Am Di 6. Mai 2008 schrieb Werner Almesberger: > [ Cc:s trimmed ] > > [EMAIL PROTECTED] wrote: > > Now if we detect there's not 0volt but instead there's 5volt on the ID-pin > > while we're applying 0volt to internal R, we got a new info about what's > > plugged to our USB-receptacle, and we might ->>route this 5volt to our > > PMU<<-. > > So the proposal is to make a Y-cable that connects ID to VBUS. The cable > would not be permanently attached to any devices (i.e., a fixed charger > cable). The connectors would be A-A/B(1)-B(2), where A goes to a host > providing power or our charger, A/B(1) goes to the Neo, and B(2) goes to > a device that may in turn be OTG-capable. Correct so far ? > > Micro-USB_1_01.pdf, page 10, below table 4-2 says: > > | The ID pin on a Micro-A plug shall be connected to the GND pin. > > So the ID = VBUS arrangement would violate this. > > Of course, a Y-cable would violate Micro-USB 1.01 as well :-) > > | No other types of cables are allowed by either the USB specification, > | or by the OTG supplement. > > (Page 8.) > > The Micro-USB is silent about the use of ID in receptacles, particularly > on the A-side. If we make a worst-case assumption that ID is just > connected to GND, we could possibly damage the device. > > In order to avoid this sort of problem, ID on the A-side would have to > be unconnected, and the connection between ID and VBUS would have to be > made further down the cable, i.e., inside the A/B(1) connector. > > | The ID pin on a Micro-B plug is not connected or is connected to ground > | by a resistance of greater than Rb_PLUG_ID (100kOhm MIN). > > So actually having 5V on ID on A/B(1) or even B(2) shouldn't damage a > compliant device. (I.e., if the cable is used with some device that's > not a Neo.) > > For compatibility with OTG, B(2).ID would have to be connected to GND. > So the overall connections would be roughly as follows: > > A A/B(1) B(2) > > VBUS -----+----- VBUS ----------- VBUS > ID -- \---- ID -- /----- ID > GND ----------- GND -----+----- GND > > Is this what you had in mind ? Since the Neo side receptacle would have > to be AB, what would the plug be - A or B ? > > BTW, regarding doing measurements through GPIO+R instead of rail+R, > I think this is in general good practice giving one flexibility for > usually little cost. > > - Werner >
Yep, for the first look it's about what I've been thinking of. The ID pin on A and B(2) could be left open completely I think. Neo would detect +5V on ID as identical to GND for initiating logic hostmode, and as charger for power management. The most minimal solution for the nasty problem. Only there is a chance to burn other devices (ID to GND low Z) - too bad :-( User has to build the cable himself, so he mustn't blame me/OM ;-) I wouldn't suppose to use any other power source than a dedicated USB-charger /jOERG _______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
