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BBB using SPI with Microchip 25LC512 flash

Former Member

As a learning experience, I got an SPI flash chip (25LC512) working with my BBB. I thought the steps I went through and performance observed could be useful to others, so I wrote a blog post about the details at:http://www.zephyr-labs.com/?p=139 with links to the git repo for code and performance traces from my Saleae logic analyzer (wonderful tool). Synopsis:

SPI through libsoc library can issue commands every ~100 usec (observed between 77 and 125 usec). Random 1 byte reads can complete every ~100 usec as well. 128 bytes can be transferred from the BBB to/from the 25LC512 in ~200 usec. A long block of sequential reads run at about 640 KB/s

  • performance is quite poor, the SPI dtbo includes 

    spi-max-frequency = <16000000>;

    which is a clock rate of 16MHz, so assuming 8 bits per 'byte' you should theoretically be able to clock data over the SPI connection at approx 2MB/s as you can generally clock in a start address then keep reading sequentially.

     

    Your analyser trace is interesting as it appears to have about a 1 byte gap between each burst on the clock. Lots of room for improvement there. An interesting excercise would be to determine if this latency is caused by the lib you're using, by the BBB's spi driver, or is inherent in devspi.