task not relinquishing scheduler busy waiting..

[Chan Kim]

> Without getting into the meat of your question, can you give me an idea of
> what is “very slow”?
I feel ashamed to tell but to write 0.5MB file, I have to wait about 20 seconds(0.5MB/20sec = 25kB/sec) and this is absurd.
I still have some delay element that I put in that I have to remove, but currently looking a a synch problem. I hope fixing this problem will let me remove delays(or waits) that I put in not knowing exactly the cause.. I'm learning rtems alot these days :)
regards,
Chan



보낸 사람 : "Mr. Andrei Chichak" <groups at chichak.ca>
보낸 날짜 : 2015-09-01 13:54:30 ( +09:00 )
받는 사람 : RTEMS List <rtems-users at rtems.org>
참조 : 
제목 : Re: task not relinquishing scheduler busy waiting..


> On 2015-August-31, at 02:28, Chan Kim 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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