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Fri 31 December 2021
This year I've built a 16-bit CPU, along with custom operating system and programming language. It runs at 1 MHz and has 64 KWords of memory. This December I used it to do Advent of Code. Read more »
Thu 2 September 2021
All of the SCAMP hardware is now mounted properly inside the case, with no Arduino or breadboard required. I'm now well into the "long tail" of tasks on this project, where it takes increasingly large amounts of time to produce increasingly small improvements. Read more »
Mon 9 August 2021
Today I ported the SCAMP emulator to the web, using emscripten to compile C to WebAssembly, and Xterm.js to provide the terminal emulator. Read more »
Fri 6 August 2021
That's right! 1968's most exciting video game release is coming to 2021's most disappointing CPU architecture. Hamurabi is a single-player text-based game in which you play the leader of ancient Sumeria for 10 years. Each year, you decide how much land to buy or sell, how much food to feed to the population, and how much land to plant with seeds. Occasionally a plague comes along and kills half the population, or rats eat some of the harvest. Land values, harvest yields, and immigration rates fluctuate unpredictably. At the end of the 10 years (if you haven't been forcibly removed from office already) your performance is evaluated. Read more »
Thu 24 June 2021
I've made a bit more progress on my SCAMP CPU. I/O performance is improved significantly since last time, the CompactFlash card now lives on a PCB instead of a breadboard, I'm using a real (ish) serial console instead of an FTDI cable, and I have a more permanent power supply instead of the bench power supply. Read more »
Sat 29 May 2021
Thanks to Rory's suggestion of CD4504 TTL-to-CMOS level shifters, last night I finally succeeded in moving the CompactFlash glue logic out of the Arduino and into physical hardware. Read more »
Sun 25 April 2021
I reached another good milestone on SCAMP this week: the physical hardware booted all the way up to the shell. Granted, it only happened once, and I couldn't type any input once it got there. But it suggests that there are no fundamental problems with the hardware design that will prevent the computer from working, which I am very happy about. Read more »
Sat 3 April 2021
Thanks to the excellent Build Your Own Text Editor tutorial, SCAMP/os now has an editor. It's pretty bare-bones, but perfect for what I need. Read more »
Sun 21 March 2021
I have reached a good milestone on the SCAMP hardware: it can now execute code! It runs all the way through the test program correctly. Read more »
Sun 28 February 2021
I've put together the memory card for the SCAMP CPU, including the front panel with LEDs to show the bus contents and address register. Read more »
Sat 27 February 2021
You might think it's a bit early to be working on an operating system, given that I don't have a CPU to run it on. Maybe you're right. But working on software is easy and working on hardware is time-consuming, so here we are. Read more »
Fri 19 February 2021
I've been working on a compiler for the SCAMP CPU. It compiles a language I'm calling "SLANG" (which just stands for "SCAMP Language" pending a better backronym) into SCAMP assembly language. Read more »
Mon 15 February 2021
The day after my first attempt at milling a PCB, my new tooling arrived (a 1 mm drill bit and a 10° engraving tool), so I had another go at making a PCB. Read more »
Fri 12 February 2021
I'm going to get most of the PCBs for SCAMP made by JLCPCB, but I'd like to try to mill the backplane on the CNC machine because it is both large (expensive at JLCPCB) and simple (single-sided, no vias, easy to make). Yesterday some small pieces of copper-clad board arrived and today I had a first attempt to see what would go wrong. Read more »
Sat 6 February 2021
I'm pretty happy with the CPU design now and am ready to proceed to making it physically exist. I am still finding the odd microcode bug, but these can be fixed at any time. I'm at least not finding any architecture-level bugs. Read more »
Sun 31 January 2021
I (believe I) am making good progress on designing the TTL CPU. Most of the actual CPU design is relatively stable now, and bug discoveries in the hardware design are infrequent, so now I get to move up a level and work on the instruction set. After that, it's just the bootloader, operating system, and application software. Oh, and the small matter of the physical hardware assembly... Read more »
Sun 24 January 2021
I want to make a CPU out of physical 74xx TTL chips. I have now implemented most of the parts using a subset of Verilog that maps directly to TTL chips, and I wanted to write a bit about the design. Read more »
Fri 15 January 2021
On Graham's recommendation, I recently bought an iCE40 FPGA and have been learning a bit about how to use it. The iCE40 is good to get because there is good open-source tooling that supports it. I was originally going to get the iCEstick evaluation board, but there are other alternatives available more cheaply and with more logic elements. I ended up getting an iceFun and have found it to be quite easy to use. The example projects are helpful. Read more »