The code was doing:
pinMode(slaveSelectPin, OUTPUT);
pinMode(slaveSelectPin, HIGH);

Second pinMode should be digitalWrite

Add SPI Buffer functions

A define was under a #ifdef that it should not have been

Merged in the SPI.transfer(buf, retbuf, cnt)  version.

Also merged in the SPI.transfer(buf, retbuf, cnt, event_responder) version that does DMA access.

Allow setMISO/setMOSI/setSCK - after begin

Made the SPI code work like the old stuff where you could set the miso/mosi/sck pins after the begin.

Some people actually used this for changing SPI on the fly to use multiple sets of pins

Enable Pins - can set more options

The current table code was setup that when we choose a specific pin for MOSI or Miso or SCK (or CS), that the only thing set at the time was the MUX value.

Well the old enable_pins that was called off of the enumlated register was setting the PORT_PCR_DSE option on pins 11 and 13...

So to fix it, I have the table, allow you to fully set the options for each pin.
Still have most all of them just setting the MUX, but do have pins 11 and 13 setting the PCR_DSE option to be compatible with old code.

SPI Transfer(buf, cnt) use FIFO 16 bit

Experiment with making the whole transfer of the buffer act like it is
to logically hold the CS pins for that whole transfer.  This removes
gaps between each 16 bit transfer.

Update SPI.transfer(buf, cnt) to use the FIFO queue to speed things up.
It also speeds things up to pack the data into 16 bit transfers instead
of 8 bits.

As this code is more complicated,  no longer makes sense to inline it,
so functions moved from .h to .cpp files.

SPI1 and SPI2 transfer functions were updated as well for T3.5 and T3.6

Pin 45 is valid CS for SPI0 on new boards

USE SDCard pins for SPI1

This adds support for optionally being able to use the SDCard pins for
SPI1.

This change requires the corresponding changes in the CORES project

Add extern for SPI2 for T3.6

Beta boards changed names

SPI2 Support

Added SPI2 support for T34/T35 boards

Oops - missed debug message

Commented out other debug messages earlier, but missed this one

A serial debug line should be commented.

Added SPI1 object for Teensy 3.5 test board

These changes plus some changes in core (added register defines, plus
added logical SPCR1 register), allowed me to do quick hack to
serialFlash library and test and initialize flash memory using 3.5 test
board connected to prop shield using pins 0, 1, 20 and 6

Update SPI.h

In the comments: "Teensy 3.x" changed to "Teensy LC". Or is the LC also part of the "3" family?