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TMS320F28335: ADC Data logging

Muhammad Subhani
Intellectual 280 points
Part Number: TMS320F28335


Hi, 

My question is related to this post: https://e2e.ti.com/support/microcontrollers/c2000/f/171/t/539415

(I have tried clicking on the "Ask a Related Question" button, but it does not seem to work)

I want to sample two signals simultaneously at ~500 ksps and acquire about 128k samples of each signal. At the same time, I want to dump them into a safe location (but not the computer)

I was considering using an SD card as mentioned in spraoo7 guide. I want to know if I can write data into SD card at such high speeds. Further, is there an easier method to save the data (may be in some other storage medium/ space etc)

Also, is it possible to first dump all these samples in the F28335 onboard memory  and then transfer it to an SD card later?

Regards

  • 0
    TI__Guru* 81560 points

    Muhammad,

    I think you are on the right track.  There is not enough internal SRAM to hold 256k words of data.  That is the full amount of Flash on this chip, but the programming time is such that it wouldn't be able to keep up with your data rate.

    In the mode you have described you'll have 32-bits of data every 2us(technically 24 bits(2x 12 bits) but I'm simplifiying to 2 16 bit words for address alignement simplicity).  So, you would need data rate of ~ 16Mbps(including the write time of the SD card) to keep up with the converter.

    Based on some quick googling, I don't think you can acheive this across the SPI bus(I beleive max SD clock in this mode is 25MHz).

    You could use the XINTF and the 4-bit SD card transfer mode, and I think you can hit this datarate.  Once the interface is set up you could use the DMA on the C2000 to do the data transfers with no CPU overhead as well.

    https://www.sdcard.org/downloads/pls/pdf/index.php?p=Part1_Physical_Layer_Simplified_Specification_Ver6.00.jpg&f=Part1_Physical_Layer_Simplified_Specification_Ver6.00.pdf&e=EN_SS1 

    Let me know if this helps,

    Matthew

  • 0 in reply to MatthewPate
    Intellectual 280 points

    Dear Mathew,

    Thank you for the reply. It was most helpful.

    If I follow you correctly, it seems that I cannot use serial SRAMs either since they also operate using SPI bus and the data rate available with the F28335 will be a problem there as well.

    I have browsed briefly through the SD card physical layer document and I have a quick question. Does sequential writing into the SD card really mean that I will not have to add a header and crc etc each time I write a byte? 

    Regards,