System One

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Data format analysis[bewerken | brontekst bewerken]

Grade: B

Negatives

  • Manufacturer failed to openly document this relatively complex data format.
  • A little stingy with the flow waveform resolution, only 5hz.

Positives

  • Space saving data format.
  • Summary data contains settings info for each session, like humidifier, flex settings, etc..
  • Keeps all flow waveform data, unless the card is left out, in which case it retains Event, general graphs & Summary data.
  • Events syncs well over flow waveform.

This is probably the best of the bunch as far as CPAP storage systems go - I say this mainly because they bothered to design it around a decent per-session model, and the machine doesn't unnecessarily wipe out data while it has a mostly empty SD card. Plus accidentally leaving out the SD card doesn't suck anywhere near as much as when it's done on others machines.

PRS1 Data File Format[bewerken | brontekst bewerken]

Each PR System One data file has a well defined structure containing a sequence of one or more data blocks. Each block begins with a 15 byte header, any additional header data, an 8 bit header checksum, the data stream itself (in a not-so-well-defined structure), followed by a 16bit data integrity checksum.

The cycle repeats for each subsequence block, although only waveform data has been observed to contain multiple blocks.

The file's extension provides an extra indication of the type of data contained:

Extension	Type
.001   		Session Summary
.002		Event Data
.004		Time details ???
.005		Waveform Data

The filename component minus the extension gives session sequence number. In most cases it would be better to use the internal values instead, but the are handy for quick lookup.

Standard PRS1 Header Example[bewerken | brontekst bewerken]

[02] [48 0d] [00] [05] [00] [02] [1f 00 00 00] [15 ae 12 4e]

Idx	Data		Type		Details
00 	[02] 		8bit integer	DataFormatVersion
01	[48 0d] 	16bit integer	BlockLength (in bytes, including header & checksum values)
03	[00] 		8bit integer	FileType (Defining additional header information)
04	[05] 		8bit integer	Family
05	[00] 		8bit integer	Family Version
06	[02] 		8bit integer	File Extension
07	[1f 00 00 00] 	32bit integer	Session Sequence Number
0b	[15 ae 12 4e]	32bit integer 	TimeStamp (UNIX Epoch)

Known FileType values[bewerken | brontekst bewerken]

00 indicates no additional header data is needed. The standard header is just followed by the 8bit checksum at position 0x0f, which is additive sum of all header values up to this byte.

01 indicates waveform data storage.

Waveform Data Header (.005 files)[bewerken | brontekst bewerken]

Idx	Data		Type		Details
0x0f  	[xx xx]		16bit integer	Number of seconds
0x11	[01]		8bit integer	Unknown
0x12	[xx xx]		16bit integer	Number of signals (nsig)

Followed by a list containing (nsig * 24bits) of data describing how each waveform data is stored:

0x14    [xx xx] 	16bit integer 	Sample interleave
0x16	[xx]		8bit integer	Sample format
.. repeats (nsig times)

Important: For some reason, this list is stored in reverse order.

Followed by the 8bit sum of all header information, stored at 0x16+(nsig*3)

Calculating just the size of a blocks data area[bewerken | brontekst bewerken]

DataSize = BlockLength – HeaderLength – Extra Header stuff – 1 byte header checksum – 2 byte block checksum

For summary & event data, this translates to DataSize = BlockLength-18 For waveform data, this translates to DataSize = BlockLength-18-(nsig*3)

Known Sample Formats[bewerken | brontekst bewerken]

00 	8bit Signed
01	8bit Unsigned

Waveform Data Structure[bewerken | brontekst bewerken]

If only one waveform is present (indicated by number of signals == 1), this simply contains DataSize/SampleSize samples for this block in order.

If more than one waveform is present, the data is multiplexed together in small groups of samples, the size of which is determined by the interleave value and sample type stored in the header.

Only 8 bit samples have been observed, but I feel it's safe to assume the interleave counts samples and not bytes. Different sample types can be interleaved together, and may therefore be different sizes.

Note: Interleaved data is stored in the opposite order to the list data defined in the waveform header component.

Example, Two multiplexed waveforms, one with an interleave of 5, sample type 0, and the other has an interleave of 5, sample type 1

Byte 	Value 	Waveform
0x00 	44 	1 		(Starting from the first byte in the data block)
0x01 	45 	1
0x02 	46 	1
0x03 	48 	1
0x04 	50 	1
0x05 	00 	2
0x06 	01 	2
0x07 	02 	2
0x08 	03 	2
0x09 	04 	2
0x0a 	55 	1
0x0b 	55 	1
0x0c 	55 	1
0x0d 	55 	1
0x0e 	55 	1
0x0f 	05 	2
... and so on.. 

Interleaving repeats for the remainder of the DataSize

Event Data Format (.002 files)[bewerken | brontekst bewerken]

Event data is stored after the standard header in time-delta format.

Each event is represented by an 8bit code, and generally followed by 16bits worth of delta offset values, and zero or more data fields of varying byte lengths, determined by the event code.. (I say generally because occasionally events have a short form based on the content.)

The schema describing this information is not stored with the event data, so understanding of the DataFormat, Family & Family Version fields is needed to interpret this file correctly.

System One ASV Data (family 5) for instance, uses different codes than a System One Remstar Auto (family 0) ASV does not contain RERA (or at least according to Philips Respironics Encore software, you'd think their top of the line machine would have this if it wasn't a bullshite figure to begin with.)

