I tried to extend the maximum exposure time on camera V1. I have good and bad news.
The good news:
Lowering the register value 0x3036 (SC_CMMN_PLL_MULTIPLIER) extends the exposure time.
Increasing the upper nibble of 0x3035 (SC_CMMN_PLL_CTRL1) extend the exposure time by dividing all clocks.
Increasing the register value 0x380C and 0x380D (TIMING_HTS) extends the exposure time (max 0x1FFF).
This way I could take shots of about 25 s exposure with raspiraw.
0x3036 = 0x30
0x3035 = 0x81
0x380D = 0xFF
Also: line_time_ns in ov5647_modes.h set to 889026
Tha bad news:
The reproduceablilty of my experiments was really bad. I tried different or the same register settings on different days and got good and bad results with the same settings. Sometimes no images were captured, sometimes they were broken (missing lines). It seems that the timing for the start of a line is broken. Does anyone has an idea how to fix this?