SD CARD at SDR104: How to?


we just started to develop custom HW based on Jetson Nano. Where can we find info about how to make SD CARD work at SDR104 speed? I mean:

  1. Circuit suggested for voltage switching between 3.3V and 1.8V.
  2. Pins for control the voltage switch and DTS config.


  1. Do modules for EVK, with integrated micro SD, work at 1.8V or 3.3V?.
  2. Are production SOM identical to EVK SOM but with micro SD instead of eMMC. We just orderer some production samples to test but we are not sure about the real differences.

Thank you in advance!

Please refer to the product design guide of nano in DLC for SD card design. No hw circuit is needed to switch voltage. It is eMMC on production module.

Do you mean you want to fix it in SDR104? or just doing the normal the voltage switch but highest one supports to SDR104?

Did you already apply those patches to your DT for enabling SDMMC3?

Thank you Both,

Trumany: we want to use also SD CARD and as fast as possible.

WayneWWW: I can see that it is necessary to apply a patch to make SD card and eMMC work at the same time but it wasn’t what i meant. AFAIK you canno’t initialize an SD Card in UHS mode but you need to init in HS, then change the voltage from 3.3V to 1.8V, change processor registers config, wait a delay and then SD card moves to UHS.In that case it would be needed more than a simple load switch. Am I wrong?. At least it happened to us with other processors but in these cases the sd card supply was driven by an internal PMIC voltage rail…


The card should have a 1.8V regulator inside. It will switch card voltage level from 3.3v to 1.8v as set. The IO voltage of nano port can be switched to 1.8v too.

From software configuration, you can refer to the kernel source file document.


There are some properties that might limit the mode.

uhs-mask: Specify modes that are masked for the device
 	Mask HS200 mode: 0x20
 	Mask HS400 mode: 0x40
 	Mask SDR104 mode: 0x10
 	Mask SDR50 mode: 0x4
 	Mask DDR50 mode: 0x8

Thank you both!,

it seems that I was confused and is not an issue about powering the SD Card but about the voltage levels on data lines and as the documentation of the SOM specifies that these lines support both 1.8V and 3.3V now I can see that there are no extra HW requeriments but only SW configuration needed.

Best regards,