1.. SPDX-License-Identifier: GPL-2.0
2
3The cx2341x driver
4==================
5
6Non-compressed file format
7--------------------------
8
9The cx23416 can produce (and the cx23415 can also read) raw YUV output. The
10format of a YUV frame is 16x16 linear tiled NV12 (V4L2_PIX_FMT_NV12_16L16).
11
12The format is YUV 4:2:0 which uses 1 Y byte per pixel and 1 U and V byte per
13four pixels.
14
15The data is encoded as two macroblock planes, the first containing the Y
16values, the second containing UV macroblocks.
17
18The Y plane is divided into blocks of 16x16 pixels from left to right
19and from top to bottom. Each block is transmitted in turn, line-by-line.
20
21So the first 16 bytes are the first line of the top-left block, the
22second 16 bytes are the second line of the top-left block, etc. After
23transmitting this block the first line of the block on the right to the
24first block is transmitted, etc.
25
26The UV plane is divided into blocks of 16x8 UV values going from left
27to right, top to bottom. Each block is transmitted in turn, line-by-line.
28
29So the first 16 bytes are the first line of the top-left block and
30contain 8 UV value pairs (16 bytes in total). The second 16 bytes are the
31second line of 8 UV pairs of the top-left block, etc. After transmitting
32this block the first line of the block on the right to the first block is
33transmitted, etc.
34
35The code below is given as an example on how to convert V4L2_PIX_FMT_NV12_16L16
36to separate Y, U and V planes. This code assumes frames of 720x576 (PAL) pixels.
37
38The width of a frame is always 720 pixels, regardless of the actual specified
39width.
40
41If the height is not a multiple of 32 lines, then the captured video is
42missing macroblocks at the end and is unusable. So the height must be a
43multiple of 32.
44
45Raw format c example
46~~~~~~~~~~~~~~~~~~~~
47
48.. code-block:: c
49
50	#include <stdio.h>
51	#include <stdlib.h>
52	#include <string.h>
53
54	static unsigned char frame[576*720*3/2];
55	static unsigned char framey[576*720];
56	static unsigned char frameu[576*720 / 4];
57	static unsigned char framev[576*720 / 4];
58
59	static void de_macro_y(unsigned char* dst, unsigned char *src, int dstride, int w, int h)
60	{
61	unsigned int y, x, i;
62
63	// descramble Y plane
64	// dstride = 720 = w
65	// The Y plane is divided into blocks of 16x16 pixels
66	// Each block in transmitted in turn, line-by-line.
67	for (y = 0; y < h; y += 16) {
68		for (x = 0; x < w; x += 16) {
69		for (i = 0; i < 16; i++) {
70			memcpy(dst + x + (y + i) * dstride, src, 16);
71			src += 16;
72		}
73		}
74	}
75	}
76
77	static void de_macro_uv(unsigned char *dstu, unsigned char *dstv, unsigned char *src, int dstride, int w, int h)
78	{
79	unsigned int y, x, i;
80
81	// descramble U/V plane
82	// dstride = 720 / 2 = w
83	// The U/V values are interlaced (UVUV...).
84	// Again, the UV plane is divided into blocks of 16x16 UV values.
85	// Each block in transmitted in turn, line-by-line.
86	for (y = 0; y < h; y += 16) {
87		for (x = 0; x < w; x += 8) {
88		for (i = 0; i < 16; i++) {
89			int idx = x + (y + i) * dstride;
90
91			dstu[idx+0] = src[0];  dstv[idx+0] = src[1];
92			dstu[idx+1] = src[2];  dstv[idx+1] = src[3];
93			dstu[idx+2] = src[4];  dstv[idx+2] = src[5];
94			dstu[idx+3] = src[6];  dstv[idx+3] = src[7];
95			dstu[idx+4] = src[8];  dstv[idx+4] = src[9];
96			dstu[idx+5] = src[10]; dstv[idx+5] = src[11];
97			dstu[idx+6] = src[12]; dstv[idx+6] = src[13];
98			dstu[idx+7] = src[14]; dstv[idx+7] = src[15];
99			src += 16;
100		}
101		}
102	}
103	}
104
105	/*************************************************************************/
106	int main(int argc, char **argv)
107	{
108	FILE *fin;
109	int i;
110
111	if (argc == 1) fin = stdin;
112	else fin = fopen(argv[1], "r");
113
114	if (fin == NULL) {
115		fprintf(stderr, "cannot open input\n");
116		exit(-1);
117	}
118	while (fread(frame, sizeof(frame), 1, fin) == 1) {
119		de_macro_y(framey, frame, 720, 720, 576);
120		de_macro_uv(frameu, framev, frame + 720 * 576, 720 / 2, 720 / 2, 576 / 2);
121		fwrite(framey, sizeof(framey), 1, stdout);
122		fwrite(framev, sizeof(framev), 1, stdout);
123		fwrite(frameu, sizeof(frameu), 1, stdout);
124	}
125	fclose(fin);
126	return 0;
127	}
128
129
130Format of embedded V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data
131---------------------------------------------------------
132
133Author: Hans Verkuil <hverkuil@xs4all.nl>
134
135
136This section describes the V4L2_MPEG_STREAM_VBI_FMT_IVTV format of the VBI data
137embedded in an MPEG-2 program stream. This format is in part dictated by some
138hardware limitations of the ivtv driver (the driver for the Conexant cx23415/6
139chips), in particular a maximum size for the VBI data. Anything longer is cut
140off when the MPEG stream is played back through the cx23415.
141
142The advantage of this format is it is very compact and that all VBI data for
143all lines can be stored while still fitting within the maximum allowed size.
144
145The stream ID of the VBI data is 0xBD. The maximum size of the embedded data is
1464 + 43 * 36, which is 4 bytes for a header and 2 * 18 VBI lines with a 1 byte
147header and a 42 bytes payload each. Anything beyond this limit is cut off by
148the cx23415/6 firmware. Besides the data for the VBI lines we also need 36 bits
149for a bitmask determining which lines are captured and 4 bytes for a magic cookie,
150signifying that this data package contains V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data.
151If all lines are used, then there is no longer room for the bitmask. To solve this
152two different magic numbers were introduced:
153
154'itv0': After this magic number two unsigned longs follow. Bits 0-17 of the first
155unsigned long denote which lines of the first field are captured. Bits 18-31 of
156the first unsigned long and bits 0-3 of the second unsigned long are used for the
157second field.
158
159'ITV0': This magic number assumes all VBI lines are captured, i.e. it implicitly
160implies that the bitmasks are 0xffffffff and 0xf.
161
162After these magic cookies (and the 8 byte bitmask in case of cookie 'itv0') the
163captured VBI lines start:
164
165For each line the least significant 4 bits of the first byte contain the data type.
166Possible values are shown in the table below. The payload is in the following 42
167bytes.
168
169Here is the list of possible data types:
170
171.. code-block:: c
172
173	#define IVTV_SLICED_TYPE_TELETEXT       0x1     // Teletext (uses lines 6-22 for PAL)
174	#define IVTV_SLICED_TYPE_CC             0x4     // Closed Captions (line 21 NTSC)
175	#define IVTV_SLICED_TYPE_WSS            0x5     // Wide Screen Signal (line 23 PAL)
176	#define IVTV_SLICED_TYPE_VPS            0x7     // Video Programming System (PAL) (line 16)
177
178