Xilinx-Artix-7 FPGA
FPGA Upgrade: Artix-7 vs Spartan-6
The ZX Spectrum Next Kickstarter model KS2 (Issue 4 board) uses the Xilinx Artix-7 XC7A15T FPGA, replacing the Xilinx Spartan-6 XC6SLX16 FPGA used in the original KS1 (Issue 2B board). The Artix-7 is a more modern device, offering better performance, lower power consumption, and access to newer development tools.
The KS3 will use an Artix-7 XC7A35T-2 which pretty much doubles the logic cells, block RAM and DSP slices.
Below is a comparison between the three FPGAs:
| Feature | Spartan-6 XC6SLX16 (KS1 - Issue 2B) | Artix-7 XC7A15T (KS2 - Issue 4) | Artix-7 XC7A35T-2 (KS3) |
|---|---|---|---|
| Technology Node | 45 nm | 28 nm | 28nm |
| Logic Cells | ~14,579 | ~16,640 | ~33,280 |
| Flip-Flops | 18,224 | 20,800 | 41,600 |
| Block RAM | 576 Kbits | 918 Kbits | 1,800 Kbits |
| DSP Slices | 32 | 45 | 90 |
| Power Consumption | Higher | Lower (static & dynamic) | Lower (static & dynamic) |
| Clock Management | PLL-based | MMCMs and PLLs (more flexible) | MMCMs and PLLs (more flexible) |
| Toolchain | Xilinx ISE (legacy) | Xilinx Vivado (modern) | Xilinx Vivado (modern) |
| Partial Reconfiguration | Not supported | Supported | Supported |
Although the Spartan and Artix FPGA models require different bitstreams due to the differing FPGA architectures, all systems are designed to remain feature-identical wherever possible in the Next Core to avoid splitting the user base. The KS2 and KS3 larger FPGA's could provide alternate cores with extra features - e.g. the Official QL core has Sprites on a KS2 to create an enhanced QL.
The only additions exclusive to KS2 (Issue 4) are four extra Category:Next Configuration Registers used for low-level hardware access:
- XDEV command ($F0) – XDEV CMD
- XADC register ($F8) – XADC REG
- XADC D0 ($F9) – XADC D0
- XADC D1 ($FA) – XADC D1
These registers allow developers to interact with internal Xilinx features such as the DNA ID and XADC (analog-to-digital converter). Technical documentation for these registers can be found on their respective pages.