= M-Stream 2.3 =

* [[MStream_ChangeLog]]

M-Stream data has packet structure. Large packets may be split to fragments with same Packet ID to fit in encapsulating frame.

M-Stream 2.0 defines M-Stream Header, Event Header and User Payload data objects. In fragmentation process, M-Stream Header is persistent and should be present in all fragments. Event Header should be present in first fragment only.


||<-32 rowclass="bits">M-Stream Header||
||<:>word #||<:>byte offset||<:>bits||<:>description||
||<:|4>0||<:|4>0||31:24||[[DeviceId|Device ID]]||
||23:18||Flags||
||17:16||Subtype||
||15:0||Fragment length||
||<:|2>1||<:|2>4||31:16||Packet ID||
||15:0||Fragment offset code||

||<-3 rowclass="bits">Flags bits||
||bit||value||
||5||LF(last fragment)||
||4||EVC (Event Complete)||
||3||FIN ''(not used yet)''||
||2||SYN ''(not used yet)''||
||1||RST ''(not used yet)''||
||0||ACK||

Fragment length is defined as number of bytes starting at offset 8. For M-Stream frame of size N 32-bit words, fragment length value is 4*(N-2).

Fragment offset code is number of 64-byte blocks. Fragmentation is performed at 64-byte block boundary (compare to 8 bytes in IP fragmentation).

Fragmentation supports maximum of 64*2^16 = 4 MByte data payloads.

Fragment ID is 16-bit number (0-65535).

Flags:
 * LF - last part of current fragment (<Fragment length>+<Fragment offset code> = <Full length of this fragment>)
 * EVC - last part of current event (One sets with LF flag for last channel in current event)
 * ACK - acknowledge flag: is set in MStream receiver program to inform device of reciecing package which contains fragment with corresponding FragmentId and FragmentOffset

== Subtype 0: Trigger and User Data ==

||<-32 rowclass="bits">M-Stream Header||
||<:>word #||<:>byte offset||<:>bits||<:>description||
||<:|4>0||<:|4>0||31:24||[[DeviceId|Device ID]]||
||23:18||Flags||
||17:16||Subtype (0)||
||15:0||Fragment length, 4*(N-2)||
||<:|2>1||<:|2>4||31:16||Packet ID||
||15:0||Fragment offset code||
||<-32 rowclass="bits">Subtype 0 Header||
||<:>2||<:>8||31:0||Device serial number||
||<:|2>3||<:|2>12||31:24||Subtype and custom bits||
||23:0||Event number||
||<-32 rowclass="bits">M-Stream Subtype 0 Payload||
||<:>4||<:>16||31:0||Event timestamp, TAI seconds||
||<:|2>5||<:|2>20||31:2||Event timestamp, TAI nanoseconds||
||1:0||Event timestamp, TAI flags||
||<:>6||<:>24||31:0||<|3>User defined payload||
||<:-3>...||
||<:>N-1||<:>4*(N-1)||31:0||

TAI flags: 2 - timecode is valid, otherwise invalid.

== Subtype 1: User Data, Channel-Based Readout ==

||<-32 rowclass="bits">M-Stream Header||
||<:>word #||<:>byte offset||<:>bits||<:>description||
||<:|4>0||<:|4>0||31:24||[[DeviceId|Device ID]]||
||23:18||Flags||
||17:16||Subtype (1)||
||15:0||Fragment length, 4*(N-2)||
||<:|2>1||<:|2>4||31:16||Packet ID||
||15:0||Fragment offset code||
||<-32 rowclass="bits">Subtype 1 Header||
||<:>2||<:>8||31:0||Device serial number||
||<:|2>3||<:|2>12||31:24||Channel number||
||23:0||Event number||
||<-32 rowclass="bits">M-Stream Subtype 1 Payload||
||<:>4||<:>16||31:0||<|3>User defined payload||
||<:-3>...||
||<:>N-1||<:>4*(N-1)||31:0||

== Subtype 2: User Data, Time Slice Based Readout ==

||<-32 rowclass="bits">M-Stream Header||
||<:>word #||<:>byte offset||<:>bits||<:>description||
||<:|4>0||<:|4>0 ||31:24||[[DeviceId|Device ID]]||
||                 23:18||Flags||
||                 17:16||Subtype (1)||
||                 15:0 ||Fragment length, 4*(N-2)||
||<:|2>1||<:|2>4 ||31:16||Packet ID||
||                 15:0 ||Fragment offset (bytes)||
||<-32 rowclass="bits">Subtype 2 Header||
||<:>2  ||<:>8   ||31:0 ||Device serial number||
||<:>3  ||<:>12  ||31:0 ||reserved||
||<-32 rowclass="bits">M-Stream Subtype 2 Payload||
||<:>4  ||<:>24  ||31:0 ||<|3>User defined payload||
||<:-3>...              ||
||<:>N-1||<:>4*(N-1)||31:0||

== Acknowledge ==

Acknowledge package is similar to standard M-Stream package.
First 32-bit word should have acknowledge bit up 22^nd^ bit, as described in ''Flag'' field in [[MStream_2_0|M-Stream ver. 2.0]].
All following word will be proceeded as ''Fragment Id'' and ''Fragment Offset'' pairs. One package can contain one acknowledge pair (by default) or several (request M-Stream configuration register in [[MlinkCsr|M-Link CSR]]).
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[[CategoryMlink|MLink]] [[CategoryMStream|MStream]] [[CategoryRawData|RawData]]