For the design of a new colibri carrier boards, we were looking into the possibility of using SDHC1 on a fixed 1.8V level for interfacing with an SDIO module.
The toradex colibri datasheet clearly specifies that SD1_CLK, SD1_CMD and the first 4 datalines can be powered at 1.8V.
From what I see in the linux kernel device tree, the reg_sd1_vmmc regulator is used for this, which is controlled by GPIO5_9 (MX6ULL_PAD_SNVS_TAMPER9__GPIO5_IO09).
As far I can see, driving this pin high should cause some regulator on the IMX SOM to drop the NVCC_SD to 1.8V, and hence lower the bank voltage.
To confirm this, I quickly did a test, where I disable the regulator control in the device tree and put both MX6ULL_PAD_SNVS_TAMPER9 and MX6UL_PAD_SD1_CLK in GPIO mode, and drive the signals.
The result is however that with MX6ULL_PAD_SNVS_TAMPER9 driven high, the output of SD1_CLK goes down to 3V, but NOT to 1.8V.
Am I missing something here?
What is the internal connection of NVCC_SD on the module? Is my understanding correct of trying to manually force the 1.8V? If not, how can this be achieved then?
Thanks for your reply,