Circbuf - Revision history

Andrey.filippov: /* Circbuf data access - /dev/circbuf */

2007-12-01T07:26:46Z

Circbuf data access - /dev/circbuf

← Older revision		Revision as of 07:26, 1 December 2007
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	*'''CIRCLSEEK_READY''' - verify the frame at current location is available (valid and acquired) Returns file pointer if ready, else - an error. If the file pointer was set to FPGA write pointer it will pass validation with CIRCLSEEK_VALID ( the pointer is still valid and not overrun by the later data), but will fail CIRCLSEEK_READY (frame is not ready), for all other pointers CIRCLSEEK_VALID and CIRCLSEEK_READY will give the identical result.		*'''CIRCLSEEK_READY''' - verify the frame at current location is available (valid and acquired) Returns file pointer if ready, else - an error. If the file pointer was set to FPGA write pointer it will pass validation with CIRCLSEEK_VALID ( the pointer is still valid and not overrun by the later data), but will fail CIRCLSEEK_READY (frame is not ready), for all other pointers CIRCLSEEK_VALID and CIRCLSEEK_READY will give the identical result.
	*'''CIRCLSEEK_WAIT''' - this call will put the process to sleep until the image will be available at the current pointer. The actual sleep will take place only if the current pointer is equal to FPGA write pointer, in all other cases it will return immediately. If the pointer was invalid (i.e. overrun) the call will return with an error as there is no sense to wait for a frame here. If the pointer is valid but is not equal to write pointer - frame is already available and the call will return with current pointer immediately.		*'''CIRCLSEEK_WAIT''' - this call will put the process to sleep until the image will be available at the current pointer. The actual sleep will take place only if the current pointer is equal to FPGA write pointer, in all other cases it will return immediately. If the pointer was invalid (i.e. overrun) the call will return with an error as there is no sense to wait for a frame here. If the pointer is valid but is not equal to write pointer - frame is already available and the call will return with current pointer immediately.
	*'''CIRCLSEEK_FREE''' - returnes remaining memory in circbuf from the current file pointer, or -EINVAL if the pointer is invalid. As this command uses the buffer write pointer that is updated only when the complete frame is in the buffer, the actual free memory may be less by a whole frame if compressor is running.		*'''CIRCLSEEK_FREE''' - returnes remaining memory in circbuf from the current file pointer, or -EINVAL if the pointer is invalid. As this command uses the buffer write pointer that is updated only when the complete frame is in the buffer, the actual free memory may be less by a whole frame if compressor is running. ''' Has a side effect of moving file pointer - should be saved/restored'''
	*'''CIRCLSEEK_USED ''' - returnes memory used in the in circbuf from the current file pointer, or -EINVAL if the pointer is invalid		*'''CIRCLSEEK_USED ''' - returnes memory used in the in circbuf from the current file pointer, or -EINVAL if the pointer is invalid. ''' Has a side effect of moving file pointer - should be saved/restored'''

