SD CARD communication and TX UNDERRUN error

[aut]

Hi all,

with reference to the LPC1788 microcontroller, I have some problems with the SD CARD routines. I'm using  the lpc177x_8x_mci.c routines 2.0 version but I have frequently TX UNDERRUN errors. Is this a my mistake or the NXP routines are not reliables? 

Many thanks   

[FelipeGarcia]

Hi Nico,

I recommend you to use the newest LPCOpen library. Inside the library you can check the latest SDMMC card example and drivers. Please download LPCOpen library from the following link.

LPCOpen Software for LPC17XX | NXP

Or If you have MCUXpresso already installed in your PC you can check the examples in the following path.

C:\nxp\MCUXpressoIDE_11.0.1_2563\ide\Examples\LPCOpen\lpcopen_2_10_lpcxpresso_ea_devkit_1788.zip

I hope this helps.

Best regards,

Felipe

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[aut]

Sorry, in my previous post I was wrong to write. The error isn't TX OVERRUN but TX UNDERRUN  

[FelipeGarcia]

Hello Nico,

You are correct, TX underrun means that the FIFO is transmitting data at a higher speed than the speeds the data comes to the FIFO.

Unfortunately, the only way to avoid this issue is to make sure that your FIFO has always values so your FIFO will not be empty when a new transmission request arrive, triggering FIFO underrun.

Hope it helps!

Have a great day,
Felipe

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[aut]

Hi Felipe.

Doing various tests, the problem occurs also in reception (TX OVERRUN) which is worse than the TX UNDERRUN because you can't recover it in any way (more data comes than that the uP can manage). Both problems (TX OVERRUN and TX UNDERRUN) don't occur up to a clock frequency of 3MHz. I unfortunately would like to go much higher, at least 15MHz. The value 20MHz would be ideal. I have to try using the DMA. Do you think it will work well?

Thanks

[FelipeGarcia]

Hi Nico,

DMA will definitely allows you to transfer at a higher frequency. However, you will need to test first if it fits the frequency you need.

Best regards,

Felipe

[aut]

Hi Felipe.
Many thanks for your advice.

For the moment I by-passed the problem by writing or reading again the block (512 byte) where the problem has occurred. In this way, the data exchange goes on and ends successfully. I looked the last library version you recommended me but I didn't try it. Aniway, it seems to me that even in these new routines the data exchange stops if the TX OVERRUN error occurs. I noticed that using 400KHz clock the problem never occurs. Increasing the clock the problem starts and it becomes more and more frequent when the clock is increased up to 15MHz.

I don't use the DMA, I use the FIFO interrupts. If I well understood, the problem occurs because the FIFO emptying is much faster than the FIFO loading. Maybe it is normal with the FIFO interrupts. My question now is: is there any why to avoid the TX OVERRUN error?

Thanks