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| 06:26 | se6ast1an | good day
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| 19:46 | anuejn | Bertl_oO: why is the fill order of the current raw12 files the way it is
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| 19:46 | anuejn | it seems... not very handy
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| 20:47 | Bertl_oO | you mean the RG/GB/O pattern?
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| 20:51 | anuejn | no
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| 20:51 | anuejn | intuitively I would expect the data to be packed this way:
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| 20:52 | anuejn | (assuming the least significant bit is written right and the byte with the lowest address is the rightmost byte)
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| 20:52 | anuejn | BA987654 3210BA98 76543210
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| 20:53 | anuejn | but the data is encoded this way:
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| 20:53 | Bertl_oO | i.e. little endian?
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| 20:53 | anuejn | yes somehow something like that but it is not clear to me how le and be interact with the data being 12 bit
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| 20:54 | anuejn | 76543210 3210BA98 BA987654
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| 20:55 | Bertl_oO | how do you look at the data? i.e. who assembles the bytes here?
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| 20:55 | Bertl_oO | and is that system little or big endian :)
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| 20:55 | anuejn | err 76543210 BA983210 BA987654
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| 20:56 | anuejn | currently I am doing this more or less in my head
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| 20:56 | Bertl_oO | well, if you have the following bytes:
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| 20:56 | Bertl_oO | 01 23 45 67 89 (all hex)
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| 20:56 | anuejn | but afaik all the systems I work with are little endian (x86 and arm)
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| 20:57 | Bertl_oO | then there is one way to create a 'stream' of bytes from left to right
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| 20:57 | Bertl_oO | 0123456789....
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| 20:57 | Bertl_oO | now if you cut that into 12bit sequences, the question is what bit comes first
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| 20:58 | Bertl_oO | i.e. big endian, you start with 102
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| 20:58 | anuejn | is your lowest memory addres on the right or on the left?
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| 20:58 | Bertl_oO | lowest memory is the first byte
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| 20:58 | Bertl_oO | i.e. on the left
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| 20:58 | anuejn | okay
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| 20:59 | Bertl_oO | ah, sorry, big endian would be 103
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| 20:59 | Bertl_oO | and little endian will be 012
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| 21:00 | Bertl_oO | it is basically one of those two options if you consider byte streams
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| 21:00 | Bertl_oO | now the real problem comes when you read the bytes in larger chunks
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| 21:01 | Bertl_oO | e.g. read 4 bytes in one 32bit word
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| 21:01 | Bertl_oO | because now the bytes can get read in two different orders depending on the endianess
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| 21:02 | Bertl_oO | so 01 23 45 67 might end up as 01234567 or 67452301
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| 21:02 | anuejn | I see that
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| 21:03 | anuejn | so your gateware writes the 12bit values big endian packed?
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| 21:04 | Bertl_oO | the data is packed in the natural order (FPGA) side and then written out by the AXI interface (without any reordering)
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| 21:04 | Bertl_oO | the arm architecture is by default big endian, although it can do little endian as well
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| 21:05 | anuejn | arm is big endian o_O?
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| 21:06 | anuejn | hm... my original confusion comes from the fact that I am also packing the data in the natural order from the fpga and write it to the axi interface
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| 21:06 | BAndiT1983 | wiki says the opposite is the case
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| 21:06 | BAndiT1983 | little-endianness is the dominant ordering for processor architectures (x86, most ARM implementations, base RISC-V implementations) and their associated memory.
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| 21:06 | anuejn | then I stream it over ethernet and I get different data than you
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| 21:08 | Bertl_oO | sorry, the other way round, little endian and can do big endian
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| 21:08 | anuejn | okay
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| 21:08 | anuejn | so everything in the process is le
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| 21:09 | anuejn | and I guess the natural order in the fpga is also le
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| 21:12 | Bertl_oO | no idea, IIRC, AXI is considered endianess invariant
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| 21:13 | anuejn | hm... I guess I have to read your gearbox then
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| 21:14 | Bertl_oO | the main question is if the difference doesn't come from the userspace tools repacking the image
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| 21:15 | Bertl_oO | i.e. are you looking at the .raw files or are you looking at the frame buffer memory in the beta
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| 21:15 | anuejn | I am loading the .raw12 files
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| 21:15 | Bertl_oO | because we changed the .raw format so often, that I do not have a clue what we currently do there anymore :)
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| 21:15 | anuejn | ah I see that
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| 21:16 | anuejn | I am quite confued myself (as you might see)
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| 21:16 | Bertl_oO | it is definitely confusing :)
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| 21:16 | anuejn | somehow dng only seems to allow your packing and not mine
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| 21:17 | anuejn | > If BitsPerSample is not equal to 8 or 16 or 32, then the bits
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| 21:17 | anuejn | must be packed into bytes using the TIFF default FillOrder of 1 (big-endian), even if the TIFF
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| 21:17 | anuejn | file itself uses little-endian byte order.
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| 21:18 | Bertl_oO | IIRC, we changed something back then to make dng happy, but I'm not sure if that was in the format or not
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| 21:18 | anuejn | that seems... dumb to me
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| 21:18 | anuejn | ah probably it was
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| 21:18 | anuejn | that explains that
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| 21:18 | Bertl_oO | alexML probably knows more there
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| 21:18 | anuejn | so cmv_snap already does a lot of that byte cooking?
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| 21:19 | Bertl_oO | I think DNG is somehow related to TIFF and if I'm not mistaken, TIFF is big endian encoded
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| 21:19 | BAndiT1983 | DNG is TIFF extension
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| 21:20 | BAndiT1983 | TIFF has also the endianess marker at the beginning
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| 21:20 | anuejn | TIFF can do both ;)
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| 21:20 | BAndiT1983 | II or MM
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| 21:20 | anuejn | but the quote that I posted forbids the use of le bit packing
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| 21:20 | BAndiT1983 | Every TIFF file begins with a two-byte indicator of byte order: "II" for little-endian (a.k.a. "Intel byte ordering", circa 1980)[9] or "MM" for big-endian (a.k.a. "Motorola byte ordering", circa 1980)[9] byte ordering.
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| 21:20 | BAndiT1983 | https://en.wikipedia.org/wiki/TIFF
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| 21:21 | Bertl_oO | we can agree that it is all very confusing :)
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| 21:22 | BAndiT1983 | is the packing in TIFF really always LE?
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| 21:25 | anuejn | no but in 12bit dng
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| 21:25 | anuejn | Bertl_oO: +1
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| 21:31 | anuejn | has an exploded head
| | 21:32 | BAndiT1983 | https://thumbs.gfycat.com/BiodegradableVelvetyAnglerfish-mobile.mp4
|