	==Reading JPEG headers==		==Reading JPEG headers==

Andrey.filippov: /* Circbuf data access - /dev/circbuf */

2007-11-16T10:03:03Z

Circbuf data access - /dev/circbuf

← Older revision		Revision as of 10:03, 16 November 2007
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	*'''CIRCLSEEK_READY''' - verify the frame at current location is available (valid and acquired) Returns file pointer if ready, else - an error. If the file pointer was set to FPGA write pointer it will pass validation with CIRCLSEEK_VALID ( the pointer is still valid and not overrun by the later data), but will fail CIRCLSEEK_READY (frame is not ready), for all other pointers CIRCLSEEK_VALID and CIRCLSEEK_READY will give the identical result.		*'''CIRCLSEEK_READY''' - verify the frame at current location is available (valid and acquired) Returns file pointer if ready, else - an error. If the file pointer was set to FPGA write pointer it will pass validation with CIRCLSEEK_VALID ( the pointer is still valid and not overrun by the later data), but will fail CIRCLSEEK_READY (frame is not ready), for all other pointers CIRCLSEEK_VALID and CIRCLSEEK_READY will give the identical result.
	*'''CIRCLSEEK_WAIT''' - this call will put the process to sleep until the image will be available at the current pointer. The actual sleep will take place only if the current pointer is equal to FPGA write pointer, in all other cases it will return immediately. If the pointer was invalid (i.e. overrun) the call will return with an error as there is no sense to wait for a frame here. If the pointer is valid but is not equal to write pointer - frame is already available and the call will return with current pointer immediately.		*'''CIRCLSEEK_WAIT''' - this call will put the process to sleep until the image will be available at the current pointer. The actual sleep will take place only if the current pointer is equal to FPGA write pointer, in all other cases it will return immediately. If the pointer was invalid (i.e. overrun) the call will return with an error as there is no sense to wait for a frame here. If the pointer is valid but is not equal to write pointer - frame is already available and the call will return with current pointer immediately.
			*'''CIRCLSEEK_FREE''' - returnes remaining memory in circbuf from the current file pointer, or -EINVAL if the pointer is invalid. As this command uses the buffer write pointer that is updated only when the complete frame is in the buffer, the actual free memory may be less by a whole frame if compressor is running.
			*'''CIRCLSEEK_USED ''' - returnes memory used in the in circbuf from the current file pointer, or -EINVAL if the pointer is invalid

	==Reading JPEG headers==		==Reading JPEG headers==

Andrey.filippov at 07:04, 11 October 2007

2007-10-11T07:04:26Z

Andrey.filippov: /* Circbuf data access - /dev/circbuf */

2007-10-06T17:49:36Z

Circbuf data access - /dev/circbuf

← Older revision		Revision as of 17:49, 6 October 2007
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	*'''CIRCLSEEK_VALID''' - verify that the frame at the current location is valid (not overrun in the buffer) Returns file pointer if valid, else - an error.		*'''CIRCLSEEK_VALID''' - verify that the frame at the current location is valid (not overrun in the buffer) Returns file pointer if valid, else - an error.
	*'''CIRCLSEEK_READY''' - verify the frame at current location is available (valid and acquired) Returns file pointer if ready, else - an error. If the file pointer was set to FPGA write pointer it will pass validation with CIRCLSEEK_VALID ( the pointer is still valid and not overrun by the later data), but will fail CIRCLSEEK_READY (frame is not ready), for all other pointers CIRCLSEEK_VALID and CIRCLSEEK_READY will give the identical result.		*'''CIRCLSEEK_READY''' - verify the frame at current location is available (valid and acquired) Returns file pointer if ready, else - an error. If the file pointer was set to FPGA write pointer it will pass validation with CIRCLSEEK_VALID ( the pointer is still valid and not overrun by the later data), but will fail CIRCLSEEK_READY (frame is not ready), for all other pointers CIRCLSEEK_VALID and CIRCLSEEK_READY will give the identical result.
	*'''CIRCLSEEK_WAIT''' - this call will put the process to ~~slip~~ until the image will be available at the current pointer. The actual sleep will take place only if the current pointer is equal to FPGA write pointer, in all other cases it will return immediately. If the pointer was invalid (i.e. overrun) the call will return with an error as there is no sense to wait for a frame here. If the pointer is valid but is not equal to write pointer - frame is already available and the call will return with current pointer immediately.		*'''CIRCLSEEK_WAIT''' - this call will put the process to sleep until the image will be available at the current pointer. The actual sleep will take place only if the current pointer is equal to FPGA write pointer, in all other cases it will return immediately. If the pointer was invalid (i.e. overrun) the call will return with an error as there is no sense to wait for a frame here. If the pointer is valid but is not equal to write pointer - frame is already available and the call will return with current pointer immediately.

