AM335X SD card - speed class and size supported

Rodrigo Aznar Mendes

Prodigy 215 points

Hi All,

We are going to use the MMC0 to boot the system using a SD card.

The AM335X manual mention in chapter 18:

"- SD Host Controller Standard Specification sets as defined in the SD card specification Part A2
v2.00

- up to 192Mbit/sec (24MByte/sec) in High-Speed SD mode 4-bit data transfer

- up to 24Mbit/sec (3MByte/sec) in Default SD mode 1-bit data transfer"

The SD card specification explains the speed classes and respective read speed (MB/s).

Our design will use a 4-bit SD card.

Does anyone know:

- Which is the highest SD speed class supported ?

- What is the size limit supported for a SD card? (consider AM335X and linux kernel limits)

Thanks

Rodrigo

over 12 years ago

0 Rodrigo Aznar Mendes over 12 years ago

Prodigy 215 points

Hello

Does anyone from TI have some directions on the questions listed?

Thanks

Rodrigo

0 -DK- over 12 years ago

TI__Mastermind 27890 points

Hi Rodrigo,

AM335x supports the maximum formatted card size as defined by the SD 2.0 (SDHC) specification @ 32GB. In fact, we now have SDXC 64GB cards working well after reformatting from the default exFAT to ext3 filesystem. I haven't seen any throughput numbers yet; perhaps someone else will chime in with them.

-DK

0 Renjith Thomas over 12 years ago in reply to Rodrigo Aznar Mendes

Guru 31670 points

Rodrigo,

I don't have enough data on the questions that you posted. But, are you looking forward to optimize the current speed of SD? If so, what is the current throughput that you are getting?

0 Rodrigo Aznar Mendes over 12 years ago in reply to Renjith Thomas

Prodigy 215 points

Hi Thomas, We have not finished the hardware design yet. My point was to have an idea on how critical are the SD lines in terms of PCB layout. Would you have a equivalent clock speed to have in mind during PCB layout for the SD card? thanks a lot Rodrigo

0 Renjith Thomas over 12 years ago in reply to Rodrigo Aznar Mendes

Guru 31670 points

Hi Rodrigo,

I'm not a hardware expert. But the best clock speed at which you are going to drive the SD_CLK will be to the tune of 52MHz (Best case). I may not be 100% correct here.

0 cahide sen over 8 years ago in reply to -DK-

Prodigy 130 points

Is reformatting SDXC card to ext3 filesystem a "must" when working with am335x ?

If this filesystem reformatting a must, are there any additional workarounds the developer is expected to perform?

thank you,

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AM335X SD card - speed class and size supported