Pavel Machek wrote: > Hi! > >> +Protocol Example A >> +------------------ >> + >> +Here is what a minimal event sequence for a two-contact touch would look >> +like for a type A device: >> + >> + ABS_MT_POSITION_X x[0] >> + ABS_MT_POSITION_Y y[0] >> + SYN_MT_REPORT >> + ABS_MT_POSITION_X x[1] >> + ABS_MT_POSITION_Y y[1] >> + SYN_MT_REPORT >> + SYN_REPORT > ... >> -Usage >> ------ >> +Here is the sequence after lifting the first contact: >> + >> + ABS_MT_POSITION_X x[1] >> + ABS_MT_POSITION_Y y[1] >> + SYN_MT_REPORT >> + SYN_REPORT > > ... > >> +Protocol Example B >> +------------------ >> + >> +Here is what a minimal event sequence for a two-contact touch would look >> +like for a type B device: >> + >> + ABS_MT_SLOT 0 >> + ABS_MT_TRACKING_ID 45 >> + ABS_MT_POSITION_X x[0] >> + ABS_MT_POSITION_Y y[0] >> + ABS_MT_SLOT 1 >> + ABS_MT_TRACKING_ID 46 >> + ABS_MT_POSITION_X x[1] >> + ABS_MT_POSITION_Y y[1] >> + SYN_REPORT >> + >> +Here is the sequence after moving contact 45 in the x direction: >> + >> + ABS_MT_SLOT 0 >> + ABS_MT_POSITION_X x[0] >> + SYN_REPORT > > With this proposed system, protocol A is *very* different from > protocol B. Is there way to make them more similar? Hello, unfortunately, the two protocols are different for a reason. Given the point of the type B protocol, to reduce bandwidth and accommodate filtering in the input core, the major difference is that type A receivers always expect all data between synchronizations, whereas type B devices never send all data. This alone means a receiver wishing to support both type of streams will need to know what type of stream to expect. This is accomplished by the presence of ABS_MT_SLOT. Secondly, in order to not break the established semantics of events, ABS_MT_SLOT is used instead SYN_MT_REPORT. This also makes type B devices in type A applications stop working in a somewhat graceful fashion. The usage of SYN_MT_REPORT versus ABS_MT_SLOT is the only syntactic difference between the protocols, and it stems from the different interpretation of what comes through the wire. IMHO, it means the way the type B protocol is formulated is the smallest possible change that accommodates the required effect. Thanks, Henrik -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
