Writing a Compiler 3: The Branch Fixup
I left the last article by talking about a bug. Look at this source code: and the IL which is being generated from it: Assignments to a variable are versioned. I.e. every variable reference has a ‘subscript’, which is incremented for every write. So in this example we have %a_0, %a_1, and %a_2, all of …. Read More
Writing a Compiler 2: Conditionals
In part one I showed how my compiler is parsing expressions and converting this into an intermediate language format suitable for optimisation and code generation. The code in part one was purely linear with no branches or loops. In this second article I begin to deal with code which has multiple execution paths. I’ll start …. 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
Designing an Intel 8008 Computer. Part 1: Power, Clocks and Signals
The Intel 8008 was the second microprocessor, and the first 8-bit one, as well as being the first microprocessor to go on general sale. It’s an interesting and quirky beast which was constrained by bleeding edge technology and a curious edict from the Intel management. In terms of history, the 8008 was designed under contract …. 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
Variables, DEF FN Definitions and Arrays Storage in Amstrad CPC/Locomotive BASIC
(The information in this article comes from reverse engineering Amstrad CPC BASIC. You can find the reverse engineered source code in my CPC BASIC source code repository. You can find an example BASIC program which ‘walks’ the storage areas in the Examples folder of that repository. See also the CPC Wiki page for more technical …. 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