What is Reset state of GPIOs on Raspberry Pi Compute Module 4?

Question

I want to use Raspberry Pi Compute Module 4 to control some 24V Outputs. I am using MAX14912 Driver.

I want to asure that Raspberry does not turn the output on during booting process.

According to BCM2711 Datasheet,at reset, all GPIO pins are configured as inputs (GPFSEL0 Register has reset value = 0x0) with pulldowns enabled (GPIO_PUP_PDN_CNTRL_REGX has value = 0x2).

I don't understand this sentence from Datasheet:

The Alternate function table also has the pull state which is applied after a power down.

What is the meaning of Pull column in this table? Does it mean that booter changes this values during the booting process (values from Device tree and config.txt)?

I measured the values at PINS after the system is up and I got values from the table.

But during booting i got this:

yellow - 3v3

green - GPIO4

orange - GPIO26

I understand it so:

All pins go high for couple of ms, than low (probably because of pulldowns) and than low/high (depending on Devicetree/config settings)

I don't understand why they all go high during.

Can someone explain it?

Answer 1

The table shows the default pulls which are applied by the hardware when the Pi is powered after being powered down.

Answer 2

On boot ALL pins are INPUT. A few (1-9 from memory) have pull-ups, others pull-down.

Shortly after power is applied pins are modified by Device Tree as configured in config.txt. It is possible to change pin state at this stage.