I have done some further research. It seems that the tps65217.c mfd driver in the kernel sets the OFF bit (bit 7) in the PMIC STATUS register (offset 0xA) in order to make sure it shuts down all output voltages (including the RTC 1.8V supply from LDO2) when the system executes a power-down. This bit differentiates between OFF state and SLEEP state when the RTC in the main processor drives the POWER_EN signal low (the kernel sets the RTC alarm with a 1.5s timeout to disable POWER_EN as the final stage in powering down).
According to my reading of the TPS65217 spec it almost completely disables itself if OFF is set when POWER_EN is set low and this includes charging. If OFF is clear then it leaves the ability to charge enabled as well as keeping LDO2 enabled (to power the RTC). I did some experimentation and verified this. After booting I clear the OFF bit using i2cset and then power down. i2cset -y -f 0 0x24 0xa 0x00 sudo shutdown now The battery continues to charge after the system turns off (verified with an ammeter in series with the battery + lead). However there is also an additional ~15 mA load that is left on the battery when it is done charging. I see from the pocketbeagle schematic that a sn74lvc1g07 driver is taking power from the LDO2 output (VDD_RTC). However this chip should take much less than 1 mA so there is something else is taking power. I also notice that the OSD3358 SYS_VDD_3P3V (TL5209 regulator output) is also enabled. It is not normally enabled if the system is shutdown with the OFF bit set. I suspect circuitry in the Octavo module is consuming the extra power. This high quiescent current in exchange for charging when the system has been shut down is clearly a problem for a battery powered device. I will ask Octavo about this current as soon as my request for access to their forums is granted. It will be unfortunate if the high quiescent current is unavoidable because of a design decision made by Octavo. The decision to completely disable the PMIC on shut-down was clearly made to work around a bug in the version 1 TI AM3358 silicon (Advisory 1.0.17 in the errata) as well as design decisions by the Beaglebone Black team that could cause a potentially chip-damaging situation if the RTC was powered but the rest of the system was off. This is the "RTC-only mode" bug that you'll find documented, mainly on kernel threads. However by my reading of TI's errata and understanding of the pocketbeagle design, it seems that this should be able to work (as well as the RTC-only sleep mode) with the pocketbeagle. That would make the pocketbeagle even that much cooler. Perhaps I've missed something and would love to hear from anyone with additional information. Otherwise I guess this is just information for others in the future. Additional FYI: PMIC MFD Driver: https://github.com/beagleboard/linux/blob/7a920684860a790099061b67961d0b5ffa033fdf/drivers/mfd/tps65217.c RTC Driver: https://github.com/torvalds/linux/blob/master/drivers/rtc/rtc-omap.c -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/4fd8d165-48fd-485d-ae12-3739efaae627%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
