iMX7D boot USDHC3 1V8

[thomaskofoedhan]

It's possible to set the voltage for ports USDHC1-2 via pull-up/down resistors on the LCD BOOT_CFG pins, but the USDHC3 setting has to be done by sw.

I would like to boot from the USDHC3 interface connected to an eMMC with 1V8 IO voltage, because it's the eMMC port that supports the fastest interface (HS400 using strobe). But the default register (0x4A0[1]) setting is 3V3, so my question is is there any way to accomplish what I want?

Another question is why are these voltage settings necessary, does the CPU actually change the pin voltage according to these settings regardless of what the GPIO power bank is connected to?

[igorpadykov]

Hi Thomas

there is USDHC3  fuse setting described in Table 6-17. Boot Fusemap i.MX7D

Reference Manual  address 0x4A0[7:0]
http://cache.nxp.com/files/32bit/doc/ref_manual/IMX7DRM.pdf
voltage is defined by bit VSELECT register uSDHCx_VEND_SPEC and software uses it.

Best regards
igor
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[thomaskofoedhan]

Hi Igor,

I think you misunderstood me. I know the registers and the fuse settings, but I want to know -

a) Is it possible to boot from an 1V8 eMMC on the USDHC3 port, on which it is not possible to set the voltage with external resistors?

b) Does the CPU actually change the pin voltages according to the fuse settings disregarding the power bank supply for these pins?

Thomas

[igorpadykov]

Hi Thomas

>a) Is it possible to boot from an 1V8 eMMC on the USDHC3 port, on which it is not possible to set the voltage with external resistors?

could you clarify what do you mean

>b) Does the CPU actually change the pin voltages according to the fuse settings disregarding the power bank supply for these pins?

sorry, I did not understand that too. Processor sets bit VSELECT register uSDHCx_VEND_SPEC

according to fuse setting. How processor could know power bank supply for pins?

Best regards
igor

[thomaskofoedhan]

Hi Igor,

boiled down, what I'm trying to understand is the function of the fuse bit voltage setting.

Each and all pins on the processor are connected to an internal power group (NVCC_x etc.), including the eMMC SDIO pins. So my question is what does it mean when I chose 1V8 or 3V3 by setting the fuse bits? Example: If the pin is in a power group supplied by 1V8, what happens if I set the fuse bit to 3V3 or vica versa?

Thomas

[igorpadykov]

Hi Thomas

setting the 1V8 or 3V3 fuse bits lets processor to know what
power would be used for pins and boot ROM sets bit VSELECT accordingly.> If the pin is in a power group supplied by 1V8, what happens if I set the fuse bit to 3V3 or vica versa?nothing. If you are speaking about USDHC, its voltages and usage is defined by SD specs (the same for eMMC).
For example SD init voltage should always be 3.3v, then for UHS-I (depending of that fuse setting)
boot ROM may configure IO pad 1.8 voltage level. Switching is performed by external power switch controlled by
SD_VSELECT pin.

Best regards
igor