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awilliam
GitHub Repository: awilliam/linux-vfio
 Path: blob/master/drivers/media/video/gspca/pac_common.h
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/*

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 * Pixart PAC207BCA / PAC73xx common functions

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 *

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 * Copyright (C) 2008 Hans de Goede <[email protected]>

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 * Copyright (C) 2005 Thomas Kaiser [email protected]

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 * Copyleft (C) 2005 Michel Xhaard [email protected]

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 *

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 * V4L2 by Jean-Francois Moine <http://moinejf.free.fr>

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 *

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 * This program is free software; you can redistribute it and/or modify

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 * it under the terms of the GNU General Public License as published by

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 * the Free Software Foundation; either version 2 of the License, or

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 * (at your option) any later version.

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 *

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 * This program is distributed in the hope that it will be useful,

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 * but WITHOUT ANY WARRANTY; without even the implied warranty of

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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

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 * GNU General Public License for more details.

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 *

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 * You should have received a copy of the GNU General Public License

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 * along with this program; if not, write to the Free Software

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 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

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 *

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 */

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/* We calculate the autogain at the end of the transfer of a frame, at this

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   moment a frame with the old settings is being captured and transmitted. So

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   if we adjust the gain or exposure we must ignore atleast the next frame for

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   the new settings to come into effect before doing any other adjustments. */

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#define PAC_AUTOGAIN_IGNORE_FRAMES	2

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static const unsigned char pac_sof_marker[5] =

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		{ 0xff, 0xff, 0x00, 0xff, 0x96 };

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/*

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   The following state machine finds the SOF marker sequence

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   0xff, 0xff, 0x00, 0xff, 0x96 in a byte stream.

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	   +----------+

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	   | 0: START |<---------------\

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	   +----------+<-\             |

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	     |       \---/otherwise    |

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	     v 0xff                    |

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	   +----------+ otherwise      |

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	   |     1    |--------------->*

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	   |          |                ^

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	   +----------+                |

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	     |                         |

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	     v 0xff                    |

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	   +----------+<-\0xff         |

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	/->|          |--/             |

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	|  |     2    |--------------->*

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	|  |          | otherwise      ^

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	|  +----------+                |

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	|    |                         |

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	|    v 0x00                    |

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	|  +----------+                |

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	|  |     3    |                |

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	|  |          |--------------->*

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	|  +----------+ otherwise      ^

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	|    |                         |

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   0xff |    v 0xff                    |

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	|  +----------+                |

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	\--|     4    |                |

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	   |          |----------------/

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	   +----------+ otherwise

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	     |

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	     v 0x96

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	   +----------+

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	   |  FOUND   |

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	   +----------+

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*/

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static unsigned char *pac_find_sof(u8 *sof_read,

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					unsigned char *m, int len)

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{

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	int i;

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	/* Search for the SOF marker (fixed part) in the header */

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	for (i = 0; i < len; i++) {

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		switch (*sof_read) {

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		case 0:

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			if (m[i] == 0xff)

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				*sof_read = 1;

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			break;

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		case 1:

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			if (m[i] == 0xff)

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				*sof_read = 2;

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			else

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				*sof_read = 0;

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			break;

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		case 2:

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			switch (m[i]) {

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			case 0x00:

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				*sof_read = 3;

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				break;

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			case 0xff:

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				/* stay in this state */

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				break;

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			default:

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				*sof_read = 0;

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			}

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			break;

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		case 3:

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			if (m[i] == 0xff)

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				*sof_read = 4;

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			else

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				*sof_read = 0;

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			break;

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		case 4:

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			switch (m[i]) {

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			case 0x96:

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				/* Pattern found */

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				PDEBUG(D_FRAM,

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					"SOF found, bytes to analyze: %u."

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					" Frame starts at byte #%u",

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					len, i + 1);

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				*sof_read = 0;

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				return m + i + 1;

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				break;

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			case 0xff:

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				*sof_read = 2;

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				break;

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			default:

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				*sof_read = 0;

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			}

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			break;

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		default:

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			*sof_read = 0;

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		}

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	}

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	return NULL;

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}

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