	==Reading JPEG headers==		==Reading JPEG headers==

Andrey.filippov: /* Circbuf data access - /dev/circbuf */

2007-10-06T17:48:28Z

Circbuf data access - /dev/circbuf

← Older revision		Revision as of 17:48, 6 October 2007
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	*'''CIRCLSEEK_FIRST''' - move pointer to the oldest acquired frame that still is available in the buffer. It is OK to browse through the frames in the buffer including that one when the image acquisition is stopped, but it is not safe to rely on this pointer if more frames are expected - next incoming frame can overwrite this one.		*'''CIRCLSEEK_FIRST''' - move pointer to the oldest acquired frame that still is available in the buffer. It is OK to browse through the frames in the buffer including that one when the image acquisition is stopped, but it is not safe to rely on this pointer if more frames are expected - next incoming frame can overwrite this one.
	*'''CIRCLSEEK_SCND''' - move pointer to the second oldest acquired frame. A slightly safer to use instead of CIRCLSEEK_FIRST when constant acquisition is on and sensor provides new frames - this frame will likely survive longer and give you a chance for the CIRCLSEEK_NEXT at least to buy some more time.		*'''CIRCLSEEK_SCND''' - move pointer to the second oldest acquired frame. A slightly safer to use instead of CIRCLSEEK_FIRST when constant acquisition is on and sensor provides new frames - this frame will likely survive longer and give you a chance for the CIRCLSEEK_NEXT at least to buy some more time.
	*'''CIRCLSEEK_SETP''' - save current pointer to global read pointer. This will allow to continue from the same frame next time the circbuf will be accessed as the global read pointer survives closing the circbuf file. But it is a global variable, so if several clients use this pointer they might interfere with each other.		*'''CIRCLSEEK_SETP''' - save current pointer to the global read pointer. This will allow to continue from the same frame next time the circbuf will be accessed as the global read pointer survives closing the circbuf file. But it is a global variable, so if several clients use this pointer they might interfere with each other.
	*'''CIRCLSEEK_VALID''' - verify that the frame at the current location is valid (not overrun in the buffer) Returns file pointer if valid, else - an error.		*'''CIRCLSEEK_VALID''' - verify that the frame at the current location is valid (not overrun in the buffer) Returns file pointer if valid, else - an error.
	*'''CIRCLSEEK_READY''' - verify the frame at current location is available (valid and acquired) Returns file pointer if ready, else - an error. If the file pointer was set to FPGA write pointer it will pass validation with CIRCLSEEK_VALID ( the pointer is still valid and not overrun by the later data), but will fail CIRCLSEEK_READY (frame is not ready), for all other pointers CIRCLSEEK_VALID and CIRCLSEEK_READY will give the identical result.		*'''CIRCLSEEK_READY''' - verify the frame at current location is available (valid and acquired) Returns file pointer if ready, else - an error. If the file pointer was set to FPGA write pointer it will pass validation with CIRCLSEEK_VALID ( the pointer is still valid and not overrun by the later data), but will fail CIRCLSEEK_READY (frame is not ready), for all other pointers CIRCLSEEK_VALID and CIRCLSEEK_READY will give the identical result.

Andrey.filippov: /* Circbuf data access - /dev/circbuf */

2007-10-06T17:45:26Z

Circbuf data access - /dev/circbuf

← Older revision		Revision as of 17:45, 6 October 2007
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	"Current pointer" or "selected frame" in the description below references to the file pointer of an opened file. As soon as the /dev/circbuf file is closed (usually happens between individual accesses through the web server), the value of such pointer is lost.		"Current pointer" or "selected frame" in the description below references to the file pointer of an opened file. As soon as the /dev/circbuf file is closed (usually happens between individual accesses through the web server), the value of such pointer is lost.

