Message Structure

Message assembly from packets

Messages are assembled from one or more packets. Here's an example of a series of packets that make up a temp basal being issued.

First packet from PDM to POD: 1f07b1eeb91f07b1ee30201a0ebee0a2d001007d01384000020002160e40000015051be550 is decoded as ID1:1f07b1ee PTYPE:PDM SEQ:25 Contents:1f07b1ee30321a0ebee0a2d001007d01384000020002160e40000015051be5 CRC:50

Then the POD acks with: 1f07b1ee5a1f07b1ee30

Second packet from PDM to POD is a CON packet 1f07b1ee9b6d0015051be56d8137f3, which is decoded as ID1:1f07b1ee PTYPE:CON SEQ:27 CON:6d0015051be56d8137 CRC:f3

The assembled message from these two packets is thus 1f07b1ee30201a0ebee0a2d001007d01384000020002160e40000015051be56d0015051be56d8137.

Message Structure

Let's break the above message down into parts:

IIIIIIII B9 BL <------------------------ Message Body -------------------------> CRC16
1f07b1ee 30 20 1a0ebee0a2d001007d01384000020002 160e40000015051be56d0015051be56d  8137

• IIIIIIII (Pod ID) (4 bytes): 1f07b1ee. This 32-bit ID is assigned by the PDM at startup and is then used throughout the active life of the Pod for all its subsequence communication with the PDM. This ID is programmed into both the S08 MCU on both the Pod and the PDM as a packet selector.
• B9 (1 byte): 30. Bit format: A0CCCCLL.
  • Bit A (0) if 1 sets a 4 minute alarm in which the pod must receive a non $E command in or else the pod will fail with a $33 fault.
  • Bits CCCC (1100) are a 4-bit message sequence # counter B9-CCCC-counter.
  • Bits LL (00) are the top 2 bits of the 10-bit message body length.
• BL (BLEN) (1 byte): (20= 32) the 2-Bit LL value and the 8-bit BLEN value specify the total 10-bit length of the message body.
• Message Body (variable, up to 1023 bytes total): 1a0ebee0a2d001007d01384000020002 160e40000015051be56d0015051be56d. The message body consists of one or more sub-commands message or a single response message. In this example, there is actually a second 16 sub-command. Each sub-command message or response has the following basic format.
  • The first byte (1a for the 1st sub-command and 16 for the 2nd sub-command) indicates the type of the sub-message
  • The second byte (0e for both sub-commands in this example) is the length of the encoded sub-command (except for the 1d response)
• CRC16 (2 bytes): 8137. This is a pseudo CRC16

The length of the message type + body above is 0x20 bytes, matching the BLEN value.

Message sequence number (CCCC bits of B9 byte)

Message sequence number is usually incremented by PDM and POD. But there are some cases where it is not. For example when nonce fake resync (# is the message sequence):

PDM 1a(14)->Insulin Schedule:Nonce:851072aa(-1) Type:02 Bolus CheckSum:0088/0088 Duration:01(30 minutes) FiledA:0320 UnitRate:0032(2.5U) UnitRateSchedule:0032(2.5U)

PDM 17(13)->InsulinExtra(short):Immediate

POD 06(3)->POD Error:Type:14 Nonce ErrorHx=85ab Seed request :3

PDM 1a(14)->Insulin Schedule:Seed(3)Nonce:436a5bb5(0) Type:02 Bolus CheckSum:0088/0088 Duration:01(30 minutes) FiledA:0320 UnitRate:0032(2.5U) UnitRateSchedule:0032(2.5U)

PDM 17(13)->InsulinExtra(short):Immediate

But appears also when some particular status from POD

PDM 0e(1)->Get Status type 00

POD 02(22)->Resp02:020d00001406077318117f0000117f0000195709030d

PDM 0e(1)->Get Status type 01

POD 02(19)->Resp02:01000000000000000000000000000000000000

PDM 0e(1)->Get Status type 80

POD 02(203)->Resp02:5007733172570134734401397359013c7342014172590144724301497257014c7341015172550154734101597356815c734481617356810073438005725680087343800d7355801073458015735180187346801d734f802073498025735200287344002d7351003072450035725300387243003d7251004073450045725100487344004d7250005072430055724f00587248805d73508060734a8001734e800472448009724e800c72448011724d801473438019724c801c72428021734c002472470029724f002c714900

PDM 0e(1)->Get Status type 81

POD 02(203)->Resp02:5100323172510034724400397252003c7246004173530044724800497251004c7343005173500054724680597253805c734580017254bf047247bf097254bf0c724bbf117253bf147146bf197450bf1c7247bf21734ebf247344bf2973503f2c73473f31734f3f3473493f3972513f3c73483f4172523f4473483f4973523f4c73453f5172523f5473433f5973533f5c7346bf613254bf647345bf0172548104704681097552810c7245811172538114724281197352811c7243812172568124734101297259012c734301

#9 PDM 1c(4)->CancelPOD Nonce 851072aa(-1)

#10 POD 06(3)->POD Error:Type:14 Nonce ErrorHx=85f7 Seed request :35

PDM Message Patterns Examples

Status Packet Exchange

• PDM (0e01) (Status Request)
• POD (1d**) (Status Response)
• ACK

Bolus Packet Exchange

• PDM (0e01) (Status Request)
• POD (1d**) (Status Response)
• ACK
• PDM (1a0e) (Bolus Request)
• ACK
• CON
• POD (1d**) (Status Response)
• CON
• PDM (0e01) (Status Request)
• POD (1d**) (Status Response)
• ACK

Temp Basal Packet Exchange

• PDM (1a0e) (Basal Change Request)
• ACK
• CON
• POD (1d**) (Status Response)
• ACK