I am confused by the number "172" in em28xx-core.c, function em28xx_isoc_video(),
When we acquire the bottom field, we first see if everything is correct using these states:
+++++++++++++++++++++++++++++++++++++++++++++++++++
if (!(*f)->top_field) {
(*f)->state = F_ERROR;
em28xx_isocdbg ("unexpected begin of bottom field; discarding it");
} else if ((*f)-> fieldbytesused < dev->field_size - 172) {
(*f)->state = F_ERROR;
em28xx_isocdbg ("dropping incomplete top field (%i missing bytes)",
dev->field_size-(*f)->fieldbytesused);
} else {
(*f)->top_field = 0;
(*f)->fieldbytesused = 0;
}
++++++++++++++++++++++++++++++++++++++++++++++++++++
but why do we need minus 172 in the second branch??????
I think when we finish the top field grabbing, (*f)->fieldbytesused =dev->field_size,
but the code seems not, (*f)->fieldbytesused = dev->field_size, why???
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