Fast SPI-USART (SPI-UART) for Arduino/Nano (ATmega328p) and special support for LGT8F MCU
Very fast replacement for SPI.h using the USART as SPI.
This code can keep up a constant SPI clock without interruptions at fastest (half of system) clock (16MHz MCU = 8MHz SPI, 32MHz MCU = 16MHz SPI) in its transfer(buffer[,buffer],count) functions. The default SPI libraries are not capable of this, as the USART has a ONE byte buffer, the ATmega328p-SPI has none. With this single byte buffer you get much faster transfers using SPI_UART. Though the code was written with the LGT8F in mind, it now also works on the "slower" (more cpu cycles per instruction) 328p.
Special support for LGT8F MCUs: Allows remapping RXD/TXD (MISO/MOSI) from pins D0/D1 to D5/D6 for "parallel" usage of serial interface, SPI and USART SPI on different pins. Playing with the big ones ^^
Now, if all those libraries in the wild would ever think of not using a hardcoded SPI.. There are even MCUs with 2 and more hardware SPI out there...
Please read SPI_UART.h
Remark: I used SPI_UART naming, despite it should be SPI_USART, to be able to use it with the nRF24 library.
Set the pin mode before begin() for LGT8F mcu:
useAlternatePins=false: RXD =MISO=D0, TXD =MOSI=D1useAlternatePins=true: RXD*=MISO=D5, TXD*=MOSI=D6
The CLOCK always is XCK=SCK=D4. We do NOT have an SS line, as USART only support master mode.
You can NOT use the Serial in parallel using SPI_UART, but you may switch between using Serial.begin+Serial.end and SPI_UART.begin/SPI_UART.end, if you are on LGT8F with alternate pin sets.