tom dunigan

Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

7 years, 11 months ago.

Why are SPI data rates slower?

On 11/9/15 a simple SPI transfer loop of 1024 bytes for various SPI speeds ran as follows

      spi 1 mhz 5963 us 1.37 mbs  36c
      spi 2 mhz 5963 us 1.37 mbs  36c
      spi 4 mhz 3233 us 2.53 mbs  364
      spi 8 mhz 1868 us 4.39 mbs  35c
      spi 15 mhz 1184 us 6.92 mbs  354
      spi 30 mhz 844 us 9.71 mbs  34c
      spi 45 mhz 706 us 11.60 mbs  344

Today, SPI is much slower
         spi 1 mhz 13626 us 0.60 mbs  374
         spi 2 mhz 8133 us 1.01 mbs  36c
         spi 4 mhz 5511 us 1.49 mbs  364
         spi 8 mhz 3943 us 2.08 mbs  35c
         spi 15 mhz 3418 us 2.40 mbs  354
         spi 30 mhz 2896 us 2.83 mbs  34c
         spi 45 mhz 2895 us 2.83 mbs  344

The SPI-DMA rate is still good using /2 scaler, i can get 44.3 mbs (megabits/sec)

Question relating to:

Last updated: 15 Mar 2022
Affordable and flexible platform to ease prototyping using a STM32F446RET6 microcontroller.

1 Answer

Guillaume F4HDK
7 years, 10 months ago.

It seems that we have similar problems : https://developer.mbed.org/questions/76888/SPItransfer-Master-is-slow-on-Nucleo-L43/

Could you please explain this?

"The SPI-DMA rate is still good using /2 scaler, i can get 44.3 mbs (megabits/sec)"