What would be faster? SHIFTOUT or Soft SPI ?

acjacques · Joined: 24 Feb 2019 Posts: 10 Location: Rio de Janeiro

What would be faster? SHIFTOUT/SHIFTIN or Software SPI ?

Processor is AtMega 328P @ 16Mhz

(BASCOM-AVR version : 2.0.8.1 )

Paulvk · Joined: 28 Jul 2006 Posts: 1121 Location: SYDNEY

What do you want to drive with this?

MWS · Joined: 22 Aug 2009 Posts: 1722

Hard-SPI with its SCK of fOsc/2 is faster, likely there won't be a difference between the Soft-versions.
Overall speed is a function of serial IO and code to fetch or store corresponding data, while the latter can take up multiple times of the transfer. SPI still has advantages, as the integrated SPI unit does rx/tx on its own, while user code can do other stuff in the meantime.
At fastest pace with Hard-SPI one byte takes 16 cpu clocks, If storing of data takes for example 100 cpu cycles, overall speed is rather slow.