maemo.org - Talk - View Single Post - N900 will not allow USB OTG!

	joerg_rw	2010-04-08 , 16:41
	Posts: 2,222 \| Thanked: 12,651 times \| Joined on Mar 2010 @ SOL 3	#675

Originally Posted by blue_led

isp1707 & bq2415x marriage ...
until now ok for me .

fine :-)

Originally Posted by blue_led

a unwanted situation can be achieved when otg pin function is activated and a charger is attached: BQ chip start boost and depending wich source have higher voltage some current flow to other ( vbus > vcharger 200mA flow or vcharger > vbus nothing happen, Bq chip stop injecting power ), disconecting charger will lead to a looked loop BQ chip power the bus and isp chip detect vbus and asserting CHGR_DET sustain boost by BQ chip until battery is exhausted, because otg pin take precedence over i2c, there is no way to stop this situation. some hardware logic missing here.

Nope, we don't want to do this. From bq24150 manual:
In 32 second mode, when the OTG pin is in active status or the bit of operation mode (OPA_MODE) at control
register is set to 1, the bq24150/1 operates in boost mode and delivers the power to VBUS from the battery.

and
At the beginning of boost operation, the bq24150/1 starts a 32-second timer that can be reset by host through
I2C interface. Writing "1" to reset bit of TMR_RST in the control register resets the 32-second timer and
TMR_RST is automatically set to "0" after the 32-second timer is reset. To keep in boost mode, the host must
reset the 32-second timer repeatedly. Once the 32-second timer expires, the bq24150/1 turns off the boost
converter, enunciate the fault pulse in STAT pin and set fault status bits in status register. Fault condition is
cleared by POR or host control.

Originally Posted by blue_led

this can be the reason why nokia not implement host mode ?
there is no need to get vbus from isp chip or twl5030 and all configs of asics seems it can be made by software i think we can get host mode sometimes.

There's nothing I can find about OTG taking any precedence over this timer shutdown. So even if there *were* no better ways to stop VBUS boost, software always can stop updating the timer whenever we detect a hostmode USB detach, and of course also if we possibly read out chrg_det state (D+/- short) from 1707

So I don't yet see any reason beyond OTG compliance issues with USB-cert-authority for Nokia to not offer HOST MODE

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