SPI library does not have functions for sending or receiving data blocks

[eurol]

SPI library does not have functions for sending or receiving data blocks. SPI.transfer has disadvantages.

1. If I need to read from SPI a large block of data I often need to fill an array with a constant, f.e. 0xff
2. If I need to send data block to SPI several times I must fill this array again after each sending because it is filled with data read (that I don't need anyway)

I suggest to add functions like SPI.send(void* data, size_t len, unsigned char outbyte = 0xff) and SPI.receive(void* data, size_t len)

[PaulStoffregen]

If this is implemented, I hope the API will look like an overload of SPI.transfer(const void *wr, void *rd, size_t length) which has been discussed before, where NULL is supported for the 2nd input. When SPI.h supports this, SPI_HAS_TRANSFER_BUF should be defined.

For example, the Ethernet library already has support for using this, with cores having a SPI library with this feature. https://github.com/arduino-libraries/Ethernet/blob/master/src/utility/w5100.cpp#L316

[per1234]

This looks related to item (2): https://github.com/arduino/Arduino/pull/4573

[eurol]

Ok. Transferring can be done. But what should user do when he needs to receive a data block from a device that demands some value to continue data sending? For example device receives 0xff and continues to send data, but if it receives other byte value it stops?