Why Your Amstrad CPC Might Crash in 2104!
Recently I was reading the source code of the firmware routine which updates the system TIME in the Amstrad CPC. This code contains a bug which will eventually crash your machine! Read on for the full gory details! Updating the Timer The TIME counter is a is 32-bit wide integer (four bytes) which is updated …. Read More
Writing a Compiler 1: Expressions and Intermediate Language
Recently I’ve been getting increasingly broody to write a compiler. They’ve always been something of a mystery to me and, while I’ve always fancied writing one, I’ve never had a convincing reason to do so. But, since I’ve returned to retro computing, I can see definite limitations in the options currently available for writing software …. Read More
Passing Code Pointers as Data in Amstrad CPC BASIC
One of my secret coding pleasures is passing a function as a parameter to a subroutine. Most modern languages have what’s called ‘first class code’. That means that you can assign the address of a function to a variable, store it in an array, and pass it as a parameter to a function. This enables …. Read More
How Amstrad CPC BASIC Compresses Error Messages
Amstrad CPC BASIC saves a few bytes by using some interesting compression in the way it stores error messages. Let’s take a look at how it works and how much space it saves. Below is the table of error messages. The messages are stored in what I refer to as ASCII7 format – bit 7 …. Read More
Comparing Datapoint 2200, 8008, 8080 and Z80 Instruction Sets
Before Intel created the 8080 it designed the 8008, the first eight bit microprocessor, and the first microprocessor to go on general sale. The 8008 was designed as a single chip version of the TTL processor in the Datapoint 2200, itself the first desktop computer. I’ve long known that the Datapoint 2200 had a very …. Read More
My RetroChallenge 2021/10 Project – Amstrad CPC Firmware
My entry for RetroChallenge 2021/10 is to publish reverse engineered versions of the Amstrad CPC firmware ROMs which can be modified and assembled. In this post I want to explain why why I’m doing this. The first reason is a personal one: I have several projects on the go which would benefit from this. The …. Read More
Understanding the Amstrad CPC Video, RAM and Gate Array Subsystem
The Amstrad CPC is my favourite 8-bit home computer system – I still have my childhood CPC464. There are a number of things I love about it’s design, including the video system, which offers higher resolution and a larger colour palette than most of it’s siblings. Recently I’ve put some effort into understanding how the …. Read More