On Fri, 2022-05-13 at 11:46 +0200, Devid Antonio Filoni wrote: > Hi David, > > On Wed, 2022-05-11 at 16:22 +0200, David Jander wrote: > > Hi Devid, > > > > On Wed, 11 May 2022 14:55:04 +0200 > > Devid Antonio Filoni < > > devid.filoni@xxxxxxxxxxxxxxxxxxxxx > > > wrote: > > > > > On Wed, 2022-05-11 at 11:06 +0200, David Jander wrote: > > > > Hi, > > > > > > > > On Wed, 11 May 2022 10:47:28 +0200 > > > > Oleksij Rempel < > > > > o.rempel@xxxxxxxxxxxxxx > > > > > > > > > wrote: > > > > > > > > > > > > > Hi, > > > > > > > > > > i'll CC more J1939 users to the discussion. > > > > > > > > Thanks for the CC. > > > > > > > > > On Tue, May 10, 2022 at 01:00:41PM +0200, Devid Antonio Filoni wrote: > > > > > > Hi, > > > > > > > > > > > > On Tue, 2022-05-10 at 06:26 +0200, Oleksij Rempel wrote: > > > > > > > Hi, > > > > > > > > > > > > > > On Mon, May 09, 2022 at 09:04:06PM +0200, Kurt Van Dijck wrote: > > > > > > > > On ma, 09 mei 2022 19:03:03 +0200, Devid Antonio Filoni wrote: > > > > > > > > > This is not explicitly stated in SAE J1939-21 and some tools used for > > > > > > > > > ISO-11783 certification do not expect this wait. > > > > > > > > > > > > > > It will be interesting to know which certification tool do not expect it and > > > > > > > what explanation is used if it fails? > > > > > > > > > > > > > > > IMHO, the current behaviour is not explicitely stated, but nor is the opposite. > > > > > > > > And if I'm not mistaken, this introduces a 250msec delay. > > > > > > > > > > > > > > > > 1. If you want to avoid the 250msec gap, you should avoid to contest the same address. > > > > > > > > > > > > > > > > 2. It's a balance between predictability and flexibility, but if you try to accomplish both, > > > > > > > > as your patch suggests, there is slight time-window until the current owner responds, > > > > > > > > in which it may be confusing which node has the address. It depends on how much history > > > > > > > > you have collected on the bus. > > > > > > > > > > > > > > > > I'm sure that this problem decreases with increasing processing power on the nodes, > > > > > > > > but bigger internal queues also increase this window. > > > > > > > > > > > > > > > > It would certainly help if you describe how the current implementation fails. > > > > > > > > > > > > > > > > Would decreasing the dead time to 50msec help in such case. > > > > > > > > > > > > > > > > Kind regards, > > > > > > > > Kurt > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The test that is being executed during the ISOBUS compliance is the > > > > > > following: after an address has been claimed by a CF (#1), another CF > > > > > > (#2) sends a message (other than address-claim) using the same address > > > > > > claimed by CF #1. > > > > > > > > > > > > As per ISO11783-5 standard, if a CF receives a message, other than the > > > > > > address-claimed message, which uses the CF's own SA, then the CF (#1): > > > > > > - shall send the address-claim message to the Global address; > > > > > > - shall activate a diagnostic trouble code with SPN = 2000+SA and FMI = > > > > > > 31 > > > > > > > > > > > > After the address-claim message is sent by CF #1, as per ISO11783-5 > > > > > > standard: > > > > > > - If the name of the CF #1 has a lower priority then the one of the CF > > > > > > #2, the the CF #2 shall send its address-claim message and thus the CF > > > > > > #1 shall send the cannot-claim-address message or shall execute again > > > > > > the claim procedure with a new address > > > > > > - If the name of the CF #1 has higher priority then the of the CF #2, > > > > > > then the CF #2 shall send the cannot-claim-address message or shall > > > > > > execute the claim procedure with a new address > > > > > > > > > > > > Above conflict management is OK with current J1939 driver > > > > > > implementation, however, since the driver always waits 250ms after > > > > > > sending an address-claim message, the CF #1 cannot set the DTC. The DM1 > > > > > > message which is expected to be sent each second (as per J1939-73 > > > > > > standard) may not be sent. > > > > > > > > > > > > Honestly, I don't know which company is doing the ISOBUS compliance > > > > > > tests on our products and which tool they use as it was choosen by our > > > > > > customer, however they did send us some CAN traces of previously > > > > > > performed tests and we noticed