis, who has generously given permission to use his code in PCjs. Since his emulator is a fully functional
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11/70, it made sense to start there and work backwards, disabling features according to the model.
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The code has already undergone a lot of refactoring. Opcodes are now decoded by function tables rather than a single
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switch statement, and every opcode is implemented with a discrete function. Other refactoring includes flag management,
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interrupt management, and device management.
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Most of the work remaining is in device management. Like other PCjs emulators, PDPjs has a Bus component,
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[bus.js](/modules/pdp11/lib/bus.js), that allows separate device components to register I/O handlers for specific
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UNIBUS addresses. During the initial port, I moved all of Paul's original device management code into one "catch-all"
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component, [device.js](/modules/pdp11/lib/device.js), which has now been converted to the new I/O registration model.
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The first new device component is [serial.js](/modules/pdp11/lib/serial.js), which is currently the
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only means PDPjs has of communicating with the outside world. So you can try
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[PDPjs connected to a VT100 Terminal](/devices/pdp11/machine/1170/vt100/), by clicking the **Run** button on the
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test machine. The test machine is running a custom [Boot Monitor](/apps/pdp11/boot/monitor/) included with
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[Paul's emulator](http://skn.noip.me/pdp11/), but due to the lack of other device support, nothing can be booted yet.
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Obviously PDPjs is very much a work-in-progress. Before I proceed much farther, I really want to put the CPU through
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some rigorous testing, so I'll be on the lookout for some comprehensive PDP-11 instruction tests. Or I'll write my own,
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and compare results across 1 or 2 other PDP-11 emulators.
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{% include machine.html id="test1170" %}
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{% include machine.html id="vt100" %}
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*[@jeffpar](http://twitter.com/jeffpar)*
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*Oct 6, 2016*
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