AM335x Boot from 1.8V eMMC

Thomas Kofoed-Hansen

Other Parts Discussed in Thread: AM3356

I want to boot a AM3356 from a 1.8V eMMC, but I'm struggling with a certain phrase in the technical reference manual (SPRUH73I). Else where the MMC1 port is described as supporting both 1.8V and 3.3V.

26.1.7.5.4 Initialization and Detection
The ROM Code initializes the memory device or card connected on MMC interface using the standard
High-Voltage range (3.3 V).

Does this mean that it's not possible to boot from a 1.8V eMMC, and if so can someone explain the reason why?

The pins are powered from VDDSHV1 which in my case is 1.8V. How should the register settings in register SD_CAPA (VS18, VS30, VS33), and register SD_HCTL (SDVS) be understood/used?

Thomas

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi Thomas,

You should be able to boot without problems. The ROM code has no means to change the VDDSHVx supply. By the way, update your TRM, latest revision is J.

0 Thomas Kofoed-Hansen over 10 years ago in reply to Biser Gatchev-XID

Intellectual 550 points

Thank you very much for the extremely quick answer. Sorry for toggling the "Answered" button, but I got a little confused there, but your answer was very precise and accurate.

0 Thomas Kofoed-Hansen over 10 years ago in reply to Thomas Kofoed-Hansen

Intellectual 550 points

I just have a follow up question.

What do the following register settings do/mean?

SD_HCTL - bits: SDVS

SD_CAPA - bits: VS18, VS30, VS33

Thomas

0 Biser Gatchev-XID over 10 years ago in reply to Thomas Kofoed-Hansen

TI__Guru**** 393215 points

I'm not a software expert but I wouldn't be surprised if these bitfields are not used in Linux.

0 JJD over 10 years ago in reply to Biser Gatchev-XID

TI__Guru 72070 points

Thomas, these bits are part of the SD host controller definition, but it is not used in the ROM code and they do not have any physical effect on the controller.

Regards,

James

0 Thomas Kofoed-Hansen over 10 years ago in reply to JJD

Intellectual 550 points

Thank you James for yet another clear answer.

Thomas

0 Rick Brower over 10 years ago in reply to Biser Gatchev-XID

Prodigy 130 points

I have a related question as well, regarding the use of UHS (ultra high speed) sd cards with the AM335x....

I noticed in the silicon errata document, #SPRZ360F it states in Section 3.1.5 "Only standard and high speed modes are supported. SDR12, SDR25, etc.... are not supported." Why is this the case? I understand that the SDR50 and the SDR104 versions require much faster clock speed, so it's obvious why they wouldn't be supported. On the other hand, the SDR12 and SDR25 seem analogous to the previous 'standard' and 'high speed' cards, with the exception of the 1.8V signal levels... So in principle they should still operate, correct?

You've already responded to the original post, indicated that a 1.8V card would boot, so can you shed any insight as to the reasoning behind the statement in the errata doc? Also, the SD Card association spec says that these UHS cards are powered off 3.3V, and initially communicate using 3.3V logic levels until commanded to switch down to 1.8V. Would this pose a problem on startup for MMC pins buffered off a 1.8V rail?

Thanks

0 Biser Gatchev-XID over 10 years ago in reply to Rick Brower

TI__Guru**** 393215 points

Hi Rick,

This thread discusses eMMC memories, not SD cards. The AM335X MMC interfaces have no voltage switching capability. They work either at 1.8V or 3.3V. This means that the SD card cage must be wired for 3.3V for the card to init correctly.

0 Rick Brower over 10 years ago in reply to Biser Gatchev-XID

Prodigy 130 points

Ah! Thanks for the clarification.

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AM335x Boot from 1.8V eMMC