[Cryptech Core] Xilinx Zync devices for possible next Cryptech HSM

[Joachim Strömbergson]

Aloha

(wall of text again)

On the latest f2f I presented possible ways of improving the Alpha board
with minor or major changes. One of the major changes (i.e. a new board)
presented was to replace the MCU and the FPGA with a device that
incorporates both a CPU platform and a FPGA fabric in a single die. For
example the Xilinx Zync-7000 devices [1]. For Xilinx Zync selection
guide see [2]. For comparison to other Xilinx generation 7 devices see
[3]. For all Zync devices available from Digijey, please see [4].

The much higher clock speed of the integrated ARM cores, low latency
on-chip memory and esp wide, low latency interfaces between the CPU and
FPGA would allow very much higher performance than what we can reach on
the current Alpha board. (The maximum clock frequency of the cores in
the FPGA would not increase substantially.)

One thing we talked about was the increase in price for Zync vs Artix. I
promised to check device prices.

To have something to compare with, the current Alpha board use a Artix-7
200T device packaged in a 484 ball BGA. The device provides:

215k Logic cells
269k Registers
365  BlockRAMs

The unit price is something like 222 USD for industrial rated devices
and 194 for commercially rated devices. The Alpha board also has a
STM32F429 MCU, which cost around 16 USD in low volume.

As of current FPGA configuration we use something like 30% of the
resources in the FPGA.


The Zync device that provides at least the same amount of resources as
the current FPGA is XC7Z035. It is based on Kintex-7 and sports:
275k Logic cells
343k Registers
500  BlockRAMs

That is about 30% - 40% more resources compared to the device used on
the Alpha today. The cheapest device is a commercially rated -1 speed
grade device in 676 BGA package. The low volume price is 952 USD. That
device sports a dual core ARM Cortex-A9MP CPU running at 667 MHz.

Unfortunately, the next device down in terms of resources is the
XC7Z030. This is also a Kintex-7 based device and it provides:
125k Logic cells
157k Registers
256  BlockRAM

A large step down from the resources provided by the XC7Z035, and a
fairly step down from what we have today. The price for this device is
however really good. In a 484 ball BGA (similar to what we have today),
the price is 209 USD.


In short: Using Zync and having at least the same amount of headroom in
the FPGA would bump the BOM cost something like 4x, but we would then
have much more headroom. And substantial performance boost. If we could
handle less headroom than today, we could use a Zync XC7Z030 device that
would reduce BOM cost, and also improve performance quite significantly.	



References:
-----------
[1] Xilinx Zync-7000 product page:
https://www.xilinx.com/products/silicon-devices/soc/zynq-7000.html


[2] Xilinx device selection guide for Zync-7000:
https://www.xilinx.com/support/documentation/selection-guides/zynq-7000-product-selection-guide.pdf


[3] Xilinx 7 series FPGAs on which the FPGA part of the Zync devices are
based on. For example the Artix-7:
https://www.xilinx.com/support/documentation/selection-guides/7-series-product-selection-guide.pdf


[4] All Zync-7000 devices available from Digikey:
https://www.digikey.com/products/en/integrated-circuits-ics/embedded-system-on-chip-soc/777?k=XC7Z

-- 
Med vänlig hälsning, Yours

Joachim Strömbergson
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                               Assured AB
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