Took a closer look at these registers in 5D3 and matched them with some firmware strings:
1080p24 1080p25 1080p30 1080p24->40 1080p25->40 720p50 720p60 x5 photo full-res LV
0x8178, 0x8196 PowerSaveTiming on 1321 1321 1321 1321 1321 695 695 1383 unused 3933
0x8179, 0x8197 PowerSaveTiming off 2193 1924 1738 1418 1424 924 828 1486 unused 3945
0x82F8 ReadOutTiming 1320 1320 1320 1320 1320 694 694 1382 unused 3932
0x82F9 set to TimerB - 1 2274 1999 1819 1499 1499 999 909 1555 unused 4020
FPS timer A 440 480 440 400 400 480 440 518 792 792
FPS timer B 2275 2000 1820 1500 1500 1000 910 1556 3958 4094
C0F06800 - C0F06804 [ 2080 x 1319 ] [ 2080 x 693 ] 3744x1381 5936x3949 5936x3931
The PowerSaveTiming registers, if misconfigured, are causing artifacts
like this. Time units are from 0 to FPS timer B - 1; this covers a complete LiveView frame. For each timer B increment, one line is read out (well, 80D reads two lines per tick, but that's another story).
If the powersave timing registers are set to some value lower than desired vertical resolution, you will not get valid data on the lines in-between. Example: if you set the "on" register to 1320 / 2 = 660, and the "off" register to something a bit higher, e.g. 670, you'll get a thin bar of missing data somewhere in the middle of the image. Canon firmware enables powersaving after one frame was fully read out, until the next frame. That means, the "on" timing is just a bit higher than the desired vertical resolution (including black bars etc) and the "off" timing is just a bit lower than FPS timer B (aka total frame duration, one unit being timer A / MainClock, e.g. 440 / 24MHz = 18.33 microseconds).
If you set both powersave registers to 0, it seems to work just fine, although it might run a little hotter than usual.
TODO: now that we know their meaning, these registers should be set properly to reduce power consumption. In the current source, these were set by trial and error, so there is room for improvement.
Register 0x82F8 affects the image: if you set it to 660 (i.e. nrzi_encode(660) = 0x3de), the bottom half of the image will get darker, with some artifacts near highlights.
Register 0x82F9 had no obvious effect in my quick tests.
On 6D and 700D, the powersave timing registers are 8172/8178 (on), 8173/8179 (off), 82f8 (readout timing), 82f9 (unknown). On 700D, register 82B6 is set to powersave timing "on" - 2. All of them are NRZI-encoded.
