TPS65950 Problem with LED control (for turning backlight on/off)

Hi Sabine,

I do not understand if your question is regarding software on OMAP or settings related to TPS65950.

Are you trying to use I2C to write the LED control registers on TPS65950?

Please elaborate your problem as much as possible so I can help further.

Regards,

Gandhar.

Hi Gandhar,

I'm not just yet sure whether the problem is in programming the I2C bus or in the TPS65950 settings.

I have no logic analyzer available, so it is not possible for me to check if SDA and SCL are driving the signals I'd expect.

Yes, I am using the I2C1 component to access the LED control registers. Is there any extremely simple one-register-command on the TPS65950 which allows me to ensure definitely if my writing routine works correctly?

I currently use the programming example to activate LEDA with 50% brightness. The used settings are the following:

    VIBRA_CTL (slave address 0x49) =  0

    LEDEN (slave address 0x4A) = 0x11

    PWMAON (slave address 0x4A) = 63

    PWMAON (slave address 0x4A) = 127   

Best regards,

Sabine

Hi Gandhar,

... I've written the I2C-read method using the flow chart in figure 18-30 of the OMAP35x Application Processor TRM (Master Receiver Mode, Polling Method). But reading a register does not work, the I2C status register is always 0.

However, if it worked but reading did not deliver the correct value, I could not know if the I2C-read or the I2C-write routine was the problem, could I?

I also tested the example of page 496, it does not change anything.

Best regards,

Sabine

Hi,

You seem to have problem with your driver. It is best if you can download some code from the open community and try to use that instead of creating your own driver. You should be able to port that into your code.

Regards,

Gandhar.

Hi,

I seem to have the same problem. I am using the beagleboard. However, I am able to write and read the same vales from the register over i2c.

i2c_readbyte(0x4a,0xEE,&CC); //Returns 00
kprintf("LEDEN %d\n ",CC);

i2c_writebyte(0x49,0x45,0x0);
i2c_writebyte(0x4A,0xEE,0x03);
i2c_writebyte(0x4A,0xef,63);
i2c_writebyte(0x4A,0xf0,127);

 i2c_readbyte(0x4a,0xEE,&CC); //Returns 03
kprintf("LEDEN %d\n ",CC);

What might be wrong?

@ SabineKäß: How did you get around your problem?

Thank you

Not sure I understand your problem. You write 0x03 to physical address 0xEE and you read back the correct value.

I might be missing something or interpreting your problem differently. 

That is true, I read the correct value, but the LED remains as off as ever. :-(

Thank you.

May be your PWM setting is set to keep it off all the time. Follow steps in section 8.5 and probe the output. I am assuming external connections from LED to VBAT is ok.

Thanks :-) I got it working

The sequence that worked is 

i2c_readbyte(0x4a,0xEE,&CC);
kprintf("LEDEN %d\n ",CC);

i2c_writebyte(0x49,0x45,0x0); //Vibra_CTRL
i2c_writebyte(0x4A,0xEE,0x22); //LEDEN & PWMB
i2c_writebyte(0x4A,0xf1,63); //PWM ON
i2c_writebyte(0x4A,0xf2,127); //PWM Off

i2c_readbyte(0x4a,0xEE,&CC);
kprintf("LEDEN %d\n ",CC);

Reading through the datasheet, I was of the impression that enabling the PWM was optional if I wanted the LED on without intensity modulation. However, the LED just does not glow if the LEDEN[PWMB] is not set. I will have to set the PWM on with a 100% dutycycle.

Makes me wonder what is the point of the PWMB bit in the LEDEN register? Have I got something wrong? Is there a way to have the LED on without bothering with the PWM?

Thank you.