On the board microzed sd card work very slow.

Hi all! I'm set microSD card transcend (UHS-I) in microzed board with cristall zynq 7Z020. I'm used functions from diskio.c: stat = disk_read(0, rx_buf, i,32);

That is, in a cycle reads the 32 data blocks 512 MB:

while(1){

stat = disk_read(0, rx_buf, i,32);

}

The reading speed is less than 40 Mbits per second which is very slow.

Why such a low speed and how it can be raised?

0 narrucmot over 8 years ago

Because not all SD cards are created equally, and many can't operate at maximum speed, we deliberately limit the SD card clock to 25MHz in the Zynq PS configuration. This allows for maximum capability with the side varierty of SD cards that our customers may be using. If you are confident your particular SD card will operate at a faster SD clock, you are welcome to modify the SD clock to a higher frequency. This may take some experimentation to achieve the data rate to mee your requirements.
--Tom
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0 bhfletcher over 8 years ago

Have you looked at this article?
http://zedboard.org/content/sd-card-advice-zynq-7000-soc-products-0

Also, what Vivado version? We've heard of a known issue in 2016.2 that affects SD Card speed. If you are using 2016.2, then you should open a support case with Xilinx or use their forums to request more information.

Bryan
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0 Former Member over 8 years ago

Thank you narrucmot, fletch.
I'm works in vivado 2016.1.
If in this function: stat = disk_read(0, rx_buf, i,32); read not for 32 units, but, for example, 1000 units, then the read speed increases to ~ 20Mbytes per second.
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0 Former Member over 8 years ago

It also should be noted that the microzed board uses a translater to communicate with the card at 3.3V. The UHS-I specification requires the card to switch to 1.8V to achieve anything faster than Default Speed (25Mhz) and High Speed (50Mhz)so your effective throughput would be limited to 25Mbytes.
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0 bhfletcher over 8 years ago

The Zynq SDIO controller max clock rate is 50 MHz, so higher than that is not an option even if 1.8V was supported.
Bryan
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0 kilrill over 8 years ago

So if the card is fast enough, no, it won't slow the phone down, since the only time the phone looks at the card is during the initial media scan and any time you access a data file from the card.
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