Does it work for ESP8266 <-> ESP8266?

[haldark]

Hello Mr. Bilek,

This project seems very interesting to me. I am trying to run it from yesterday, but not successful.

My Arduino IDE is version is 1.8.13, and ESP8266 core is version 3.0.2

As I understand from the description, the slave code is to be run on ESP8266 microcontroller, and the Master code is to be run on 328p microcontroller.

What if I want to run the master code also on Arduino/ESP8266 or Arduino/RP2040 (Pico)? Will it work?

Another problem I faced is with GPIO15. For the slave code to run, it seems this is a hard requirement for ESP8266 to use GPIO15 as SS. May be GPIO15 is connected to internal hardware SPI circuit? But ESP8266 does not boot, or flash if that pin is not pulled low. When this pin is connected to a SPI master, the master pulls it high by default. So, every time I want to flash, or boot ESP8266, I have to disconnect the GPIO15 of ESP8266 from master. Is there any workaround for that?

Thanks a lot for making such a project. Appreciate if you can help me getting this up and running.

--Kish

[JiriBilek]

Hello,
it should work although I never haven't tested it. You have to connect correctly the SPI bus, I mean the MISO-MOSI pairs crossed.
The problem with GPIO15 is solved by an additional circuitry - see #6

[haldark]

Hello Mr. Bilek,

Really appreciated your reply.

I thought about crossed MOSI-MISO. Here are my thoughts.

GPIO13 is MOSI. Which means when in master mode, this pin is Master Data output (should be configured as output when I call SPI.begin(). When in Slave mode, this pin is Slave Data Input (should be configured as Input when I call Slave.begin(). Hence I should connect GPIO13 of master ESP8266 to GPIO13 of Slave ESP8266.

Does it make sense?

I am scared to experiment by connecting GPIO13(MOSI pin of master ESP8266) to GPIO12(MISO pin of slave ESP8266) as both would be configured as output and drive simultaneously to each other.

If I am making mistake in my reasoning, would appreciate if you can correct my course.

[haldark]

I am experiencing a strange thing. I am not able to get the ESP8266 example sketch of SPI_master to work.

I simply open the example sketch in the Arduino editor. The sketch name is SpiSlave_master.ino. I upload and run it on ESP8266. Then open the serial monitor at 115200 baud. I see that the sketch is printing "Master: Are you alive?". Anyway there is no slave connected, so I don't expect any slave messages to be printed. However when I monitor SCLK pin with my oscilloscope, I see no clock like activity. It is just a flat line. I also see that CS line is constantly high. This means that SPI master module is not actively driving the SPI bus.

But, examples that comes with ESP8266 core must be well tested. I wonder what I am doing wrong. Or rather, is there anything special I should do?

I am asking these to you since I believe you must have done lot of experiments during development of WifiSpiEsp. I wonder if you had used these example sketches and experienced the same hurdles.

Appreciate your wise advice.

[JiriBilek]

Hello,
you're right, there is no crossing MOSI/MISO signals, sorry.

The behaviour of the SPISlave_Master example is weird. It should at least pulse the SS line because this is done by digitalWrite function. In the days I experimented with SPI on 8266 I ran these examples without a problem.

[JAndrassy]

in master use some other pin than 15 for CS. try io 5