Appendix C – Machine Personalities

Overview

Your ZX Spectrum Next computer is unique in the fact that unlike other computers that emulate older machines using software, it changes its actual hardware to reflect the hardware of an older ZX Spectrum model. This fact, is what allows it to achieve almost 100% compatibility with older models whereas even a ZX Spectrum 128K for example couldn't run a lot of software originally made for the 48K.

The technology that makes all this possible is contained within a very large reconfigurable logic device called a Field Programmable Gate Array (FPGA).

For all purposes, once your ZX Spectrum Next goes into an older ZX Spectrum model personality, it's almost identical to that model internally. Moreover, since FPGAs can be made into almost any conceivable kind of digital circuit using a Hardware Description Language (HDL), your ZX Spectrum Next can become other machines using different CPU models; this is what we call multicore capability.

Before we examine what machine personalities are available on the ZX Spectrum Next, it is a good idea to start with learning about how to update the machine's core(s), firmware and system software.

The Cores and their update procedures

The ZX Spectrum Next is primarily a ZX Spectrum computer; its main core will always be one of a ZX Spectrum compatible machine (albeit with many extra features) however since it is also a multicore machine, it has two separate (but very similar) procedures to update its main core and a third one for additional cores¹.

Let us first clarify a few things about what a core is and what it isn't. A core is a bitstream written in an HDL, "compiled" for the specific models of Xilinx™ FPGA the ZX Spectrum Next Issues 2 and 4 use and stored onboard a serial flash rom IC on the ZX Spectrum Next board. It contains all the logic that allows the FPGA device to reconfigure itself into the individual components that make up a ZX Spectrum Next. Every time you turn on your ZX Spectrum Next the core gets tranferred to the FPGA almost instantaneously. It doesn't get etched permanently inside the FPGA; instead the FPGA is empty every time the computer gets powered up.

We may be talking about one ZX Spectrum Next core but in reality due to the two production mainboards in existence (each with a different model of a Xilinx-brand FPGA), there are four; there are two Anti Brick cores (AB) and two regular cores you get with every new System/Next™ update. The AB cores serve two purposes: The main is to perform the inital machine startup and the secondary is to protect you from a botched attempt to flash a new core into the system's flash rom (hence the name Anti Brick²).

Every time the computer starts it transfers the AB core onto the FPGA, then the AB core loads the Firmware file from the root folder of the System/Next™ distribution and that in turn loads the regular core into the FPGA, then loads the appropriate configuration and finally starts the machine.

The AB core does not get updated; only the regular core is. The AB core needs a special procedure which is done at the factory to get updated so it won't be covered here.

There are two methods of updating the regular core; the first one is the normal one, and the one you should use while the second one is reserved only if told so by the release

¹ SpecNext Ltd does not offer additional cores at the time of writing; 3rd party cores are the responsibility of their respective authors ²: Bricking is a term used for a failed update in digital electronics that leaves a device unusable; in other words unmovable as a "brick".