Read a lot of specifications and still can't get a simple thing.
All UDS requests encapsulated in ISO-TP packets, which are encapsulated in simple CAN frames, so ECU constantly receives a stream of frames from CAN bus.
How does ECU decide that this CAN frame is a part of any high-level protocol?
For example, I've sent Security request to ECU, CAN frame data will look like this
02 27 01
How does ECU determine that this is not just a chunk of data but a part of the protocol?
I wasn't able to find any relation to ISO/OSI stack when high-level protocols "talk to each other" using headers, so we know how to decode data packets.
The CAN message IDs that are used for specific protocols are defined per system.
In most cases the OBD-II will be sent over CAN ID 7DFh for the query and higher IDs for responses from different modules, but even that might be different on specific car models.
One way of figuring out the CAN IDs that are used for UDS-based communication is to send simple tester-present (SID 3Eh) messages and watching for CAN IDs which seems to have an appropriate response.
UDS via CAN is specified in the DoCAN ISO-15765-2 part and describe the network and transport layer for a functional (broadcast) and physical (p2p) communication between ECUs or better control functions.
Normal CAN id's don't implement any network functionalities like a addressing. For that purpose the SAE J1939 network layer is used. In a J1939 network each CAN client has a address and each functionality a parameter group (PGN). All of this is encoded in a 29bit CAN ID. For example the CAN ID 0x18EF8081. This will transport a message from the CAN client 0x81 to 0x80 via the PGN 0xEF, 0x18 is the priority.
In UDS over CAN the PGNs 0xDA (physical) and 0xDB (functional) are used for all communications. With that information's you can implement a CAN ID filter which match only the PGN part of the CAN ID.
Related
After that I send different runicast messages with the function runicast_send, how can I understand which message was acknowledged when the callback sent_runicast is triggered?
The runicast.h file states:
The runicast primitive adds two packet attributes: the single-hop
packet type and the single-hop packet ID. The runicast primitive
uses the packet ID attribute as a sequence number for matching
acknowledgement packets to the corresponding data packets.
but I didn't understand how to do it in practice. Can somebody provide an example?
One way would be to look at the field sndnxt of struct runicast_conn *c before you send the packet, and then compare that value of the packetbuf_attr(PACKETBUF_ATTR_PACKET_ID) in the "sent" callback of your code.
However note that by default the runicast packet ID is just 2 bits long. Enough to demultiplex the ACK in most cases, but may be insufficient for your purposes. (The packet ID size in bits can be changed by redefining RUNICAST_PACKET_ID_BITS.)
Also Rime is obsolete. Don't use it in your code, especially production code unless you know what you're doing. runicast was never one of the highlights of Rime, I doubt there are no better alternatives (e.g. the uIPv6 stack) for what you want to do.
I have a huge pcap file. I want to know facebook usage in terms of data transfered (upload, download). For that, I am using wireshark to read this file. From a question on stackoverflow , there are many fields that can be used to find bytes.
frame.len==243
ip.len=229
udp.length==209
data.len=201
Now, I have test frame.len and ip.len both gives different results. What I should consider correct ? I am a newbie in networks terminology and I have to just find correct data transfered.
What happens, when you connects to server and requests some simple page:
Server application generates requested data (e.g. <body>Hello world</body> string) and passes it to HTTP layer
HTTP layer generates necessary header according to RFC (specifies HTTP version, status code, content type etc), prepends it to generated data and pass everything to TCP layer
TCP layer may break data into more than one pieces (not our case, message is already too small) and prepend necessary info for transport layer to each piece (src/dst port number, sequence number, some flags, checksum etc), then passes it to IP level
IP layer prepends necessary info for routing (source/dest addresses, TTL and other stuff), then passes it to lower layer (e.g. Ethernet)
Ethernet adds its part (MAC addresses, maybe VLAN tags) and pushes all to physical device
Resulted data is sent byte-by-byte from server's NIC to network
So your question is actually up to you. What do you want to measure? Is it "data, which I need to display excluding all auxiliary info"? Or is it "all number of bytes I need to send/receive for getting this lovely cat picture"? Here is a list of fields to get size of each part:
To get data lenght only (as string, unfortunately): http.content_length_header == "606"
To get (data + HTTP header) length: tcp.len == 973
To get (data + HTTP + TCP + IP layers): ip.len=1013
To get every byte sent: frame.len == 1027
If you want to measure bandwidth occupation, use frame.len. If you're interested in "pure site weight", it should be independent from environment, so use http.content_length_header. Things might become more complicated on high level considering the following:
Era of HTTPS means you can't easily observe HTTP content in traces, so tcp.len might be the highest option
Some data (e.g. audio, video) is transferred over different protocol stack (e.g. IP - UDP - RTP)
I basically understand the concept of PDO mapping in CANopen networks. It allows to to broadcast real-time data with small header.
how it is made? How do I setup my devices to know how to send/receive PDO's? Do I need some kind of software for that?
A lot the answers to your questions depend on the specific devices you are using, but in general...
Do I need some kind of software for that?
You do not need specialized software to configure a CANopen device. They can be configured over CANbus using SDOs. A USB CANbus dongle is more than sufficient although manuually constructing SDOs is tedious. Companies exist that provide software to configure any CANopen device e.g. Vector. Often vendors will provide a specialized GUI to configure their devices e.g. AMC's DriveWare. If one is available you should probably use it.
How is it made?
