Hi all,
I need help from someone who knows more about CSI driver. I want to use
16bit YUV422 capture mode for CSI0. However, I have found that this mode is
not supported in kernel 3.4, so I went on to hack the kernel.
My system is Allwinner A20 on Olinuxino Micro board.
First problem is that 16-bit mode is never applied, even if csi_if is set
to '1' in the fex file and define d8..d15. The problem is in
sun4i_csi_core.h:
/*
* input data format
*/
typedef enum tag_CSI_INPUT_FMT
{
CSI_RAW=0, /* raw stream */
CSI_BAYER, /* byer rgb242 */
CSI_CCIR656, /* ccir656 */
CSI_YUV422, /* yuv422 */
}__csi_input_fmt_t;
So, in this enum, CSI_YUV422 is always set to 3, and as so written to the
CSI0_CFG register. The correct mode for 16bit is 4, so the simplest way is
to change the enum like:
/*
* input data format
*/
typedef enum tag_CSI_INPUT_FMT
{
CSI_RAW=0, /* raw stream */
CSI_BAYER, /* byer rgb242 */
CSI_CCIR656, /* ccir656 */
CSI_YUV422=4, /* yuv422 */
// CSI_YUV422, /* yuv422 */
}__csi_input_fmt_t;
However, surprise, surprise, this doesn't work (no capture at all). The
second problem is that YUV422 16bit is supposed to be using embedded sync
codes, unlike YUV422 8bit mode, which is not and much like bt.656 (CCIR656)
mode, which by the way is not supported at all in the driver (just a bunch
of todos). So, I have enabled embedded sync codes for my sensor system
(sensor + fpga, so it's quite flexible), but there was a third problem -
unlike 8bit mode, 16bit mode is latched on the opposite edge, so you need
to define CSI_FALLING as clock polarity for whichever sensor driver you're
using (or simply invert pixel clock), otherwise CSI will not capture
anything (as the sync codes are messed up when latched on the wrong edge).
However, even though now I am successfully capturing the signal coming from
the camera, I am only capturing the lower 8 bits - I can't get the upper 8
bits no matter what I do. I am currently suspecting DMA (seems likely)
and/or GPIO config for 16bits (this also seems strange - I couldn't find
any references to csi_d* vars from fex file in the entire kernel), but
other than that I am running out of ideas quite fast. Debug up to this
point was already hard enough, as there is no clear documentation from
Allwinner about this at all (I have searched through their entire line-up -
starting from A10, up to A31).
If someone knows something, please share - if I had some more
documentation, I would have probably already made the whole thing work, but
this way I feel like I am more and more just trying out some things blindly
than actually solving problems...
So please help if you know more. If I get further, I will post my progress
back of course.
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