Enabling ADC on a Beaglebone Black running FreeBSD 12.0-CURRENT (BEAGLEBONE)

[Dr. Rolf Jansen]

Am 12.03.2017 um 10:57 schrieb Dr. Rolf Jansen <rj at obsigna.com>:

> I experience problems to enable the ADC line of my BBB.
> 
> Apparently, in FreeBSD 10, the ADC lines would have been enabled by a sysctl call:
> 
>   sysctl dev.ti_adc.0.ain.0.enable=1
> 
> 
> On FreeBSD 12, this gives:
> 
>   sysctl: unknown oid 'dev.ti_adc.0.ain.0.enable'
> 
> 
> I thought, perhaps the driver has not been loaded into the kernel, but:
> 
>   kldload ti_adc
>   ....
>   kldload: can't load ti_adc: module already loaded or in kernel
> 
> 
> Question:
> 
> What do I need to get the ADC working with FreeBSD 12?

I am answering my own question.

The ADC is disabled in the respective device tree file am335x-boneblack.dtb. In order to enable the it, I did:

1. decompile the device tree blob (.dtb) into a device tree source file (.dts):

   cd /boot/dtb
   dtc -I dtb -O dts am335x-boneblack.dtb > am335x-boneblack.dts


2. edit the .dts file, and change the entry for tscadc to the following:

		tscadc at 44e0d000 {
			compatible = "ti,am3359-tscadc";
			reg = <0x44e0d000 0x1000>;
			interrupt-parent = <0x1>;
			interrupts = <0x10>;
			ti,hwmods = "adc_tsc";
			status = "okay";
			dmas = <0x29 0x35 0x0 0x29 0x39 0x0>;
			dma-names = "fifo0", "fifo1";

			tsc {
				compatible = "ti,am3359-tsc";
			};

			adc {
				#io-channel-cells = <0x1>;
				compatible = "ti,am3359-adc";
				ti,adc-channels = <0 1 2 3 4 5 6>;
			};
		};

ActualLy I changed the status from "disabled" to "okay" and I added the ti,adc-channels descriptor to the adc section.

3. save the original DTB and compile the DTS:

   mv am335x-boneblack.dtb am335x-boneblack.dtb.orig
   dtc -O dtb -o am335x-boneblack.dtb -b 0 am335x-boneblack.dts

4. restart

5. check it:

   sysctl dev.ti_adc
   ....
   dev.ti_adc.0.ain.6.input: 0
   dev.ti_adc.0.ain.6.samples_avg: 0
   dev.ti_adc.0.ain.6.open_delay: 0
   dev.ti_adc.0.ain.6.enable: 0
   dev.ti_adc.0.ain.5.input: 0
   dev.ti_adc.0.ain.5.samples_avg: 0
   dev.ti_adc.0.ain.5.open_delay: 0
   dev.ti_adc.0.ain.5.enable: 0
   dev.ti_adc.0.ain.4.input: 0
   dev.ti_adc.0.ain.4.samples_avg: 0
   dev.ti_adc.0.ain.4.open_delay: 0
   dev.ti_adc.0.ain.4.enable: 0
   dev.ti_adc.0.ain.3.input: 0
   dev.ti_adc.0.ain.3.samples_avg: 0
   dev.ti_adc.0.ain.3.open_delay: 0
   dev.ti_adc.0.ain.3.enable: 0
   dev.ti_adc.0.ain.2.input: 0
   dev.ti_adc.0.ain.2.samples_avg: 0
   dev.ti_adc.0.ain.2.open_delay: 0
   dev.ti_adc.0.ain.2.enable: 0
   dev.ti_adc.0.ain.1.input: 0
   dev.ti_adc.0.ain.1.samples_avg: 0
   dev.ti_adc.0.ain.1.open_delay: 0
   dev.ti_adc.0.ain.1.enable: 0
   dev.ti_adc.0.ain.0.input: 3071
   dev.ti_adc.0.ain.0.samples_avg: 0
   dev.ti_adc.0.ain.0.open_delay: 0
   dev.ti_adc.0.ain.0.enable: 1
   dev.ti_adc.0.clockdiv: 2400
   dev.ti_adc.0.%parent: simplebus0
   dev.ti_adc.0.%pnpinfo: name=tscadc at 44e0d000 compat=ti,am3359-tscadc
   dev.ti_adc.0.%location: 
   dev.ti_adc.0.%driver: ti_adc
   dev.ti_adc.0.%desc: TI ADC controller
   dev.ti_adc.%parent: 

I can enable the ADC channels, and when connecting a 1002 mV DC source to AIN0 the reading was 2279, which is perfectly in line with 1002*4095/1800 = 2279.55.

Best regards

Rolf