Feature: Embedded
Instant-on machines don’t require installing a complex operating system before use, and don’t have to boot into that operating system from memory every time they are turned on or reset
control ports, also lacks any notion of imminence. Microcontroller boards such as Arduino, on the other hand, aren’t self-contained systems. T ey do not generate their own video, have no keyboard port whereby commands can be directly typed in, and can’t even compile or interpret the very sketches they run. To do all that, they need to be connected to a host PC, which itself lacks imminence. As a result, to this day we lack an instant-on, bare metal, self- contained control system programmed with the imminence of interpreted commands; something closer to my early vision of a “super ZX80” as a universal control panel. It is this gap that motivated me to develop the very system my child self always wanted to have.
A new kid on the block In the 40 years between 1981 and 2021, my life has taken me to computer engineering school, 25 years of professional experience
in the semiconductor industry, a couple of doctorates (one in computer engineering) and, more recently, semi-retirement from the technology sector. Having not yet turned 50, life has thus presented me with a rare combination of freedoms: more time to do what I fi nd cool, plus the knowledge, resources, energy and lucidity required to do it. Hence, Agon light was born; see Figures 2-4. It embodies a combination of instant-on single board computer
(SBC) and a self-contained microcontroller. It runs an extended incarnation of Acorn’s classic BBC BASIC on a modern version of the good, old Z80 microprocessor, used in all Sinclair machines. Like the microcomputers of old, it generates its own video and has its own keyboard input. But like modern microcontrollers, it also has 20 GPIOs (including a UART), SPI, I2C, system clock output, and two power rails (5V and 3.3V) available in its control port. All these control resources can be driven from the imminence and convenience of an interpreted BASIC prompt. Agon truly is the machine I always wanted to have. T e echoes of retro technology in Agon don’t stop here. Its very
architecture takes more than just a hint from the classical system partitioning between CPU and terminal. Agon’s CPU subsystem features an 8-bit eZ80F92 microcontroller, with a 3-stage pipeline and running at 18.432MHz, and 512KB of parallel system memory (10ns SRAM), a µSD-card port for mass storage, a ZDI interface for programming the eZ80’s basic operating system (called Quark MOS, written by Dean Belfield with contributions by Jeroen Venema), plus the control port itself and an ACCESS.bus header. Agon’s terminal subsystem comprises a triple-core ESP32- PICO-D4 running at 240MHz, plus 8MB of terminal memory
Figure 3: Block diagram of Agon light
www.electronicsworld.co.uk December/January 2023 21
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