patricklaf

Add SPI slave mode support

1

**Summary** This PR implements SPI slave mode for the SPI library. There is an existing PR, #1612, but it is not actively developped and it uses HAL and LL functions...

Fix for issue #85

**Description** The `peek()` functions of the `EthernetUDP` and `EthernetClient` classes always returns the first byte of a packet. A fix is proposed. **To Reproduce** Code used: ```cpp #include "Arduino.h" #include...