Quick question about SPI

so the story is really short , you can set the speed of the spi bus
but when writing a byte you must wait until the flag indicates that the byte is sent .
can i know exactly how long it takes for the byte to be sent ? (for time sensitive apps?)

can i know exactly how long it takes for the byte to be sent ?

You could measure it. I suspect it would be a bit like trying to measure the speed of light with a yardstick and a calendar, though.

yh hhh exactly , i did try to measure it , and the measurement is not accurate at all since debugging the result requires at least 100ms or more for a human to detect the result while the accuracy i need is less than 3us . i did try to initiate a timer to count from beguinning to end , but detecting the end takes time so there is a time waste there to

You don't have to wait. You just need to ensure that you don't write another byte to the SPI data register before the first one has been transmitted.

You may get good approximation t = 8 / SPI(bps). For example, running spi at 8MHz, byte is sent in 1 us.

thank you very much guys , karma given