Hello,
I am trying to understand if I am able to use the SPI pins as GPIO when SPI is not being used. This post says that we could be able to use I2C and SPI pins besides normal GPIO pins, but if there is a way, I can't seem to find it.
Thank you,
Aleix.
Hi Karl,
First of all thank you very much for your extended reply. 
Now that I know that theoretically it is possible, I give you additional information:
-For consumption purposes, we have disabled the power supply for the nRF52840 and therefore all SPARE pins are unavailable.
-We are already using all of the NMOS pins to control the power supply towards 3 different external sensors.
-To communicate with the sensors we are using I2C so using them is not an option either.
-We are interested in using the SPI pins because we created a little PCB that has a connection to TP34 which if I remember correctly is the SPI-SCK by default, P0.03.
-If this was not possible, we would have a plan B: trying to get rid of the necessity of using this pin. Even a plan C: getting a cable towards pin P0.10 which I think is an additional free (or partially free, with a little hardware change) GPIO.
But I have had trouble trying to configure this SCK-SPI (P0.03) to work as a GPIO. Could you give me some advice on how to do it? I have tried the following:
gpio_dev = device_get_binding("GPIO_0");
gpio_pin_configure(gpio_dev, #pinSCK-SPI(P0.03)#, GPIO_OUTPUT_HIGH);
But I don't see the pin rising.
I have also tried to change the .overlay file redirecting the sck pin to another one, making it "free". But I guess that since I don't have any configuration related to SPI in the proj.conf file, the spi configuration does not update because it is disabled. Just in case, I add my configuration file:
#CONFIG_UART_0_NRF_UARTE=y # General config CONFIG_ASSERT=y # Network CONFIG_NETWORKING=y CONFIG_NET_NATIVE=n CONFIG_NET_SOCKETS=y CONFIG_NET_SOCKETS_OFFLOAD=y # BSD library CONFIG_BSD_LIBRARY=y # AT host library CONFIG_AT_HOST_LIBRARY=y CONFIG_UART_INTERRUPT_DRIVEN=y # Stacks and heaps CONFIG_MAIN_STACK_SIZE=4096 CONFIG_HEAP_MEM_POOL_SIZE=4096 # i2c CONFIG_LOG=y CONFIG_I2C_LOG_LEVEL_DBG=y CONFIG_LOG_BACKEND_UART=n CONFIG_I2C=y CONFIG_I2C_NRFX=y CONFIG_I2C_2=y #CONFIG_I2C_2_NRF_TWIM=y # Enabling printf and floats CONFIG_NEWLIB_LIBC=y CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y # Enabling JSON CONFIG_CJSON_LIB=y #gpio CONFIG_GPIO=y #debug RTT CONFIG_CONSOLE=y CONFIG_RTT_CONSOLE=y CONFIG_USE_SEGGER_RTT=y CONFIG_UART_CONSOLE=n CONFIG_SERIAL=y CONFIG_LOG_IMMEDIATE=y #wdt CONFIG_WATCHDOG=y
Thanks for your time,
Aleix.
Hello again Aleix,
Krawlow said:First of all thank you very much for your extended reply.
No problem at all, I am happy to help!
Krawlow said:-For consumption purposes, we have disabled the power supply for the nRF52840 and therefore all SPARE pins are unavailable.
-We are already using all of the NMOS pins to control the power supply towards 3 different external sensors.
-To communicate with the sensors we are using I2C so using them is not an option either.
Thank you for the additional information, this is very helpful!
You say that you are using all the NMOS pins, but only mention 3 external sensors - do you mean that you are using all four NMOS? I am just asking to avoid any misunderstandings.
Krawlow said:-We are interested in using the SPI pins because we created a little PCB that has a connection to TP34 which if I remember correctly is the SPI-SCK by default, P0.03.
You remember correctly, TP34 accesses SPI-SCK at P0.03.
My suggestion would be to instead use the UART1 rts and cts ( hardware flow control pins ), since they are unused anyways, so that you do not loose the SPI.
This can be done like the following:
&uart1 {
/delete-property/ rts-pin;
/delete-property/ cts-pin;
};Krawlow said:But I don't see the pin rising.
I would think that you should be able to control P0.03 using the modifications you have described.
How did you disable the SPI, something like this: ?
&spi3 {
status = "disabled";
};Krawlow said:plan B: trying to get rid of the necessity of using this pin.
If you do not mind telling me, what will the pin be used for?
Krawlow said:plan C: getting a cable towards pin P0.10 which I think is an additional free (or partially free, with a little hardware change) GPIO.
Yes, if you are neither using the nRF52840 nor the INT2 of the ADXL's then you may use this pin as GPIO also, this is correct.
Best regards,
Karl
Hello Karl,
I will copy you in the way of answering if you don't mind
You say that you are using all the NMOS pins, but only mention 3 external sensors - do you mean that you are using all four NMOS? I am just asking to avoid any misunderstandings.
Yes, that was a mistake of mine. We are using all of the NMOS, 3 of them as a power supply switch for 3 different sensors and for the fourth we are using its associated GPIO for an external magnetic switch.
My suggestion would be to instead use the UART1 rts and cts ( hardware flow control pins ), since they are unused anyways, so that you do not loose the SPI.
We could also consider this, but was not able to find any suitable location on the Thingy where we could connect to these pins, I think they don't appear on the User Guide.
I would think that you should be able to control P0.03 using the modifications you have described.
How did you disable the SPI, something like this: ?
When I put this lines in "thingy91_nrf9160ns.overlay" I get the following error trying to load the project:
If you do not mind telling me, what will the pin be used for?
No problem: we will use the additional GPIO to trigger the enable pin of a voltage converter up to 5 volts. We are trying to control power consumption here. To avoid using an additional GPIO we would connect the enable pin directly to the NMOS pins which would have some disadvantages in terms of power consumption:
-We would have to mantain this pin up, and subsequently the sensor of that pin throughout all of the read of the remaining sensors.
-Adding up-time to the first sensor for the necessary waiting of the power converter prior to having an stable voltage.
Thanks for the help!
Aleix.