We are developing a board based on the i.MX7D Sabre and have two questions regarding reset/power up and power down.
1) According to the reference manual of the i.MX7D on pages 1047 and 1048 there are two reset schemes. One with internal and one with external PMIC. How are we supposed to configure the CPU such that it knows that we want to use the external one?
Our goal is to use a backup battery, therefore the CPU would be in SNVS Mode. As soon as external power is applied the CPU should turn on, without the need of an ONOFF Button. In my understanding the PMIC_ON_REQ is normally asserted LOW in SNVS Mode, is that correct? As long as the CPU keeps PMIC_ON_REQ low it is not possible to enable it externally. Then the only way is see to initiate boot-up with external circuitry is to disconnect PMIC_ON_REQ and use the external signal instead.
2) What happens when power is removed, without a "nice" software powerdown? Does the CPU enter SNVS Mode anyway?