	*'''CIRCLSEEK_TORP''' .- set file pointer to global (shared) read pointer. This pointer is maintained by the camera driver and preserves the value even when particular file access to circbuf is closed, it is valid for individual accesses to the camera through embedded web servers. But this pointer is the shared one, so it will have predictable values only if there is a single client to manipulate it.		*'''CIRCLSEEK_TORP''' - set file pointer to global (shared) read pointer. This pointer is maintained by the camera driver and preserves the value even when particular file access to circbuf is closed, it is valid for individual accesses to the camera through embedded web servers. But this pointer is the shared one, so it will have predictable values only if there is a single client to manipulate it.
	*'''CIRCLSEEK_TOWP''' - set file pointer to FPGA write pointer. This is the "hardware" pointer in the circbuf (next frame to be acquired). There is no frame available at that position in the circbuf, but it is a good place to wait for the next frame to come.		*'''CIRCLSEEK_TOWP''' - set file pointer to FPGA write pointer. This is the "hardware" pointer in the circbuf (next frame to be acquired). There is no frame available at that position in the circbuf, but it is a good place to wait for the next frame to come.
	*'''CIRCLSEEK_PREV''' - move frame pointer to the previous one (acquired just before the currently selected), the call will return an negative number -- error (-EOVERFLOW) if there are none frames in the buffer older than the currently pointed one. That can be the case if there are not enough frames acquired since last circbuf buffer reset or if the newer frames had overwritten the ones before the current.		*'''CIRCLSEEK_PREV''' - move frame pointer to the previous one (acquired just before the currently selected), the call will return an negative number -- error (-EOVERFLOW) if there are none frames in the buffer older than the currently pointed one. That can be the case if there are not enough frames acquired since last circbuf buffer reset or if the newer frames had overwritten the ones before the current.

Andrey.filippov: /* Circbuf data access - /dev/circbuf */

2007-10-06T17:42:56Z

Circbuf data access - /dev/circbuf

← Older revision		Revision as of 17:42, 6 October 2007
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	Normally lseek (also fseek, ftell) are designed to move file pointer and find out current pointer position. For example these functions can be used to determine the file size - move the file pointer to the end of file at read it value back. The last argument of lseek (fseek) function (called ''whence'' for some historical reasons) can take one of the 3 values:		Normally lseek (also fseek, ftell) are designed to move file pointer and find out current pointer position. For example these functions can be used to determine the file size - move the file pointer to the end of file at read it value back. The last argument of lseek (fseek) function (called ''whence'' for some historical reasons) can take one of the 3 values:
	*'''SEEK_SET''' - passed offset value (2-nd argument) used directly as the new pointer position (i.e. ~~fssek~~(''file'',0,SEEK_SET) would place the pointer at the very beginning of the file)		*'''SEEK_SET''' - passed offset value (2-nd argument) used directly as the new pointer position (i.e. fseek(''file'',0,SEEK_SET) would place the pointer at the very beginning of the file)
	*'''SEEK_CUR''' - relative movement of the file pointer. lseek(''fp'',0,SEEK_CUR) will return current position without modifying it (like ftell(''file''))		*'''SEEK_CUR''' - relative movement of the file pointer. lseek(''fp'',0,SEEK_CUR) will return current position without modifying it (like ftell(''file''))
	*'''SEEK_END''' - move file pointer relative to the end of file, so any positive value of offset moves file pointer beyond the end of file. It is not considered to be an error - normal files can be written to beyond the current file length. This is not applicable to current implementation of the circbuf (it has a fixed size), so the SEEK_END with positive (>0) values of offset are used to perform several specific actions with the pointers to circbuf data and to wait for the next image to be acquired. Using SEEK_END with offset==0 (or negative) will have no difference to normal implementations, fseek(''file'', 0, SEEK_END) will move the file pointer just after the last byte in the circbuf. All the accesses with SEEK_CUR, SEEK_SET will use the fact that the buffer is circular - the file pointer will just roll over, so fseek (''file'', -2, SEEK_SET) will position the pointer just in front of the 2 last bytes of the circbuf.		*'''SEEK_END''' - move file pointer relative to the end of file, so any positive value of offset moves file pointer beyond the end of file. It is not considered to be an error - normal files can be written to beyond the current file length. This is not applicable to current implementation of the circbuf (it has a fixed size), so the SEEK_END with positive (>0) values of offset are used to perform several specific actions with the pointers to circbuf data and to wait for the next image to be acquired. Using SEEK_END with offset==0 (or negative) will have no difference to normal implementations, fseek(''file'', 0, SEEK_END) will move the file pointer just after the last byte in the circbuf. All the accesses with SEEK_CUR, SEEK_SET will use the fact that the buffer is circular - the file pointer will just roll over, so fseek (''file'', -2, SEEK_SET) will position the pointer just in front of the 2 last bytes of the circbuf.

