how fast can spi_xfer() send?

Honken · Joined: 03 Mar 2004 Posts: 15

What is the maximum speed that spi_xfer() function can send a byte?

I have a MCU running @ 96 Mhz, and can only get up to 1.2 Mbit when I declare baudrate to be 1500000 in #spi setup.

Ttelmah · Guest

Start with what CPU?.
Now, the SPI setup, will always tend to select the fastest available transfer _below_ your selection. Now, the available selections, will depend on the dividers available on your CPU. Hence the first question...
In most cases for the faster CPU's, the dividers have a first prescaler, that is 1:4,16,64, then a 1:1,2,3,4,5,6,7,8 prescaler after this. So, for a 96MHz source, the /4 prescaler, won't get to this, so the /16 prescaler will have to be selected, giving 6MHz to the second prescaler. The compiler should then select /4, to give 1.5Mhz.
The 'maximum speed', should be way higher than this. There is normally a maximum around 10MHz.
Are you sure you are using the hardware pins?. The maximum for software SPI, is well below the available hardware rates
Try just raising the requested rate slightly.

Best Wishes