Sylwester Nawrocki wrote: > Hi Sakari, Hi Sylwester, Thanks for the comments. > On 07/19/2011 03:37 PM, Sakari Ailus wrote: >> Hi all, >> >> The OMAP 3 ISP driver implements an HS_VS event which is triggered when >> the reception of a frame begins. This functionality is very, very likely >> not specific to OMAP 3 ISP so it should be standardised. >> >> I have a few patches to do that. Additionally the next expected buffer >> sequence number is provided with the event, unlike earlier. >> >> There are a few open questions, however, and this is why I'm sending the >> set as RFC. >> >> >> 1) Other frame synchronisation events. The CCDC block in the OMAP 3 ISP >> is able to trigger interrupts at two chosen lines of the image. These >> naturally can be translated to events. The driver uses both of them >> internally at specific points of the frame. Nevertheless, there might be >> some use for these in user space. Other hardware might implement a >> number of these which wouldn't be used by the driver itself, but I don't >> know of that at the moment. On the other hand high resolution timers are >> also available in user space, so doing timing based on ISP provided >> events is not quite as important as before --- as long as there's one >> frame based event produced at a known time, such as V4L2_EVENT_FRAME_START. > > I'm curious, have you perhaps tried to measure latency of such up calls > to a user space process? I mean this is going to be a real time stuff, > with HSYNC periods of 50 us order. Could a user space thread be receiving > such periodic events reliably ? From my experience I doubt this can work > reliably outside of an interrupt handler even with high priority real time > threads. > > V4L2_EVENT_FRAME_START event seems OK, but HSYNC events in user space > sound rather tricky to me :-) I think the user space could be interested in just one or two of these per frame, not for every line. But how to subscribe them --- if they are needed? Perhaps it'd be better to start with just one and add more once necessary? > Also HS_VS looks a bit more descriptive than FRAME_START for me. HS_VS doesn't really tell which one it is (horizontal or vertical), and we already have a VSYNC event but it's used for a different purpose. HS_VS is specific to the CCDC block and doesn't have that meaning in context of serial interfaces. This is why I proposed FRAME_START. > But unfortunately I can't come up with a better name, e.g. something like > V4L2_EVENT_FRAME_AV_START - frame active video start. Just in case in > future there are more specific events added. What additional information would AV add which isn't evident from FRAME_START? I admit that there could be differencies in terminology used in this area; terms that are meaningful to some might not be to others, or they could mean different things to them. Regards, -- Sakari Ailus sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx -- 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