Andrey.filippov: /* Circbuf data access - /dev/circbuf */

2007-10-06T17:42:18Z

Circbuf data access - /dev/circbuf

← Older revision		Revision as of 17:42, 6 October 2007
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	=== Circbuf data access - /dev/circbuf ===		=== Circbuf data access - /dev/circbuf ===

	User access to the circular buffer is provided by the /dev/circbuf device driver. It is now in [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/arch/cris/arch-v32/drivers/elphel/circbuf.c arch/cris/arch-v32/drivers/elphel/circbuf.c]. That device supports read, write, poll methods, but the most important are '''mmap''' and '''(overloaded) lseek'''. mmap provides direct access to the circbuf data, lseek is overloaded to include additional functions that are normally implemented in ioctl. It is a hack, of course, but gives easy access to the buffer data (and meta ~~ata~~) from the PHP scripts.		User access to the circular buffer is provided by the /dev/circbuf device driver. It is now in [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/arch/cris/arch-v32/drivers/elphel/circbuf.c arch/cris/arch-v32/drivers/elphel/circbuf.c]. That device supports read, write, poll methods, but the most important are '''mmap''' and '''(overloaded) lseek'''. mmap provides direct access to the circbuf data, lseek is overloaded to include additional functions that are normally implemented in ioctl. It is a hack, of course, but gives easy access to the buffer data (and meta data) from the PHP scripts.

	Normally lseek (also fseek, ftell) are designed to move file pointer and find out current pointer position. For example these functions can be used to determine the file size - move the file pointer to the end of file at read it value back. The last argument of lseek (fseek) function (called ''whence'' for some historical reasons) can take one of the 3 values:		Normally lseek (also fseek, ftell) are designed to move file pointer and find out current pointer position. For example these functions can be used to determine the file size - move the file pointer to the end of file at read it value back. The last argument of lseek (fseek) function (called ''whence'' for some historical reasons) can take one of the 3 values:

Andrey.filippov: /* Circbuf data access - /dev/circbuf */

2007-10-06T17:41:53Z

Circbuf data access - /dev/circbuf

← Older revision		Revision as of 17:41, 6 October 2007
Line 84:		Line 84:
	=== Circbuf data access - /dev/circbuf ===		=== Circbuf data access - /dev/circbuf ===

	User access to the circular buffer is provided by the /dev/circbuf device driver. It is now in [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/arch/cris/arch-v32/drivers/elphel/circbuf.c arch/cris/arch-v32/drivers/elphel/circbuf.c]. That device supports read, write, poll methods, but the most important are '''mmap''' and '''(overloaded) lseek'''. mmap provides direct access to the circbuf data, lseek is overloaded to include additional functions that normally implemented in ioctl. It is a hack, of course, but gives easy access to the buffer data (and meta ata) from the PHP scripts.		User access to the circular buffer is provided by the /dev/circbuf device driver. It is now in [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/arch/cris/arch-v32/drivers/elphel/circbuf.c arch/cris/arch-v32/drivers/elphel/circbuf.c]. That device supports read, write, poll methods, but the most important are '''mmap''' and '''(overloaded) lseek'''. mmap provides direct access to the circbuf data, lseek is overloaded to include additional functions that are normally implemented in ioctl. It is a hack, of course, but gives easy access to the buffer data (and meta ata) from the PHP scripts.

