Hi Javier, On Thursday 26 May 2011 13:31:37 javier Martin wrote: > OK, I think I've found the problem with the power management. > > As it is stated in mt9p031 datasheet [3] p 59, a sequence involving > [VAA,VAA_PIX,VDD_PLL], [VDD,VDD_IO], [Reset] and [Ext Clk] must be > followed in order to properly power up or down the sensor. > > If we take a look to the LI-5M031 schematic[1] and Beagleboard xM > schematic [2] we'll notice that voltages are connected as follows: > > [VDD] (1,8V) <--- V2.8 <--- CAM_CORE <--- VAUX3 TPS65950 > [VDD_IO (VDDQ)] (1,8V) <--- V1.8 <--- CAM_IO <--- VAUX4 TPS65950 > [VAA, VAA_PIX, VDD_PLL] (2,8V) <---| U6 |<-- V3.3VD <-- HUB_3V3 <--| > U16 | enabled by USBHOST_PWR_EN <-- LEDA TPS65950 > > VAUX3 (VDD) and VAUX4 (VDD_IO) are fine, they are only used for > powering our camera sensor. However, when it comes to the analog part > (VAA, VAA_PIX...), it is got from HUB_3V3 which is also used for > powering USB and ethernet. *sigh* Why do hardware designers do things like that, really ? > If we really want to activate/deactivate regulators that power mt9p031 > we need to follow [3] p59. However, for that purpose we need to ensure > that a call to regulator_enable() or regulator_disable() will really > power on/off that supply, otherwise the sequence won't be matched and > the chip will have problems. > > Beagleboard xM is a good example of platform where this happens since > HUB_3V3 and thus (VAA, VAA_PIX, etc...) cannot be deactivated since it > is being used by other devices. But there could be others. > > So, as a conclusion, and in order to unblock my work, my purpose for > power management in mt9p031 would be the following: > - Drop regulator handling as we cannot guarantee that power on > sequence will be accomplished. > - Keep on asserting/de-asserting reset which saves a lot of power. > - Also activate/deactivate clock when necessary to save some power. > > I'm looking forward to read your comments on this. Even if you keep the sensor powered all the time, how do you ensure that VAUX3 is available before HUB_3V3 when the system is powered up ? > [1] https://www.leopardimaging.com/uploads/li-5m03_camera_board_v2.pdf > [2] http://beagle.s3.amazonaws.com/design/xM-A3/BB-xM_Schematic_REVA3.pdf > [3] http://www.aptina.com/products/image_sensors/mt9p031i12stc/ -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