Family 0 Codes[bewerken | brontekst bewerken]

Code	Name		Delta	Data Fields		        Notes
0x01	Unknown	        [xx xx] No data records
0x02	Pressure	[xx xx] Pressure=[xx] 		        Divide pressure value by 10
0x03	BIPAP Press.	[xx xx] EPAP=[xx]  IPAP=[xx]   	        Divide pressure values by 10
0x04	PressurePulse	[xx xx] Unknown=[xx] 
0x05	RERA		[xx xx] Offset=[xx]
0x06	Obstructive	[xx xx] Offset=[xx]
0x07	ClearAirway	[xx xx] Offset=[xx]
0x0a 	Hypopnea	[xx xx] Offset=[xx]
0x0c	FlowLimitation  [xx xx] Offset=[xx]
0x0d	Vsnore		[xx xx] No data records
0x0e 	Unknown	        [xx xx] [xx] [xx] [xx]			Unknown purpose
0x0f	CSR/PB	        [xx xx] Duration=[xx xx] Offset=[xx]	
0x11	GraphData	[xx xx] Leak=[xx] Snore=[xx]
0x12 	Summary?	?????	[xx] [xx] [xx] [xx]

Family 5 Codes (ASV)[bewerken | brontekst bewerken]

Code	Name		Delta	Data Fields		Notes
0x00 	Unknown	        Variable length.. 		Freaking weird. Read all the zeros in sequence, and then one more value.
0x02	Pressure	[xx xx] Pressure=[xx]		Divide pressure value by 10
0x04	PressurePulse?	[xx xx] ?? = [xx]		This data looks like pressure pulse.
0x05	Obstructive	[xx xx] Offset=[xx]
0x06	ClearAirway	[xx xx] Offset=[xx]
0x07 	Hypopnea	[xx xx] Offset=[xx]
0x09	FlowLimitation  [xx xx] Offset=[xx]
0x0b	CSR/PB	        [xx xx] Duration=[xx xx] Offset=[xx]	Multiply Duration by 2
0x0d	GraphData	[xx xx] [xx xx xx xx xx xx xx xx xx xx]	These 10 bytes are broken down further into graph data
0x0e  	Unknown	        [xx xx] [xx]			Unknown Purpose.. RERA?

Delta values are applied before adding the event. Offset values are subtracted from the running delta (but they don't adjust the running delta, only the individual event)

Example 0x0d GraphData breakdown[bewerken | brontekst bewerken]

0d [78 00] [50] [50] [51] [1d] [13] [64] [0d] [44] [00] [2e]
      0     1    2    3    4    5    6    7    8    9    10

Idx	Details						Notes
00 	The usual 16bit Time-Delta  
01 	IPAP Value					Divide by 10
02 	IPAP Low Range					Divide by 10
03 	IPAP High Range					Divide by 10
04 	Leak
05 	Breaths Per Minute 
06 	Patient Triggered breaths %
07 	Minute Ventilation
08 	Tidal Volume   / 10.0 				Multiply by 10
09 	Snore Graph					(>0 = event flag on encore) 
10 	EPAP Value					Divide by 10

IPAP High – IPAP Low = PS (Pressure Support)? IPAP – EPAP = Pressure Support?

Summary Data (.001 files)[bewerken | brontekst bewerken]

Summary data is stored after a standard data header, and contain totals, pressure settings, and general machine settings for a recorded session. Usually they are around 77 bytes, although this varies. multiple sessions can be contained in the one file.

The structure is messy and not well defined, nor is it well understood

A non zero value in the 6th data position inserts 4 bytes directly afterwards..

See sleepyhead code for definitions.

[ STILL TO DO ]

Summary Data (.000 files)[bewerken | brontekst bewerken]

These are the only "data" files recorded by brick machines.. (250P and below.. this includes the infamous "Plus" model)

they only contain very basic compliance information.

They are usually 44 bytes in size, unless they contain multiple sessions

They contain a rough usage time for each session, a pressure setting, c-flex setting, and humidifier setting. (Plus probably a few other machine on/off typed settings)

Nothing particularly USEFUL is recorded here.

These machines should be BANNED!

.004 files[bewerken | brontekst bewerken]

.004 files are short, and contain a standard header, followed by a data area containing not fully known information

Example Contents

07 [d3 ef 0a 4b] 17 87 08 00 35 [26 8e 0a 4b] 29 7b 08 00

The two 32bit values in brackets are obviously timestamps.

Information about this Document[bewerken | brontekst bewerken]

This document was compiled and written by Mark Watkins <jedimark>

This knowledge contained in this document represents the combined work of several hackers of the CPAPTalker's community.

Credit especially goes to Mike Hoolehan (see http://www.onkor.net) for the initial grokking into this weird and wonderful data format.

I expanded on this work by decyphering the ASV stuff and the remainder of the waveform headers.

Any terminology about Philips Respironics Trademarks belongs to them, (things like Flex types, machine and model names, etc..)

The author along with this work is in no way affiliated with Philips Respironics.. Just a hacker with OSA and an earnest desire to understand how CPAP machines (and the related health conditions) work.

This data format was lawfully reverse engineered by experienced hackers studying the raw SD card data very carefully. No guarantees are made regarding it's accuracy.

If you need to know any details with 100% certainty, I'm sure Philips Respironics will love to answer your questions.. ;)