that the DM1 message is sent 160ms after > > > > > > the address-claim message (but it may also be lower then that), and this > > > > > > is something that we cannot do because the driver blocks the application > > > > > > from sending it. > > > > > > > > > > > > 28401.127146 1 18E6FFF0x Tx d 8 FE 26 FF FF FF FF FF FF //Message > > > > > > with other CF's address > > > > > > 28401.167414 1 18EEFFF0x Rx d 8 15 76 D1 0B 00 86 00 A0 //Address > > > > > > Claim - SA = F0 > > > > > > 28401.349214 1 18FECAF0x Rx d 8 FF FF C0 08 1F 01 FF FF //DM1 > > > > > > 28402.155774 1 18E6FFF0x Tx d 8 FE 26 FF FF FF FF FF FF //Message > > > > > > with other CF's address > > > > > > 28402.169455 1 18EEFFF0x Rx d 8 15 76 D1 0B 00 86 00 A0 //Address > > > > > > Claim - SA = F0 > > > > > > 28402.348226 1 18FECAF0x Rx d 8 FF FF C0 08 1F 02 FF FF //DM1 > > > > > > 28403.182753 1 18E6FFF0x Tx d 8 FE 26 FF FF FF FF FF FF //Message > > > > > > with other CF's address > > > > > > 28403.188648 1 18EEFFF0x Rx d 8 15 76 D1 0B 00 86 00 A0 //Address > > > > > > Claim - SA = F0 > > > > > > 28403.349328 1 18FECAF0x Rx d 8 FF FF C0 08 1F 03 FF FF //DM1 > > > > > > 28404.349406 1 18FECAF0x Rx d 8 FF FF C0 08 1F 03 FF FF //DM1 > > > > > > 28405.349740 1 18FECAF0x Rx d 8 FF FF C0 08 1F 03 FF FF //DM1 > > > > > > > > > > > > Since the 250ms wait is not explicitly stated, IMHO it should be up to > > > > > > the user-space implementation to decide how to manage it. > > > > > > > > I think this is not entirely correct. AFAICS the 250ms wait is indeed > > > > explicitly stated. > > > > The following is taken from ISO 11783-5: > > > > > > > > In "4.4.4.3 Address violation" it states that "If a CF receives a message, > > > > other than the address-claimed message, which uses the CF’s own SA, then the > > > > CF [...] shall send the address-claim message to the Global address." > > > > > > > > So the CF shall claim its address again. But further down, in "4.5.2 Address > > > > claim requirements" it is stated that "...No CF shall begin, or resume, > > > > transmission on the network until 250 ms after it has successfully claimed an > > > > address". > > > > > > > > At this moment, the address is in dispute. The affected CFs are not allowed to > > > > send any other messages until this dispute is resolved, and the standard > > > > requires a waiting time of 250ms which is minimally deemed necessary to give > > > > all participants time to respond and eventually dispute the address claim. > > > > > > > > If the offending CF ignores this dispute and keeps sending incorrect messages > > > > faster than every 250ms, then effectively the other CF has no chance to ever > > > > resume normal operation because its address is still disputed. > > > > > > > > According to 4.4.4.3 it is also required to set a DTC, but it will not be > > > > allowed to send the DM1 message unless the address dispute is resolved. > > > > > > > > This effectively leads to the offending CF to DoS the affected CF if it keeps > > > > sending offending messages. Unfortunately neither J1939 nor ISObus takes into > > > > account adversarial behavior on the CAN network, so we cannot do anything > > > > about this. > > > > > > > > As for the ISObus compliance tool that is mentioned by Devid, IMHO this > > > > compliance tool should be challenged and fixed, since it is broken. > > > > > > > > The networking layer is prohibiting the DM1 message to be sent, and the > > > > networking layer has precedence above all superior protocol layers, so the > > > > diagnostics layer is not able to operate at this moment. > > > > > > > > Best regards, > > > > > > > > > > > > > > Hi David, > > > > > > I get your point but I'm not sure that it is the correct interpretation > > > that should be applied in this particular case for the following > > > reasons: > > > > > > - In "4.5.2 Address claim requirements" it is explicitly stated that > > > "The CF shall claim its own address when initializing and when > > > responding to a command to change its NAME or address" and this seems to > > > > The standard unfortunately has a track record of ignoring a lot of scenarios > > and corner cases, like in this instance the fact that there can appear new > > participants on the bus _after_ initialization has long finished, and it would > > need to claim its address again in that case. > > > > But look at point d) of that same