Verdin AM62 - How to set voltage of MMC1-Pins

Technical Support
,
1

Hello Community,
we are using the Toradex Verdin AM62 SoM on a Carrierboard and would like to make use of UART3. We run Torizon OS but also work with yocto builds. We need many UARTs, and need to use UART3 so we have to use the SD card pins in alternate function mode:
for example the UART3_TX pin was previously used as MMC1_CMD pin:
{8424EFE7-6A67-46F6-BCB9-B8943535C7B0}

and the RX pin was used as MMC1_CLK pin

{B436CFDC-A4A6-40EC-BB80-CAB0D63F35C9}
{B436CFDC-A4A6-40EC-BB80-CAB0D63F35C9}1537×125 12.4 KB

I know that the SD cards need to be driven with 3.3V (but might be switched to 1.8V), and so the UART3 pins actually work with 3.3V. We want to have 1.8V instead.

I dont know the on-SoM structure of the power-supplies and wanted to ask, if and how it is possible to lower the voltage on the UARTs from 3.3 to 1.8V?

I am thinking of a device tree overlay to overwrite:

	reg_sdhc1_vqmmc: regulator-sdhci1-vqmmc {
		compatible = "regulator-gpio";
		pinctrl-names = "default";
		pinctrl-0 = <&pinctrl_vsel_sd>;
		/* PMIC_VSEL_SD */
		gpios = <&main_gpio0 21 GPIO_ACTIVE_HIGH>;
		regulator-name = "LDO1-VSEL-SD (PMIC)";
		regulator-min-microvolt = <1800000>;
		regulator-max-microvolt = <3300000>;
		states = <1800000 0x0>,
			 <3300000 0x1>;
		vin-supply = <&reg_sd_3v3_1v8>;
	};

but am not sure how to do that and if that is safe then without disabling some other 3.3V peripherals. We do not want to use MMC1 at all.

We also disabled it in U-boot as it tried booting from the MMC1 as well.

Kind regards,
Dominik

2

Hi, I’m the Toradex AI Assistant.

I might make mistakes or occasionally get you wrong. Our support team will step in if needed.

I’d be glad to help with configuring UART3 on your Verdin AM62! To provide you with the most accurate guidance for your specific setup, could you let me know which version of Torizon OS you are running? You can get this information using the tdx-info command on your device, which will provide detailed system information - more details at tdx-info.

Understanding Your UART3 Configuration Challenge

Your approach to repurpose the MMC1 pins for UART3 functionality is technically sound, and the voltage switching concept you’re considering is on the right track. The Verdin AM62 does indeed use a voltage-switchable power supply for the SD card interface that can operate at either 1.8V or 3.3V(1).

Device Tree Overlay Approach

Based on the documentation for writing device tree overlays(1), you’ll need to create a comprehensive overlay that:

  1. Configures the pin multiplexing to switch MMC1_CMD and MMC1_CLK pins to UART3_TX and UART3_RX functions
  2. Disables the MMC1 interface to prevent conflicts
  3. Manages the voltage regulator for the desired 1.8V operation
  4. Enables UART3 with proper pin control settings

The voltage regulator you identified (reg_sdhc1_vqmmc) is indeed the correct one for controlling the voltage on those pins(1).

Next Steps

Once you provide your Torizon OS version, I can give you specific guidance on:

  • The exact device tree overlay structure needed for your configuration
  • How to safely modify the voltage regulator settings
  • Proper pin control configuration for UART3 on those specific pins
  • How to build and deploy the overlay using TorizonCore Builder or Yocto methods

The configuration you’re planning should be safe since you’re not using MMC1, but the exact implementation details will depend on your OS version.

Best regards, Toradex AI Assistant.

Did you like my answer? :+1: :-1:

If I answered your question, please tick the “Solution” checkbox.

For follow-up questions to me, please use @ToradexAI in your post.

3

Yes it’s safe since only SD card domain is affected. The voltage is controlled by gpio0 21 (High - 3.3V, Low 1.8V). You can set it low using GPIO hog property.