AMC6821: Linux Device Driver

Shubhakara P S

Part Number: AMC6821

Hii,

I am trying to use the AMC6821 Linux Device Driver, for Controlling FAN Speed, As per the Kernel Documentation I have Followed the steps on how to insmod this module and here are the steps I have did.

1. Added Device Tree Binding For AMC6821 which is as follows.

i2c-mux@74 {
               compatible = "nxp,pca9548";
               #address-cells = <0x1>;
               #size-cells = <0x0>;
               reg = <0x74>;

              i2c@5 {
                                        #address-cells = <0x1>;
                                        #size-cells = <0x0>;
                                        reg = <0x5>;

                                       amc6821@18 {
                                         compatible = "ti,amc6821";
                                         reg = <0x18>;
                                     };
                                 };

2. When I am trying to Load the Module (amc6821.ko file) I am getting the following errors

root@zcu102-zynqmp:~# insmod amc6821.ko init=1 pwminv=1;
[ 5.635243] amc6821 12-0018: Configuration register write error, aborting.
[ 5.642122] amc6821: probe of 12-0018 failed with error -5

Which means the AMC6821 Chip was Not Initialising Properly, And may I know the Reason for the same ??

Regards,

Shubhakara P S

over 5 years ago

0 David Vaseliou over 5 years ago

TI__Expert 6820 points

Hi Shubhakara,

Let me reach out to our Linux team for information on this.

Thanks,

0 David Vaseliou over 5 years ago in reply to David Vaseliou

TI__Expert 6820 points

Hi Shubhakara,

Can you send a oscilloscope waveform of the I2C transaction? Also can you send me schematic of the device.

Thanks,

0 Shubhakara P S over 5 years ago

Prodigy 240 points

Hii,

Well this is due to the problem of frequency setting for SCLK , AMC6821 Supports Max clock Frequency of 100 KHZ, and we have changed the Master Clock Frequency from 400KHZ to 100KHZ, well as off now we are getting the clock and the device is probed successfully.

And we are checking the PWM_OUT Signal in Oscilloscope at J5 (11), we are not getting any waveform at this pin.

I think so the driver initialises the chip by default in Software DCY Mode we did not change anything in the driver configuration just we have loaded the Driver using insmod amc6821.ko with init=1

And we got the following sysfs attributes in /sys/class/hwmon/hwmon20

device pwm1_auto_channels_temp temp1_crit_alarm temp2_crit_alarm
fan1_div pwm1_auto_point1_pwm temp1_input temp2_fault
fan1_fault pwm1_auto_point2_pwm temp1_max temp2_input
fan1_input pwm1_auto_point3_pwm temp1_max_alarm temp2_max
fan1_max pwm1_enable temp1_min temp2_max_alarm
fan1_min subsystem temp1_min_alarm temp2_min
name temp1_auto_point1_temp temp2_auto_point1_temp temp2_min_alarm
of_node temp1_auto_point2_temp temp2_auto_point2_temp uevent
power temp1_auto_point3_temp temp2_auto_point3_temp
pwm1 temp1_crit temp2_crit

When I do cat pwm1_enable , it shows 1 which means in the driver code case 1 is executed

long val;
        int config = kstrtol(buf, 10, &val);
        if (config)
                return config;

        mutex_lock(&data->update_lock);
        config = i2c_smbus_read_byte_data(client, AMC6821_REG_CONF1);
        if (config < 0) {
                        dev_err(&client->dev,
                        "Error reading configuration register, aborting.\n");
                        count = config;
                        goto unlock;
        }

        switch (val) {
        case 1:
                config &= ~AMC6821_CONF1_FDRC0;
                config &= ~AMC6821_CONF1_FDRC1;
                break;

So, If Both the FDRC0 and FDRC1 Bit is 0
0 0 ---> Software DCY control. Host writes DCY register to set the PWM duty cycle directly.

So, we have setted the pw1_enable to 1 and we are trying change the pwm1 file , by writing the values from 0 to 255, But we are Not getting any waveforms on PWM_OUT(J5-11) Pin.

Regards,

Shubhakara P S

0 David Vaseliou over 5 years ago in reply to Shubhakara P S

TI__Expert 6820 points

Hi Shubhakara,

Can you please send me your schematic and a register dump of your settings?

Thanks,

0 Shubhakara P S over 5 years ago

Prodigy 240 points

Hii,

Here is the Register Dump printed in init_client function at Boot Up

[14418.411172] config @ addr: 0x04 AMC6821_REG_CONF4: 0x88
[14418.416340] after "config |= AMC6821_CONF4_MODE"
[14418.420929] config @ addr: 0x04 AMC6821_REG_CONF4: 0x88
[14418.426878] config @ addr: 0x3F AMC6821_REG_CONF3: 0x03
[14418.432030] amc6821 12-0018: Revision 3
[14418.435840] after "config &= ~AMC6821_CONF3_THERM_FAN_EN"
[14418.441223] config @ addr: 0x3F AMC6821_REG_CONF3: 0x03
[14418.447305] config @ addr: 0x01 AMC6821_REG_CONF2: 0x01
[14418.452451] after "config &= ~AMC6821_CONF2_RTFIE"
[14418.457219] after "config &= ~AMC6821_CONF2_LTOIE"
[14418.461994] after "config &= ~AMC6821_CONF2_RTOIE"
[14418.466768] config @ addr: 0x01 AMC6821_REG_CONF2: 0x01
[14418.472856] config @ addr: 0x00 AMC6821_REG_CONF1: 0x09
[14418.478002] after "config &= ~AMC6821_CONF1_THERMOVIE"
[14418.483123] after "config &= ~AMC6821_CONF1_FANIE"
[14418.487897] after "config |= AMC6821_CONF1_START"
[14418.492586] config @ addr: 0x00 AMC6821_REG_CONF1: 0x09
[14418.497793] value of PWMINV After Making 1 is 9
[14418.503052] pwminv: 0x1
[14418.505415] config @ addr: 0x00 AMC6821_REG_CONF1: 0x09

0 David Vaseliou over 5 years ago in reply to Shubhakara P S

TI__Expert 6820 points

Hi Shubhakara,

I am able to see the PWM signal with those settings on my set up. Can you please send me your schematic. Also, to what value is register 0x22 set?

