PR System One Data Format
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Contents
Data format analysis
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.
Contents
PRS1 Data File Format
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
[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
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)
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
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
00 8bit Signed 01 8bit Unsigned
Waveform Data Structure
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)
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
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)
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
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)
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)
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
.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
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 deciphering 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 its accuracy.
If you need to know any details with 100% certainty, I'm sure Philips Respironics will love to answer your questions.. ;)
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