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Compute Module RUN pin

Posted: Thu Jan 16, 2020 12:07 pm
by jainprince
Hi Everyone,

I am using RPi compute module 3. There is a situation, where I want to disconnect the power of RPi. Is it acceptable, if I keep the LOW signal for long time(~ 30 min) on RUN pin(pin #177) to disconnect the power?

Thanks,
Prince

Re: Compute Module RUN pin

Posted: Thu Jan 16, 2020 12:14 pm
by trejan
Pulling the RUN pin low will hold the SoC in reset. It doesn't disconnect power.

I don't think there would be anything bad about doing this but you'll have to wait for a Raspberry Pi engineer to confirm.

Re: Compute Module RUN pin

Posted: Fri Jan 17, 2020 5:43 am
by aBUGSworstnightmare
I have no idea on your design, but if there would be the need for me to 'disconnect power' I would do this on the PMIC by using it's enable signal.
This will then really switch of power

Anyhow, holding the device in reset for a longer periid shouldn't be a problem.

Re: Compute Module RUN pin

Posted: Fri Jan 17, 2020 6:57 am
by jainprince
trejan wrote:
Thu Jan 16, 2020 12:14 pm
Pulling the RUN pin low will hold the SoC in reset. It doesn't disconnect power.

I don't think there would be anything bad about doing this but you'll have to wait for a Raspberry Pi engineer to confirm.
Hi, thanks for your response.
I am new to this forum, how can I get in touch with Raspberry Pi engineer?

Re: Compute Module RUN pin

Posted: Fri Jan 17, 2020 7:09 am
by jainprince
aBUGSworstnightmare wrote:
Fri Jan 17, 2020 5:43 am
I have no idea on your design, but if there would be the need for me to 'disconnect power' I would do this on the PMIC by using it's enable signal.
This will then really switch of power

Anyhow, holding the device in reset for a longer periid shouldn't be a problem.
Hi I designed in a way that, when the main power supply disconnects, RPi compute module running on battery power supply and also manages the power of other peripherals connected to compute module. And there might be a situation, when battery power is enough to boot the standalone RPi Compute Module, but when other peripherals connected to the module, starts draining the battery power, Compute Module power cycles as the power isn't enough now. And I have tested this, and it stuck in the power cycle loop. To avoid this situation, I have MSP430, this guy know when the power is not enough for Compute Module to power the other peripherals. In this case, MSP430 sends a low power signal to the RPI and RPi goes in shutdown state, and aftter 15-20(enough time for shutdown) seconds sending the low power signal to RPi, MSP430 keeps the RUN pin LOW to avoid the RPI to reboot again and again.

Please suggest, if you think, there could be a better design.

Thanks,
Prince

Re: Compute Module RUN pin

Posted: Fri Jan 17, 2020 2:59 pm
by gsh
Driving the RUN pin low for any length of time is fine, it will as previously said just hold the device in the reset state.