In iMx6Q uSDHC module, there are three options to read from / write to SD Card:
1-> Internal DMA, Over AHB Bus
2-> External DMA, Over IP Bus
3-> PIO, reading a register
What are the advantages/disadvantages or considerations about these methods? In my opinion:
a-) Reading a file via PIO is the slowest one and also makes CPU busy. This is not an efficient way. Then in which circumstances should we think to use this way?
b-) Internal DMA is special to uSDHC. It provides us not to occupy external DMA, so it seems an efficient way to use resources of the chip. However I am not sure about comparison of internal/external DMA speeds.
What are your experiences/thoughts?