PDOs (Process Data Objects) in contrast to SDOs (Service Data Objects) do not include meta-data about the contents of the message and TPDOs may be transmitted without a specific request from the master. This allows PDOs to use the bus more efficiently. The trick is that the contents of PDO messages must be agreed upon ahead of time. This agreement is specified using the PDO Communications Parameters and PDO Mapping Parameters entries of your devices Object Dictionary. How they may be configured or if they can be configured at all is device dependent. Most commonly PDOs can be configured at run-time during pre-operational mode through SDOs. Though this may be (and is likely to be) unnecessary if the defaults provided by your device are sufficient.
The contents of a PDO is configured through its corresponding "Mapping Parameters" in the devices Object Dictionary. TPDO Mapping parameters start at index 0x1A00. TPDO0 corresponds to 0x1A00, TPDO1 to 0x1A01 etc.
The mappings are held in the sub-indexes and are encoded as 32-bit unsigned integers. The format is first the 16-bit index then the 8-bit sub-index and lastly the size in bits of the parameter to use. The granularity of the size is device dependent. Some may only provide byte level granularity. E.g. if you had a REAL32 variable in the object dictionary at 0x2000,0x02 you wanted sent as the only parameter of TPDO0 you would set 0x1A00,0x01 to 0x20000220. RPDOs are configured in the same fashion with their indexes starting at 0x1600.
The next piece in the puzzle are the communication parameters. RPDOs usually do not need to be configured in this fashion. TPDOs do need configuration. The indexes start at 0x1800 and correspond to the TPDOs in the same fashion as the mapping parameter indexes.
COBID (0x01) UNSIGNED32 Arbitration/COB-ID PDO will use.
XMIT_TYPE (0x02) UNSIGNED8 When PDO is transmitted
INHIBIT_TIME (0x03) UNSIGNED16 Minimum time between PDO messages (useconds)
EVENT_TIME (0x05) UNSIGNED16 Timeout for sending (mseconds)
PDO message layout takes the associated TPDOnCOMPARAM,COBID for the arbitration ID and appends each of the mapped parameters from TPDOnMAPPARAMS. For TPDOs this is done internally by the device and is sent. For RPDOs the master does this, sends the PDO and device decodes the message writing each parameter to its Object Dictionary.
How do I setup my devices to know how to send/receive PDO's?
The default connection set includes four TPDOs (transmitted from node), and four RPDOs (received by node). More can be specified (up to 512 each) depending on your device.
PDOs are only transmitted/received when a CANopen node is brought into "Operational Mode". To do this you need to send an NMT (Network ManagemenT) start command (Code Specifier = 1). Using 0 for the node ID indicates a broadcast message that all nodes will respond to.
NMT Messages:
Have a COB-ID of 0
Have a payload of 2 bytes
NMT Message Format (CAN-bus payload):
+--------------------------+
| Code Specifier | Node ID |
+----------------+---------+
| ff | ff |
+----------------+---------+
How a CAN Bus controller decides based on message identifier that this particular message belongs to it?Is it like the receiver already know that if identifier has suppose value 5 then its for me . And we program receiver to tell it that you should be interested in value 5 ?
The software in the CAN node must decide what message IDs it is interested in, based on the network specification which is usually some kind of document or other electronic representation of which messages contain what sorts of information. If a message arrives that is of no interest, it simply does not process it and the software returns to what it was doing just before the message arrived (assuming interrupt driven CAN handling).
Some CAN controllers (ie the part of the chip which does the CAN protocol transmission and reception) have message filtering which means that uninteresting messages can be dropped before they reach the software. Other controllers have message filtering which can be set to accept only a single message ID in a particular "message box", and these can be configured to accept the messages you are interested in. Again, other messages are dropped. Some controllers have both filters and message boxes.
At the CAN protocol level all nodes in a CAN network are equal and make a decision about whether to process a message or not. A "CAN controller" is a higher-level concept; it still needs to examine the message identifier like any other node.
Note that "processing" a message is different to the CAN protocol message check and acknowledgement. All nodes take part in that processing unless they're in "listen only" mode.
Update:
How you decide which message to process depends on what you are trying to do and the higher level protocol in use over CAN. In principle you mask out the ID bits that are relevant and then test them to see whether the message should be processed.
For example if you want to process all messages with 5 (binary 0101) in the low order four bits, your mask is 15 (binary 1111), you binary-and this with the received message ID, and then you compare the result with five.
For example:
(msg_id & 15) == 5
is a way of coding that test. Which bits you care about, and your implementation details depend on many other factors.
Specifically for PDU1 (Protocol Data Unit) messages, a destination address is specified (byte 3). If a device receives a message not addressed to it, it can simply ignore it. Addresses are assigned by various standards, or a manufacturer may assign them ad-hoc.
In the general case the CAN-ID (bytes 0-4) contains all the details about what kind of message it is, and devices can inspect particular fields to decide whether they care about the message. For example the transmission controller probably doesn't care about battery status messages, nor the fuel gauge about which doors are locked.
I have some problems whiling using Mircosoft Native Wifi API.
I can use queryinterface function to get the current value of counter to know the frames received.
But the statistic involves not only MSDU but also MMPDU and MPDU, which cause the result inaccurate.
as the link: See the site
The members of this structure are used to record MAC-level statistics for:
MAC service data unit (MSDU) packets.
MAC protocol data unit (MPDU) frames.
MPDU frame counters must include all MPDU fragments sent for an MSDU packet.
Management MPDU (MMPDU) frames.
So, is there any way to obtain only the received number of MSDU ??? THX!!