Switch to using Arduino SPI library

[njh]

Switch from manipulating the AVR registers directly to using the Arduino SPI library.

• Should allows EtherCard to work on other architectures
• Compile size is a little bit smaller
• Cleaner code

Note there is a little bit more work to do on this, please don't merge yet.

Before merging, it would be really good if people were able to test out this branch and see if it works for them on a variety of Arduino boards.

[SomeshDaga]

@njh It's still seems to be looking for avr/eeprom.h library that is not found for non-avr microcontrollers.

Tested it on a Arduino Due where compilation failed when it couldn't find the above.

[jamesfowkes]

I have tried this pull request with the new Arduino Nano Every.

The SPI works fine though I had to add support for checking if the SPI peripheral was enabled:

if ((SPI0.CTRLA & SPI_ENABLE_bm) == 0)
    initSPI();

In addition, the library seems to be processing each HTTP request three times. If I use curl to make a request, e.g.:

curl -i http://192.168.0.25/tare

my application code sees and handles three of them. This is three consecutive log lines from my application's HTTP handler, which calls ether.packetReceive() and ether.packetLoop()

APP: Handling URL /tare
APP: Handling URL /tare
APP: Handling URL /tare

So the handler is getting a positive value from ether.packetLoop() three times per actual request. This is consistent behaviour over multiple requests. I haven't determined if this is related to the SPI changes or something else.

[jamesfowkes]

I can also confirm that the behaviour I described above occurs under certain conditions with a normal Arduino Nano - I haven't worked out what those conditions are yet.

[mirh]

I did also try on a Nano Every, but even with the extra tweak above I'm hitting a wall with

EtherCard/src/bufferfiller.cpp

Line 62 in 713e9b0

while ((d = eeprom_read_byte(s++)) != 0)