SPI1 works, but CS0 not

[astirfreak]

Hi,
I have PI2+, with a working waveshare display clone. To control a second SPI device (potentiometer) I like to use SPI1.
In the config.txt I added

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dtoverlay=spi1-1cs

To control the SPI, I use Python with spidev.
My testcode is:

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import spidev
spi = spidev.SpiDev()
spi.open(1,0)
spi.max_speed_hz=50000
spi.cshigh=False 			# |
spi.cshigh=True 			# -> No effect if one of this lines is used
spi.xfer([0xAA])
spi.close()

I can see clock on DCLK (Pin 40) and data an MOSI (Pin 38).
On pin 36 (SPI1_CS0) I cannot see anything. It has a constant low level.

To check, if there is a hardware problem I tried:

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import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
GPIO.setup(16, GPIO.OUT)	
GPIO.output(16,1)

With that code I can see, the pin 36 (GPIO16) is working.

Whats wrong here?

Michael

[astirfreak]

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dtoverlay=spi-gpio35-39

doesn't work for me.
The display then doesn't work anymore and no spi is visible in /dev

[astirfreak]

Further findings:
https://pinout.xyz/pinout/spi#
It uses the CS0 on Pin12 (GPIO18). I can see it on this pin with my oscilloscope.

Pin 36 isn't CS0 for SP1 as mentioned in


Pin 12 is blocked by the display.
To use Pin 36 instead I have to create an own overlay. Now I have to google how to do that.

Michael

[astirfreak]

Does anyone know, where to find the original code of spi1-1cs.dtbo?
I only find the precompiled versions but I want to modify it and compile it by myself.

Michael

[ericcooper]

It's in arch/arm/boot/dts/overlays/ on https://github.com/raspberrypi/linux, rpi-4.9.y branch

[astirfreak]

Thank you, now I got it working:

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/dts-v1/;
/plugin/;

/ {
        compatible = "brcm,bcm2835", "brcm,bcm2708", "brcm,bcm2709";

        fragment@0 {
                target = <&gpio>;
                __overlay__ {
                        spi1_pins: spi1_pins {
                                brcm,pins = <19 20 21>;
                                brcm,function = <3>; /* alt4 */
                        };

                        spi1_cs_pins: spi1_cs_pins {
                                brcm,pins = <16>;
                                brcm,function = <1>; /* output */
                        };
                };
        };

        fragment@1 {
                target = <&spi1>;
                frag1: __overlay__ {
                        /* needed to avoid dtc warning */
                        #address-cells = <1>;
                        #size-cells = <0>;
                        pinctrl-names = "default";
                        pinctrl-0 = <&spi1_pins &spi1_cs_pins>;
                        cs-gpios = <&gpio 16 1>;
                        status = "okay";

                        spidev1_0: spidev@0 {
                                compatible = "spidev";
                                reg = <0>;      /* CE0 */
                                #address-cells = <1>;
                                #size-cells = <0>;
                                spi-max-frequency = <125000000>;
                                status = "okay";
                        };
                };
        };

        fragment@2 {
                target = <&aux>;
                __overlay__ {
                        status = "okay";
                };
        };

        __overrides__ {
                cs0_pin  = <&spi1_cs_pins>,"brcm,pins:0",
                           <&frag1>,"cs-gpios:4";
                cs0_spidev = <&spidev1_0>,"status";
        };

I only replaced the two entrys of the CS-Pin from 18 to 16.

If the the device tree compiler is not installed it has to be installed:

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sudo apt-get install device-tree-compiler

After that I compiled my dts:

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 dtc -@ -I dts -O dtb -o spi1-1cs36.dtbo spi1-1cs36.dts 
                    
spi1-1cs36.dtbo: Warning (unit_address_vs_reg): Node /fragment@0 has a unit name, but no reg property
spi1-1cs36.dtbo: Warning (unit_address_vs_reg): Node /fragment@1 has a unit name, but no reg property
spi1-1cs36.dtbo: Warning (unit_address_vs_reg): Node /fragment@2 has a unit name, but no reg property

I got that warnings but I ignored it.

Now the dtbo has to be copied:

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sudo cp spi1-1cs36.dtbo /boot/overlays

The last step is to add it to the boot.cfg:

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sudo nano /boot/config.txt

And here I added a new entry as last line:

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dtoverlay=spi1-1cs36

[vybhav]

Hi
I made the above changes (dtoverlay=spi1=1cs) in the config.txt.
In the program when i wrote spi.open(1,0) i am getting an error "[Errorno2] no such file or directory "
can anyone help me out in using spi1(python code)

Thank you