ESP32 Forum

I would like to send signals from all SPIs at exact time so I know when all transmissions end at same time
Are they synchronized by default or must be configured?

I also noticed there are special functions for SPI pins as output:

(gpio_sig_map.h)

So f.ex. code - gpio_matrix_out(MY_PIN, SPID4_OUT_IDX, 0, 0)
will map my MY_PIN to first bit of SPI data?
What are those signals for SPI functions and how does that work?

Thanks

I suspect this is an 'X-Y' problem; therefore what are you trying to do that requires synchronised SPI exchanges?
You *might* be able to do something like:
- make one SPI module the master and all others slaves
- the master will generate the SCK signal and all others will use that
- because SPI is an exchange process, if you connect pairs of SPI modules together in the usual manner (output of one to the input of the other) but configure both as slaves, then both will respond the to the master clock at the same time and so both will try to send and receive at the same time and so still exchange their values.
- All of the slaves could share the \CS\ line
I've certainly not tried this but, there again, I can't think of a situation where I'd want to synchronise multiple SPI exchanges.
Susan

Thanks Susan. It is complicated, I'm trying to synchronize 2 or more devices that should read data at exact time.
I will look for more solutions I think.
Looks like gpio_matrix_out can map bits 4-7 of SPI data byte to individual pins which may help if it works

Now I am more confused.
SPI is a serial exchange protocol which means that each bit of a value being sent is presented to the MOSI (for a master - MISO for a slave device) pin in line with the SCK transitions.
Therefore I have no idea how this relates to the gpio_matrix_out function.
You don't mention what the other devices are but if they all take the same 'command' value and all start reading data at exactly the same time (say at the end of the reception of the command data) then just tying all of the slave devices MOSI and \CS\ pins together would let them all receive the same command at the same time.
You would probably still need separate SPI modules to read in the results from each device - assuming they are all sent back via the SPI interface.
Susan

Aussie Susan wrote: SPI is a serial exchange protocol which means that each bit of a value being sent is presented to the MOSI (for a master - MISO for a slave device) pin in line with the SCK transitions.
Therefore I have no idea how this relates to the gpio_matrix_out function.

Yes but normally all bits go through one pin and I know other MCUs are capable of mapping sequence of bits/signals in a transmitted byte to the pins. Usually 8bits/8pins or 16/24/32. I wil try it when have more time but in case of esp32 that would be only half a byte per spi

Got it now - you are talking about Quad SPI (QSPI)
Susan