	Normally lseek (also fseek, ftell) are designed to move file pointer and find out current pointer position. For example these functions can be used to determine the file size - move the file pointer to the end of file at read it value back. The last argument of lseek (fseek) function (called ''whence'' for some historical reasons) can take one of the 3 values:		Normally lseek (also fseek, ftell) are designed to move file pointer and find out current pointer position. For example these functions can be used to determine the file size - move the file pointer to the end of file at read it value back. The last argument of lseek (fseek) function (called ''whence'' for some historical reasons) can take one of the 3 values:

Andrey.filippov: /* Frame metadata stored in the circbuf (added by the software) */

2007-10-06T17:38:48Z

Frame metadata stored in the circbuf (added by the software)

← Older revision		Revision as of 17:38, 6 October 2007
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	*updating software pointer (JPEG_wp) after each new frame is compressed to match the location where next frame bitstream will be output,		*updating software pointer (JPEG_wp) after each new frame is compressed to match the location where next frame bitstream will be output,
	*copying the bitstream length before the frame itself (no simplify traversing frames) - it is now at 0x4b7fff (copied from 0xde4f lower 24 bits)		*copying the bitstream length before the frame itself (no simplify traversing frames) - it is now at 0x4b7fff (copied from 0xde4f lower 24 bits)
	*writing 2 of the 0xff bytes just before the length as a marker of valid frame header (incoming compressed bitstream data will never have ~~2 0xffs~~, and the microsecond high byte, that might be written at that location is always 0)		*writing 2 of the 0xff bytes just before the length as a marker of valid frame header (incoming compressed bitstream data will never have two of 0xff bytes together, and the microsecond high byte, that might be written at that location is always 0)
	*filling in the 26 byte remaining area right before the last frame acquired - it is now safe until the whole buffer will be filled with image data. In the example above it starts at 0x4b7ff8.		*filling in the 26 byte remaining area right before the last frame acquired - it is now safe until the whole buffer will be filled with image data. In the example above it starts at 0x4b7ff8.

← Older revision		Revision as of 07:04, 11 October 2007
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	=== Circular buffer in Elphel 353 camera ===		=== Circular buffer in Elphel 353 camera ===

	The compressed frames are stored in the large circular buffer, it is done similar in the previous cameras and with other compressor (Ogg Theora) but the following description applies to the current state of the firmware (7.1.0.1) of the model 353 camera with JPEG compressor (Theora branch is not ported yet as of September 2007). Currently buffer size - CCAM_DMA_SIZE is ~19MB as defined in [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/include/asm-cris/elphel/c313a.h?view=markup include/asm-cris/elphel/c313a.h]).		The compressed frames are stored in the large circular buffer, it is done similar in the previous cameras and with other compressor (Ogg Theora) but the following description applies to the current state of the firmware (7.1.0.1) of the model 353 camera with JPEG compressor (Theora branch is not ported yet as of September 2007). Currently buffer size - CCAM_DMA_SIZE is ~19MB as defined in [http://elphel.cvs.sourceforge.net/elphel/elphel353-7.1/os/linux-2.6-tag--devboard-R2_10-4/include/asm-cris/elphel/c313a.h?view=markup include/asm-cris/elphel/c313a.h]).

	All DMA transfers are 32-bytes aligned (32 bytes is a size of the internal DMA buffer in Etrax), and the data received from the FPGA contains JPEG-encode bit stream -- everything between SOF and EOF tags, no header, all 0xff data bytes escaped by appropriate 0x00 codes as required by the standard, so no 2 0xff bytes can appear together - this fact is used to find out if the data in the circular buffer was overwritten by the newer image frames.		All DMA transfers are 32-bytes aligned (32 bytes is a size of the internal DMA buffer in Etrax), and the data received from the FPGA contains JPEG-encode bit stream -- everything between SOF and EOF tags, no header, all 0xff data bytes escaped by appropriate 0x00 codes as required by the standard, so no 2 0xff bytes can appear together - this fact is used to find out if the data in the circular buffer was overwritten by the newer image frames.
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	When FPGA outputs the whole frame (it does not know the frame size in advance, only after compression is over) it adds 12 more bytes (3 long words), aligning them to the end of the 32-byte chunk, adding zeros before the data if needed. The last 4 bytes contain a 24-bit byte length of the JPEG data with the high byte set to 0xff. 8 bytes before (2 long words) have timestamp of the frame exposure start - seconds from epoch and microseconds.		When FPGA outputs the whole frame (it does not know the frame size in advance, only after compression is over) it adds 12 more bytes (3 long words), aligning them to the end of the 32-byte chunk, adding zeros before the data if needed. The last 4 bytes contain a 24-bit byte length of the JPEG data with the high byte set to 0xff. 8 bytes before (2 long words) have timestamp of the frame exposure start - seconds from epoch and microseconds.