section: "No CF shall begin, or resume, > > transmission on the network until 250 ms after it has successfully claimed an > > address (Figure 4). This does not apply when responding to a request for > > address claimed." > > > > So we basically have two situations when this will apply after the network is > > up and running and a new node suddenly appears: > > > > 1. The new node starts with a "Request for address claimed" message, to > > which your CF should respond with an "Address Claimed" message and NOT wait > > 250ms. > > > > or > > > > 2. The new node creates an addressing conflict either by claiming its address > > without first sending a "request for address claimed" message or (and this is > > your case) simply using its address without claiming it first. > > > > It is this second possibility where there is a conflict that must be resolved, > > and then you must wait 250ms after claiming the conflicting address for > > yourself. > > > > > completely ignore the "4.4.4.3 Address violation" that states that the > > > address-claimed message shall be sent also when "the CF receives a > > > message, other than the address-claimed message, which uses the CF's own > > > SA". > > > Please note that the address was already claimed by the CF, so I think > > > that the initialization requirements should not apply in this case since > > > all disputes were already resolved. > > > > Well, yes and no. The address was claimed before, yes, but then a new node came > > onto the bus and disputed that address. In that case the dispute needs to be > > resolved first. Imagine you would NOT wait 250ms, but the other CF did > > correctly claim its address, but it was you who did not receive that message > > for some reason. Now also assume that your own NAME has a lower priority than > > the other CF. In this case you can send a "claimed address" message to claim > > your address again, but it will be contested. If you don't wait for the > > contestant, it is you who will be in violation of the protocol, because you > > should have changed your own address but failed to do so. > > > > > - If the offending CF ignores the dispute, as you said, then the other > > > CF has no chance to ever resume normal operation and so the network > > > cannot be aware that the other CF is not working correctly because the > > > offending CF is spoofing its own address. > > > > Correct. And like I said in my previous reply, this is unfortunately how CAN, > > J1939 and ISObus work. The whole network must cooperate and there is no > > consideration for malign or adversarial actors. > > There are also a lot of possible corner cases that these standards > > unfortunately do not take into account. Conformance test tools seem to be even > > more problematic and tend to have bugs quite often. I am still inclined to > > think this is the case with your test tool. > > > > > This seems to make useless the > > > requirement that states to activate the DTC in "4.4.4.3 Address > > > violation". > > > > The requirement is not useless. You can still set and store the DTC, just not > > broadcast it to the network at that moment. > > > > Best regards, > > > > > > Thank you for your feedback and explanation. > I asked the customer to contact the compliance company so that we can > verify with them this particular use-case. I want to understand if there > is an application note or exception that states how to manage it or if > they implemented the test basing it on their own interpretation and how > it really works: supposing that the test does not check the DM1 > presence, then the test could be passed even without sending the DM1 > message during the 250ms after the adress-claimed message. > > Best regards, > Devid Hi David, all, I'm sorry for resuming this discussion after a long time but I noticed that the driver forces the 250 ms wait even when responding to a request for address-claimed which is against point d) of ISO 11783-5 "4.5.2 Address claim requirements": No CF shall begin, or resume, transmission on the network until 250 ms after it has successfully claimed an address (see Figure 4), except when responding to a request for address-claimed. IMHO the driver shall be able to detect above condition or shall not force the 250 ms wait which should then be implemented, depending on the case, on user-space application side. Thank you, best regards, Devid
