Part Number:AM3352
Tool/software: Linux
Hi,
I have few questions related to the gpio configuration from u-boot till linux.
Use case:
- Make a pin (lets say H18 on ZCZ) as HIGH(3.3V)
Queries:
- What happens when we configure H18 in mux.c (u-boot) as OUTPUT_PULLUP ?
- What happens when we configure H18 in DTS as gpio-leds with default-on and ACTIVE_HIGH ?
- If there is a difference between the above mentioned two configurations, what is it and why is it ?
- Also, are there any other alternatives to gpio-leds, if yes, then kindly let me know what are they ?
- Is it duplication, if we have an entry of pinmuxing in mux.c and also in Device Tree ?
FYI:
- I am using a custom am3352 board and I am facing some issue with the voltage level of the pin which is connected to an external pull down resistor,
the problem is, when pinmux is configured, the voltage at the pin is 2.2V, when the same pin is configured as gpio-led, then voltage shifts to 3.3V,
Also, if I remove the pulldown resistor connected to the pin, then pinmux configuration itself is making this pin 3.3V - Pull Down resistance is 47K ohm
Behavior observed in linux:
| PullDown resistor Connected to H18 | Pinmux (mux.c in u-boot) | Device Tree | Voltage at H18 (when linux is up) |
| Yes | Configured as OUTPUT_PULLUP | not added as gpio-led | 2.2V |
| Yes | Configured as OUTPUT_PULLUP | added as gpio-led | 3.3V |
| No | Configured as OUTPUT_PULLUP | not added as gpio-led | 3.3V |
| No | Configured as OUTPUT_PULLUP | added as gpio-led | 3.3V |