	The following listing has a sample of the buffer data (generated by the [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/apps/test_mmap/test_mmap.c?view=markup /usr/local/bin/test_mmap]):		The following listing has a sample of the buffer data (generated by the [http://elphel.cvs.sourceforge.net/elphel/elphel353-7.1/apps/test_mmap/test_mmap.c?view=markup /usr/local/bin/test_mmap]):

	4b7ff8: 000000a4 06000800 016c0120 0a3946c1 01ab010a 40404040 ffff0000 000378fe		4b7ff8: 000000a4 06000800 016c0120 0a3946c1 01ab010a 40404040 ffff0000 000378fe
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	=== Frame metadata stored in the circbuf (added by the software) ===		=== Frame metadata stored in the circbuf (added by the software) ===

	The interrupt service routine [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/arch/cris/arch-v32/drivers/elphel/cc353.c?view=markup arch/cris/arch-v32/drivers/elphel/cc353.c::camSeq_interrupt] is responsible for		The interrupt service routine [http://elphel.cvs.sourceforge.net/elphel/elphel353-7.1/os/linux-2.6-tag--devboard-R2_10-4/arch/cris/arch-v32/drivers/elphel/cc353.c?view=markup arch/cris/arch-v32/drivers/elphel/cc353.c::camSeq_interrupt] is responsible for
	*updating software pointer (JPEG_wp) after each new frame is compressed to match the location where next frame bitstream will be output,		*updating software pointer (JPEG_wp) after each new frame is compressed to match the location where next frame bitstream will be output,
	*copying the bitstream length before the frame itself (no simplify traversing frames) - it is now at 0x4b7fff (copied from 0xde4f lower 24 bits)		*copying the bitstream length before the frame itself (no simplify traversing frames) - it is now at 0x4b7fff (copied from 0xde4f lower 24 bits)
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	*filling in the 26 byte remaining area right before the last frame acquired - it is now safe until the whole buffer will be filled with image data. In the example above it starts at 0x4b7ff8.		*filling in the 26 byte remaining area right before the last frame acquired - it is now safe until the whole buffer will be filled with image data. In the example above it starts at 0x4b7ff8.

	The 26 (actually 28, as 0xffff marker is also included in the memcpy) bytes are copied from the data structure ''frame_params_t'' defined in [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/include/asm-cris/elphel/c313a.h?view=markup include/asm-cris/elphel/c313a.h]		The 26 (actually 28, as 0xffff marker is also included in the memcpy) bytes are copied from the data structure ''frame_params_t'' defined in [http://elphel.cvs.sourceforge.net/elphel/elphel353-7.1/os/linux-2.6-tag--devboard-R2_10-4/include/asm-cris/elphel/c313a.h?view=markup include/asm-cris/elphel/c313a.h]
	struct frame_params_t {		struct frame_params_t {
	/00-03/ unsigned long exposure; //! currently - exposure time measured in 100usec. Really need to change it to smaller increments?		/00-03/ unsigned long exposure; //! currently - exposure time measured in 100usec. Really need to change it to smaller increments?
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	=== Circbuf data access - /dev/circbuf ===		=== Circbuf data access - /dev/circbuf ===

