task not relinquishing scheduler busy waiting..

Mr. Andrei Chichak groups at chichak.ca
Tue Sep 1 04:54:23 UTC 2015

> On 2015-August-31, at 02:28, Chan Kim <ckim at etri.re.kr> wrote:
> Hi, rtems users,
> Please someone help me fix my problem. I think this should be an easy question for those familiar with rtems
> I’m implementing a SD card driver and now can read, write files on SD card but it's very slow.

Without getting into the meat of your question, can you give me an idea of what is “very slow”?

I was doing some work with SD cards on n STM32F4 processor and the best I could get was about 475K/second. I tried everything, and after a week of mucking around with buffer sizes and optimizing the hell out of my code, I brought out my o-scope and figured out that the card (Class 10) was the bottleneck.

The speed ratings on SD cards means close to nothing. In this case it meant that you could READ at 10M/second, but writes were about 0.5M/second.

Switching from a Kingston (real, not counterfeit) to a store brand card more than doubled the throughput (4MB/sec write if memory serves me well).

Andrei from The Great White North

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