SD card on Teency 3.5
- Thread starter Lorenzo
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bit-clock rate.
OK this is not useful information.
maximal sustained write speed is depending on quality of uSD card and the amount of RAM you can dedicate for write buffer.
my rule of thumb is: max speed in bytes/s is max_buffer in bytes/0.1s.
This assumes max uSD delay is 100 ms. This max delay is not happen very often but it may happen multiple times / minute.
It also assume you use efficient file systems, e.g. exFat, and file pre-allocation etc.
On mean write speed there are various contribution in this forum, you will easily find by googling the forum.
PaulStoffregen
Well-known member
It varies quite a lot. Using the ordinary SD library is far from optimal, since it write 1 sector at a time. The audio library Recorder example is able to write 44.1kHz 16 bit stereo to every SD card I've tested, so there's at least one data point, 88 kbytes/sec works.
But at least a couple people have reported problems writing faster streams. I have not personally investigated.
You can achieve much better performance if you write in larger blocks. Bill's SdFat library does this, or can. It's quite a bit more complex than using the simple Arduino SD library. I personally haven't used it much, so I can't really help there.
Might also be worth mentioning, that audio Recorder example uses a "queue" feature of the audio library, where data is automatically saved in a queue during times you don't read fast enough. If you have a real time data source, that sort of buffering is pretty much always required for SD card writing. The cards usually respond quickly, but sometimes they can take many milliseconds. You do need a place to buffer your data while you sometimes wait for the SD card.
But at least a couple people have reported problems writing faster streams. I have not personally investigated.
You can achieve much better performance if you write in larger blocks. Bill's SdFat library does this, or can. It's quite a bit more complex than using the simple Arduino SD library. I personally haven't used it much, so I can't really help there.
Might also be worth mentioning, that audio Recorder example uses a "queue" feature of the audio library, where data is automatically saved in a queue during times you don't read fast enough. If you have a real time data source, that sort of buffering is pretty much always required for SD card writing. The cards usually respond quickly, but sometimes they can take many milliseconds. You do need a place to buffer your data while you sometimes wait for the SD card.
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