Strange I2C/TWI Pullup Behaviour NRF53

RE: Strange I2C/TWI Pullup Behaviour NRF53

bsams — Sat, 07 Aug 2021 07:49:06 GMT

Hey Jorgen,

Yup, this is on our board.

Interesting, I assume that is what's going on, so this issue is probably closed.

Thanks,

Ben

RE: Strange I2C/TWI Pullup Behaviour NRF53

Jørgen Holmefjord — Thu, 05 Aug 2021 11:42:27 GMT

Hi,

[quote user="bsams"]in some modes the SCL/SDA lines are ties together with 20k[/quote]

Is this a mode on your board, or do you see the nRF5340 tie these lines together?

[quote user="bsams"]can I check if its because the peripheral is waiting for the line to go high again because it thinks the clock is being stretched[/quote]

Unfortunately, there is no events indicating that a clock stretch is ongoing, and there is also no status-register in the TWIM peripheral that will indicate this. I' not sure how else this could be checked.

[quote user="bsams"]and then timing out because its limiting the amount of clock stretching allowed[/quote]

As far as I know, there is no timeout/maximum allowed time for clock stretching.

Best regards,
Jørgen

RE: Strange I2C/TWI Pullup Behaviour NRF53

bsams — Wed, 04 Aug 2021 00:50:20 GMT

Hey Jorgen,

I think we've found the reason for the strange voltage, it looks like in some modes the SCL/SDA lines are ties together with 20k, so the internal pullups are active but the SCL is being pulled down by the SDA. It doesn't quite explain the timing change though, can I check if its because the peripheral is waiting for the line to go high again because it thinks the clock is being stretched, and then timing out because its limiting the amount of clock stretching allowed?

Thanks,

Ben

RE: Strange I2C/TWI Pullup Behaviour NRF53

Jørgen Holmefjord — Tue, 03 Aug 2021 14:55:33 GMT

[quote user="bsams"]Our FW and HW is custom, so it is difficult to port it to the DK.[/quote]

Ok, I still think it would be good to rule out board issues. Do you see the same behavior with I2C/TWI slave(s) connected to the bus?

[quote user="bsams"]My understanding of the drive strength is that it would affect the fall time, not the rise time?[/quote]

Yes, since it is configured with S0D1 by default (Standard '0'. disconnect '1'), I believe you are correct that it should not affect rise time.

RE: Strange I2C/TWI Pullup Behaviour NRF53

bsams — Mon, 02 Aug 2021 19:57:21 GMT

Hey Jorgen,

Our FW and HW is custom, so it is difficult to port it to the DK. My understanding of the drive strength is that it would affect the fall time, not the rise time?

Thanks,

Ben

RE: Strange I2C/TWI Pullup Behaviour NRF53

Jørgen Holmefjord — Fri, 30 Jul 2021 08:37:09 GMT

Thanks, yes it looks to be enabled.

Have you tried running the same firmware on a nRF5340 DK, to see if the signals look the same there?

You can also try to configure the GPIOs in High Drive (or even Extra high drive for P1.02/P1.03 pins), to see if that resolves the issue. You can use gpio_pin_configure() and the GPIO drive strength flags to configure drive strength of the GPIOs in NCS.

RE: Strange I2C/TWI Pullup Behaviour NRF53

bsams — Thu, 29 Jul 2021 18:59:43 GMT

Hi Jorgen,

The 0x50842A08 and 0x50842A0C registers are both 0x0000060c, which we believe means pullups enabled. We are using the normal zephyr nordic drivers.

Thanks,

Ben

RE: Strange I2C/TWI Pullup Behaviour NRF53

Jørgen Holmefjord — Thu, 29 Jul 2021 12:41:30 GMT

Hi,

Can you read the GPIO register configuration for the pins used with TWI peripheral from the debugger, to make sure that the pull resistors are actually enabled?

If you are using our drivers, this should be enabled by default, but it would be good to rule out this as the source of the issues.

Best regards,
Jørgen