Thanks,

0 David Vaseliou over 5 years ago in reply to David Vaseliou

TI__Expert 6820 points

Shubhakara,

Thanks for the information from these threads e2e.ti.com/.../871574 and https://e2e.ti.com/support/sensors/f/1023/t/871579 .

Please check jumpers W7 and J5 pin 9-10 connection for PWMOUT Pull-up.

Do you see the PWMOUT waveform without the fan connected to the EVM?

Thanks,

0 Shubhakara P S over 5 years ago

Prodigy 240 points

Hi David,

W7 jumper is connect for position 1 - 2.
In J5 jumper 9 - 10 are connected

We are testing this TI's AMC6821 EVM with Xilinx ZCU102 board (having zynq ultrascale+ on it) which works at 3.3v. Therefore AMC6821 EVM is jumpered to work at 3.3v
We are able to see 3.3v VDD on Pin-6. But on PWM-OUT Pin-1 we always observe fixed 1v all the time on the CRO. Never seen any waveform, irespective of what values we try writing to DCY register and other configuration registers.

0 David Vaseliou over 5 years ago in reply to Shubhakara P S

TI__Expert 6820 points

Hi Shubhakara,

For clarification, when you say "observe fixed 1v" do you mean fixed high (3.3V) or is it the pin pulling the pull-up voltage down to 1V?

Can you check the status registers 0x02 and 0x03 to make sure there are no faults that might cause PWMOUT to stay high?

Also, can you try to toggle the PWMOUT by using 0x00 bit 3.

Thanks,

0 Shubhakara P S over 5 years ago

Prodigy 240 points

HI David,

For clarification, when you say "observe fixed 1v" do you mean fixed high (3.3V) or is it the pin pulling the pull-up voltage down to 1V?

Yes, it is Fixed 1v, Don't know whether it is the PIn pulling the Pull-up voltage down to 1V, just we have observed the waveform at PWM_OUT Pin , it is always constant 1V.

Okay, let me read out these Registers , and get Back to you.

Regards,

Shubhakara P S

0 Shubhakara P S over 5 years ago

Prodigy 240 points

Hi David,

Can you check the status registers 0x02 and 0x03 to make sure there are no faults that might cause PWMOUT to stay high?

Status Registers 0x02 and 0x03 are set to Default (0x00, 0x00) , We are not modifying anything in these registers, as you can see in the driver code snippet below

drivers/hwmon/amc6821.c

#define AMC6821_REG_STAT1 0x02
#define AMC6821_REG_STAT2 0x03

data->stat1 = i2c_smbus_read_byte_data(client,
                        AMC6821_REG_STAT1);
                data->stat2 = i2c_smbus_read_byte_data(client,
                        AMC6821_REG_STAT2);

Also, can you try to toggle the PWMOUT by using 0x00 bit 3. ?

Yes, we are toggling out this pin (PWMINV) , By default it will be 0 , and we are inverting it, while loading the kernel module as follows.

insmod amc6821.ko init=1 pwminv=1

when pwminv=1 and in the driver snippet code

if (pwminv)
                        config |= AMC6821_CONF1_PWMINV;
                else
                        config &= ~AMC6821_CONF1_PWMINV;

Regards,

Shubhakara P S

0 Shubhakara P S over 5 years ago

Prodigy 240 points

Hi David,

Good Morning, I am waiting For Your Response !

Regards,

Shubhakara P S

0 Shubhakara P S over 5 years ago

Prodigy 240 points

Hi David,

For clarification, when you say "observe fixed 1v" do you mean fixed high (3.3V) or is it the pin pulling the pull-up voltage down to 1V?

When i say "observe fixed 1v", i am talking about reading voltage value of 1 volt on oscilloscope (not the logic level of 1). So yes, it will be correct to say that the pin is puling the pull-up voltage down to 1V. On J5, 9 - 10 shorted (connected) and 11 - 12 are left open.
When i measure the terminal of R13 that is connected to VDD, it measures 3.3V but on the terminal of R13 connected to pin 10 of J5 measures 1V.

Thanks & Regards,

Shubhakara P S

0 David Vaseliou over 5 years ago in reply to Shubhakara P S

TI__Expert 6820 points

Hi Shubahakara,

Please check the pull-up voltage and the jumpers on your board. This pin is open drain so I do not expect the voltage to be much less than the pull-up voltage. I am sending you a picture of my EVM configuration for reference.

Thanks,

0 Shubhakara P S over 5 years ago

Prodigy 240 points

Hi David,

Thank you so much for your Valuable Support , The issue had been Solved, The chip had gone Bad, We replaced one more chip then it works fine.

Thanks & Regards,

Shubhakara P S

0 David Vaseliou over 5 years ago in reply to Shubhakara P S

TI__Expert 6820 points

Shubhakara,

I am glad your set up is now working. Thanks for posting to the e2e!

Thanks,

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AMC6821: Linux Device Driver