i.MX6ULL EVK - Toggle BT_nPWD (BT_PWD_L)

[daweichen]

Hi NXP,

Per the i.MX6ULL EVK schematic, BT_nPWD is routed to a serial-in-and-parallel-out register.

I am using the default imx6ull-14x14-evk.dts for NXP's i.MX6ULL EVK board.

Is there a way for me to toggle the state of this signal (BT_nPwD) via a Linux's user-space command during run-time?

I guess the alternative is to re-purpose (rewire) the BT_DISABLE, which I don't need for my Bluetooth module.

Thanks!

Dawei

[igorpadykov]

Hi Dawei

BT_nPwD is controlled by 74LV595PW  U2101  serial-out shift register

and I am afraid it not can be used directly through linux user-space commands.

Best regards
igor
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[daweichen]

Hi Igor,

Thank you for the clarification. 

Is there a way to toggle the state of the signal?  (understand it can't be changed via a user-space command.)

dawei

[daweichen]

It looks like it can be changed through the DTS file.

                gpio_spi: gpio_spi@0 {
                        compatible = "fairchild,74hc595";
                        gpio-controller;
                        #gpio-cells = <2>;
                        reg = <0>;
                        registers-number = <1>;
                        registers-default = /bits/ 8 <0x57>;
                        spi-max-frequency = <100000>;

[igorpadykov]

Hi Dawei

it is necessary to send to 74LV595 data sequence

for changing that signal. One can look at 74LV595 datasheet

for more details. One can find on web helpful tutorials for gpio expanders, like:

Interfacing an I2C GPIO expander (MCP23017) to the Raspberry Pi using C++ (i2cdev) · Hertaville.com 

Best regards
igor

[daweichen]

Hi Igor,

I would like to do something quick. 

Would I be able to export BT_DISABLE (SNVS_TAMPER1) to sysfs and toggle the state by using the echo command?

If so, would you be able to tell my the correspond GPIO number?

Example: 

echo 106 > /sys/class/gpio/export

echo out > /sys/class/gpio/gpio106/direction
echo 0 > /sys/class/gpio/gpio106/value

Thanks,

dawei

[igorpadykov · Accepted solution]

Hi Dawei

in general it is possible as for example below

SPI Example: olinuxino GPIO expander 

Best regards
igor

[daweichen]

Thank you very much, Igor.

I was able to export the gpio508 to sysfs and toggle the discrete output (BT_nPWD) state. 

By doing an "ls -la" command in the /sys/class/gpio directory command, I was able to see the spi-gpio expander starts with gpio number 504.