Teensy 4.1 number of SPI ports

There are 3 on both t4 and t4.1. But 3rd on sd pins and on T41 on bottom memory chip pins
 
There are 3 on both t4 and t4.1. But 3rd on sd pins and on T41 on bottom memory chip pins

Would I be able to solder on a surface mount 0.05" header to connect an SPI peripheral or is it reserved somehow for QSPI memory chips?
 
Yes you can connect to those pins, not sure about any specific header for it. But if you find one that works...

I experimented using a few breakout boards and did a quick and dirty castellated extension board to play with those pins.
screenshot.jpg

A few caveats, you can use these pins for QSPI or other stuff, but not both. That is you have a PSRAM in one, then it uses up all of the pins (except one which is the Chip select for the other slot).

And the startup code will ping the QSPI to see if there is a PSRAM, which never interfered with what I tested.

And the QSPI pins and subsystem for spi are different than the SPI2 pins (Low Power SPI)....
 
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