i.MX ProcessorsのトピックRe: gpio

gpio

wgoodrich — Wed, 29 Aug 2018 19:27:08 GMT

For the i.mx8M:

It is possible to have a 95K pull-down on an output pad, since most pads of the i.mx8 are configured that way coming out of reset.

But in the IOMUXC_SW_PAD_CTL_PAD_xxx registers, the only option is to enable a pull-up (which I assume to be 27K).

Is that really true? Once out of reset, my only option is to enable a pull-up?

Re: gpio

igorpadykov — Thu, 30 Aug 2018 23:30:04 GMT

Hi Whit

out of reset pad state can not be changed and described in

Table 83. i.MX 8M Dual / 8M QuadLite / 8M Quad 17 x 17 mm functional contact assignments

i.MX8MDQ Datasheet
https://www.nxp.com/docs/en/data-sheet/IMX8MDQLQCEC.pdf

Best regards
igor
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Re: gpio

wgoodrich — Fri, 31 Aug 2018 12:48:51 GMT

Hi Igor,

Thanks for your reply! I need to re-phrase my question:

When the OS is running and is configuring the Pad control registers, how do

I enable the 90K pull-down when I am setting the other input pad

parameters. If, for example, I set up a GPIO with a Schmitt trigger input

and LVTTL in the pad control register, is the 90K pull-down still there? If

the 90K pull-down is there, how do I disable it? if it’s not there, how do

I enable it (these are the different cases I have across the design).

Thanks!

-Whit Goodrich

Izotope inc.

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To: Whit Goodrich <wgoodrich@izotope.com>

Subject: Re: - Re: gpio

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Re: gpio

reply from igorpadykov

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Re: gpio

igorpadykov — Fri, 31 Aug 2018 23:29:49 GMT

Hi Whit

processor pad settings (and pull resistor) are set in dts file, as in example

    imx8mq-evk {
       pinctrl_hog: hoggrp {
           fsl,pins = <
               MX8MQ_IOMUXC_NAND_READY_B_GPIO3_IO16       0x19
               MX8MQ_IOMUXC_NAND_WE_B_GPIO3_IO17       0x19

fsl-imx8mq-evk.dts\freescale\dts\boot\arm64\arch - linux-imx - i.MX Linux kernel

Best regards
igor

Re: gpio

wgoodrich — Tue, 04 Sep 2018 13:57:16 GMT

Hi Igor,

OK, I think you have answered my question in a round about way:

There is no way in software to control the state of the PULL_DOWN resistor that is present in a GPIO circuit of an IMX8M. This differs from the operation of the imx6. In the imx8 I can program the state of the GPIO PULL_UP resistor, but not the the PULL_DOWN resistor.

Is that correct?

Thanks,

-Whit