SD read speed in raw 512 byte mode on Teensy 3.6 and 4.0

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kdharbert

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I have a real-time audio application where I need to overlay audio samples in an output audio stream. The Teensy memory can't hold the samples, so they well be held on an SD card. I need high speed access to the SD so I'm going to use raw 512 byte mode. I need to make calculations for accessing arbitrary 512 byte blocks. It seems like I could make calculations for read speed, but I'm sure there's twelve catches. Can anyone offer data on block SD reads for Teensy 3.6 and 4.0?
 
If you are asking for code on block SD read then I recommend the library SimpleSDAudio.
Yesterday I opened a post "speed up SD card transfer" asking how to speed up SD data transfer with that library. The library initially is written for Arduino controllers with 16 MHz. I modified it for Teensy 3.2. But my problem with this library is that I don't know how to use the much higher clock rates of Teensy controllers to speed up data transfer. If you can solve that problem you have a solution for your app and it helps me too :)
 
A library probably wont work for me. The audio work I need to do is unorthodox and very specific. All I really need is a function I pass an address to and I get the 512 byte block back when an interrupt is thrown on completion. I need to calculate how many cycles it would take to run.
 
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