I am using an STM32F4 microcontroller with a microSD card. I collect analog data through DMA.
I use a double buffer, taking 1280 (10 * 128 - 10 FFT) samples at a time. When one buffer is full, I set the flag, and then look at 128 samples at a time and run the FFT calculation on it. It all works well.
The data is taken with the frequency I want, and the FFT calculation will be what I expected. If I just let the program run for one second, I see that it launches the FFT approximately 343 times (44000/128).
But the problem is that I would like to save 64 values from this FFT to the SD card.
- I am using the HCC file system library.
- Each FFT calculation cycle I copy 64 values to an array.
- After every 10 calculations, I write the contents of this array to a file and start over.
- The array stores 640 float_32 values (10 * 64).
This works great for a one second test run. I get 22,000 values stored on an SD card.
But as I increase the time, I begin to lose counts, as the SD card takes longer to record. I need an SD card to store more than 87 bps (4 bytes * 64 * 343 = 87808). I tried to increase the sample size of the DMA buffer, and then the number of times it writes, but did not find this to help.
I use an 8G microSD card, class 4. I formatted the SD card to the default FAT32 distribution block size by default of 2048.
? , . ? , - ?
, clifford , , SD- 16- 48 ksamples/s?.