WiFi + FPGA but not SPI interface

[Rob Young]

Scratching my head a bit and wondering about using WiFi as a port replacement for wired Ethernet with one of the Digilent FPGA boards such as CoraA7.

But the application in mind may need to be able to stream data at a rate higher than I believe I can push through an SPI port into one of the PMOD WiFi gizmos.  

 

So, here are my questions:

1) What is the highest sustained data rate one can push into a PMOD WiFi gizmo. Assume just filling up UDP packets with sampled data and maybe a bit of header info. 
2) What chip sets are viable that have an RMii type interface and would look (as closely as possible) like a wired connection?

Thanks for your thoughts and pointers on places to look.

[JColvin]

Hi @Rob Young,

Personally I would be more concerned about the data rate that the Pmod WiFi can achieve (with network traffic and software overhead) rather than the rate at which the hardware can provide data through a Pmod port, as the latter can almost always be orders of magnitude faster. In theory an IEEE 802.11g complaint chip (like the one on the Pmod WiFi) can achieve data rates up to 54 Mbps (equates to 6.75 MBps), though in practice this throughput will be less, for example Resource Center for the Pmod WiFi shows 1 or 2 Mbps for transferring data over 400 meters; by how much depends on network speeds/interference and how quickly you are collecting the data to send out over UDP.

On the software side for the Pmod WiFi, it only communicates through SPI, so for our FPGAs we use Xilinx's soft core processor (Microblaze) to work with the WiFi software stack to communicate with the Pmod WiFi through AXI Quad SPI IP (Xilinx product guide on it here), and there is some limitation on how fast that soft core processor will be able to run the SPI protocol communicating with the Pmod WiFi, though I'm not certain what the exact impact is in this case.

I'm a little confused about your second question. RMII is designed for a physical interface rather than a wireless one, so they don't tend to be directly compatible (they even have different IEEE standards), so unless you find a module that does both (maybe some ESP32 modules do this) it won't be readily feasible. Also, what do you mean by "would look (as closely as possible) like a wired connection"? Do you mean visually look like it, physically in terms of connectivity, or internally with the software? Out of curiosity, why are you looking to do wireless connectivity rather than wired?

Thanks,
JColvin