On Wed, Feb 26, 2014 at 6:53 PM, Dr. H. Nikolaus Schaller hns@goldelico.com wrote:
- Barrel charger
i have read through the forum and seen that people still want a barrel charger. And I tried to find out why people insist of having it.
Apparently they see the (real) problem that you can't charge the Pyra any more while using the USB3.0 port in Host Mode (which means connecting an external hard disk or whatever).
There is only one standard solution - some Y-Cable with Micro-USB3.0 to Micro-USB3.0 and a charger connection. There are some USB3 Y cables - but they are built for a completely different scenario (connect a micro-usb3 hard disk to a USB3 PC host port and add more power through a second USB2 plug). So we would have to find someone to build such a cable for us.
At least on OMAP3+twl4030 combo this wouldn't work, unless you disconnect VBUS from twl4030 and control it externally.. As soon as you put musb into host mode it automatically drives the bus (musb hw sends commands to twl through ULPI (or whatever it was) bus automatically), and if somebody else is driving the bus the controller crashes and needs a powercycle.
Maybe things have improved now but I wouldn't be surprised if this scenario still wouldn't work at all.
I have another idea: we can use the Micro-USB planned for the Console UART (FTDI RS232 built in) as a secondary charger input. So we just have to make sure that either Micro-USB socket can drive the charger. I.e. this needs some FETs as power switches (ideal diode). This appears as if it can easily be solved.
This solution may also justify the higher cost of the second Micro-USB socket plus FTDI chip on board - instead of just having the 1.8V levels on some expansion connector and requiring an external level shifter. Because it gets a dual purpose and saves us from providing a very special cable.
I'd prefer this one too, perhaps even only allow charging though that port to avoid potential issues like I described above.
Some time ago ED told me he wanted a dedicated charging solution that the unit could be charged while it's off. Do we still have such goal?
GraÅžvydas