	User access to the circular buffer is provided by the /dev/circbuf device driver. It is now in [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/arch/cris/arch-v32/drivers/elphel/circbuf.c arch/cris/arch-v32/drivers/elphel/circbuf.c]. That device supports read, write, poll methods, but the most important are '''mmap''' and '''(overloaded) lseek'''. mmap provides direct access to the circbuf data, lseek is overloaded to include additional functions that are normally implemented in ioctl. It is a hack, of course, but gives easy access to the buffer data (and meta data) from the PHP scripts.		User access to the circular buffer is provided by the /dev/circbuf device driver. It is now in [http://elphel.cvs.sourceforge.net/elphel/elphel353-7.1/os/linux-2.6-tag--devboard-R2_10-4/arch/cris/arch-v32/drivers/elphel/circbuf.c arch/cris/arch-v32/drivers/elphel/circbuf.c]. That device supports read, write, poll methods, but the most important are '''mmap''' and '''(overloaded) lseek'''. mmap provides direct access to the circbuf data, lseek is overloaded to include additional functions that are normally implemented in ioctl. It is a hack, of course, but gives easy access to the buffer data (and meta data) from the PHP scripts.

	Normally lseek (also fseek, ftell) are designed to move file pointer and find out current pointer position. For example these functions can be used to determine the file size - move the file pointer to the end of file at read it value back. The last argument of lseek (fseek) function (called ''whence'' for some historical reasons) can take one of the 3 values:		Normally lseek (also fseek, ftell) are designed to move file pointer and find out current pointer position. For example these functions can be used to determine the file size - move the file pointer to the end of file at read it value back. The last argument of lseek (fseek) function (called ''whence'' for some historical reasons) can take one of the 3 values:
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	*'''SEEK_END''' - move file pointer relative to the end of file, so any positive value of offset moves file pointer beyond the end of file. It is not considered to be an error - normal files can be written to beyond the current file length. This is not applicable to current implementation of the circbuf (it has a fixed size), so the SEEK_END with positive (>0) values of offset are used to perform several specific actions with the pointers to circbuf data and to wait for the next image to be acquired. Using SEEK_END with offset==0 (or negative) will have no difference to normal implementations, fseek(''file'', 0, SEEK_END) will move the file pointer just after the last byte in the circbuf. All the accesses with SEEK_CUR, SEEK_SET will use the fact that the buffer is circular - the file pointer will just roll over, so fseek (''file'', -2, SEEK_SET) will position the pointer just in front of the 2 last bytes of the circbuf.		*'''SEEK_END''' - move file pointer relative to the end of file, so any positive value of offset moves file pointer beyond the end of file. It is not considered to be an error - normal files can be written to beyond the current file length. This is not applicable to current implementation of the circbuf (it has a fixed size), so the SEEK_END with positive (>0) values of offset are used to perform several specific actions with the pointers to circbuf data and to wait for the next image to be acquired. Using SEEK_END with offset==0 (or negative) will have no difference to normal implementations, fseek(''file'', 0, SEEK_END) will move the file pointer just after the last byte in the circbuf. All the accesses with SEEK_CUR, SEEK_SET will use the fact that the buffer is circular - the file pointer will just roll over, so fseek (''file'', -2, SEEK_SET) will position the pointer just in front of the 2 last bytes of the circbuf.

	The values for symbolic constants described below are defined in the [http://elphel.cvs.sourceforge.net/elphel/elphel353-2.10/os/linux-2.6-tag--devboard-R2_10-4/include/asm-cris/elphel/c313a.h?view=markup include/asm-cris/elphel/c313a.h] header file.		The values for symbolic constants described below are defined in the [http://elphel.cvs.sourceforge.net/elphel/elphel353-7.1/os/linux-2.6-tag--devboard-R2_10-4/include/asm-cris/elphel/c313a.h?view=markup include/asm-cris/elphel/c313a.h] header file.

	"Current pointer" or "selected frame" in the description below references to the file pointer of an opened file. As soon as the /dev/circbuf file is closed (usually happens between individual accesses through the web server), the value of such pointer is lost.		"Current pointer" or "selected frame" in the description below references to the file pointer of an opened file. As soon as the /dev/circbuf file is closed (usually happens between individual accesses through the web server), the value of such pointer is lost.