Pcjr on RETRO.MOE

64K RAM Ought to be Enough: a demo for the PCjr

Thu, 27 Sep 2018 06:25:17 +0000

Updated 2018–10–08

A demo for the IBM PCjr by Pungas de Villa Martelli. It was presented at Flashparty 2018 and won the Demo category.

Requirements

An IBM PCjr with at least 64k RAM.

Download

Source code: https://github.com/ricardoquesada/64k-ought-to-be-enough
Binary: pvm-64ko.zip (does not run on emulators)

Technical description

The demo is divided in the boot loader and demo 3 parts

Performance of the 8088 on PC, PCjr and Tandy 1000

Mon, 05 Mar 2018 05:34:26 +0000

It’s well-known that you should measure the performance of your code, and not rely only on the opcode’s “cycle counts”.

But how fast is an IBM PC 5150 compared to a PCjr ? or to a Tandy 1000? or how fast is the Tandy 1000 HX in fast mode (7.16Mhz) compared to the slow mode ( 4.77Mhz) ? Or how fast is a nop compared to a cwd ?

I created a test ( perf.asm) that measures the performance of different opcodes and run it on different Intel 8088 machines. I run the test multiple times just to make sure the results were stable enough. All interrupts were disabled, except the Timer (of course). And on the PCjr the NMI is disabled as well.

IBM PCjr BIOS dump

Wed, 03 Jan 2018 15:29:57 +0000

The IBM PCjr BIOS is very well documented in the IBM PCjr Technical Reference manual (a must read for every PCjr developer).

The only problem is that navigating that code is not easy. It has all the problems from scanned books:

the fonts don’t look good
no hyper-links
and difficult to search

So I dumped the BIOS and started analyzing it with IDA Pro 5.0 - Free version. I added some of the original comments from the Technical Reference manual, and added some comments of my own.

Tandy 64 Jr. - an intro for the IBM PCjr

Wed, 03 Jan 2018 02:19:51 +0000

Happy new year!

We (PVM) ported our Tandy 64 intro (originally designed for the Tandy 1000HX) to the IBM PCjr.

Requirements: IBM PCjr. with 256k RAM

Download:

Binary: tandy64jr.zip
Source code: https://github.com/c64scene-ar/tandy64/tree/ibm_pcjr

Worth mentioning:

Runs flicker-free
Stable raster-bar, without garbage (world-first?)