Re: [PATCH v2 1/7] v4l: Correct the ordering of LSBs of the 10-bit raw packed formats

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Hi Hans.

On 20/06/16 18:03, Hans Verkuil wrote:
On 06/20/2016 06:20 PM, Sakari Ailus wrote:
The 10-bit packed raw bayer format documented that the data of the first
pixel of a four-pixel group was found in the first byte and the two
highest bits of the fifth byte. This was not entirely correct. The two
bits in the fifth byte are the two lowest bits. The second pixel occupies
the second byte and third and fourth least significant bits and so on.

Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
As mentioned, this needs confirmation. I wonder, isn't this specified in the UVC
spec?

Regards,

	Hans
I'm assuming this is intended to be the same format as generated by many Bayer sensors. Those are defined in both the SMIA CCP2 (section 7.9), and MIPI CSI2 (section 11.4.4) specs. Whilst nominally restricted, they are both available via unofficial websites if you Google for them (I'm happy to send links, but didn't want to break mailing list rules by just posting them). CSI2 draft spec Figure 98 "RAW10 Data Transmission on CSI-2 Bus Bitwise Illustration" is probably the clearest confirmation of the bit ordering.

dcraw from http://www.cybercom.net/~dcoffin/dcraw/ can consume Raw10 via nokia_load_raw
    for (dp=data, col=0; col < raw_width; dp+=5, col+=4)
      FORC4 RAW(row,col+c) = (dp[c] << 2) | (dp[4] >> (c << 1) & 3);

And checking against the Raspberry Pi hardware simulator, the RAW10 parser code has
            for (i = 0; i < width; i++) {
               switch ((i + tile_x) & 3) {
                  case 0:  val = (buf[0] << 2) | (buf[4] & 3); break;
case 1: val = (buf[1] << 2) | ((buf[4] >> 2) & 3); break; case 2: val = (buf[2] << 2) | ((buf[4] >> 4) & 3); break;
                  default: val = (buf[3] << 2) | ((buf[4] >> 6) & 3);


All of those agree with Sakari's update that the first pixel's LSBits are in bits 1..0 of byte 5, 2nd pixel in bits 3..2, etc.

Regards,
  Dave
(working on the Pi CSI2 receiver V4L2 driver as there is now sufficient data in the public domain to do it. I'll be wanting these formats!)
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