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SDIO Hardware Flow Control

Question asked by Chuck on Dec 17, 2013
Latest reply on Dec 27, 2013 by dmitriev.ivan.001
Greetings all, I've been playing around with SDIO on an STM32F4 -Discovery card with the Embest Baseboard on it. My goal is to get it to work in polling mode, flow control mode, interrupt mode, and dma mode. This is for a book I am writing. 

Generally the various bits of documentation can be puzzled out. But the flow control stuff is a bit of a mystery. 

So I started with a polled version of my code, this does all the various commands and spin loops on the status register. And it works fine. So I wanted to demonstrate it doing "flow control". If I send a read command, and then delay pulling stuff out the FIFO, it fills up as expected but it doesn't stop filling.  It just fills up, the clock keeps running, and CRC error comes on. 

So I begin to wonder if I need things set in the DCTRL to make this work. I tried RWSTART, RWSTOP, and RWMOD (my setup is running a 4 bit bus so it needs to use SDIO CLK to stop things). None of them seemed to have any effect. (I still get essentially a RXFIFO overrun and CRC errors).  So are there any additional docs on this feature of the SDIO peripheral?