SPI WIFI passthrough

Kiran Rajmohan
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Joined: Sun Aug 13, 2017 1:30 am

SPI WIFI passthrough

Postby Kiran Rajmohan » Sun Aug 13, 2017 5:20 am

I am trying to figure out how to use the SPI-WIFI passthrough mode. I noticed this in the technical manual https://espressif.com/sites/default/fil ... nce_en.pdf . However, I have not seen anyone use it or even mention it anywhere other than on this manual.

Is this mode functional and usable? The sections 6 & 7 mentions some signal lines which I have not been able to figure out.

This protocol uses the ESP8266 slave mode to communicate with other processor's SPI master. Signal line No.5 is used to implement this protocol. Apart from signal line No.4 needed for standard SPI, signal line No.1 is also needed to inform the master of the update of the slave status register.


What are these signal lines mentioned?

I have seen lots of projects using the ESP8266 as a UART-WIFI passthrough device. I was hoping that the SPI passthrough could yield a higher throughput. Is this a correct assumption? I am planning to use an ESP-12E device.

Any insights into this would be greatly appreciated. :)

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pratik
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Re: SPI WIFI passthrough

Postby pratik » Fri Aug 25, 2017 7:14 pm

The ESP8266 SPI slave uses the SDIO slave, which is unfortunately sharing pins with the SPI flash chip.
So to get the AT firmware with passthrough up and running, what you need to do is:
1. Have ESP8266 with flash on HSPI interface (as in ESP-WROOM-S2, not in regular ESP modules that runs user code).
2. Program HSPI flash with AT firmware.
3. Boot ESP in SDIO mode (not flash mode or UARt programming mode).
4. Make the SDIO host configure ESP to execute from HSPI flash address.
5. Then you have SPI slave mode.

The pain is not worth it, there are thousands of lines of code involved. I just program the HSPI slave module + custom AT commands to get 8 mbps throughput on wireless communication using regular AT commands.
Example of SDIO slave driver:
https://github.com/al177/esp8089
Regards,
Pratik Panda
Website: http://www.PratikPanda.com

Custom firmware, Knowledge base and freelancing (ESP8266/ESP32):
http://www.iot-bits.com

Kiran Rajmohan
Posts: 2
Joined: Sun Aug 13, 2017 1:30 am

Re: SPI WIFI passthrough

Postby Kiran Rajmohan » Fri Aug 25, 2017 7:22 pm

Now, it makes sense that not many are talking about it. Thank you for the clarification. I'm curious about the configuration in which you are getting the 8 mbps throughput. Do you have some codes you could share for achieving this throughput.

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pratik
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Re: SPI WIFI passthrough

Postby pratik » Sun Aug 27, 2017 3:13 pm

It is developed by a third party I work with sometimes. Not sure if it can be released. I will update the thread if it can be put out.
Regards,
Pratik Panda
Website: http://www.PratikPanda.com

Custom firmware, Knowledge base and freelancing (ESP8266/ESP32):
http://www.iot-bits.com

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