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| <== Date ==> | <== Thread ==> |
|---|
| Subject: | RE: garbage in zero length arrays |
| From: | "Mezger Anton Christian" <[email protected]> |
| To: | "Hill, Jeff" <[email protected]> |
| Cc: | [email protected] |
| Date: | Mon, 20 Jan 2014 08:22:13 +0100 |
Hello Jeff, · The issue is not only with caget but also in application programs getting data through monitor and the routine ca_add_event_array to get the data. · I do not know now about other record types. The record used is the following: § Record(waveform, “$(NAME)”) {field(FTVL, “CHAR”) field(NELM, “128”) field(SCAN, “1 second”)} in softioc. · Caget reports for .NORD 0. Caget gives 128 characters back with first character as garbage. Caget –c does not give any value back. Ca_add_event array gives 128 characters back while 128 were requested with first character as garbage · The behavior stays the same after new subscriptions · I work with 3.14.12. However when specifying 0 elements in the request, the issue is solved, while then dynamic array behavior is used and 0 elements are then given back. Best regards Anton __________________________________________ From: Hill, Jeff [mailto:[email protected]] Hi Anton, Thanks for taking some time to report this issue. I will emulate the typical computer support personal and respond to a question with an escalating number of questions :-). Ø The Array has zero length (NORD=0) after boot. Then I get garbage as first Ø character while the number of elements is 128 in my case and this number Ø was requested. When specifying 0 at request I get args.count=0 as it should Ø with 3.14.12. o Is this issue repeatable when testing with a different client side code other than caget? If so, which ca client code is in use? o Is this issue repeatable when testing with multiple record types and or multiple device support modules? o You mention that the issue is related to NORD being zero just after booting the IOC. Does the problem persist or does it happen only once; if it doesn’t persist then what is the action that causes an improvement? For example, I could imagine some different scenarios where the behavior might improve the second time that a CA client attaches, in a particular client’s second subscription update, the first time that the record processes, or the second time that the record processes. o In what versions of EPICS does it fail, and in what versions does it work correctly; is it working correctly in 3.14.12? Thanks for your help. best regards, Jeff From: Mezger Anton Christian [mailto:[email protected]] Hi Jeff, The Array has zero length (NORD=0) after boot. Then I get garbage as first character while the number of elements is 128 in my case and this number was requested. When specifying 0 at request I get args.count=0 as it should with 3.14.12. Regards Anton __________________________________________ From: Hill, Jeff [mailto:[email protected]] Anton, As memory serves, a request for a zero length subscription will probably be rejected by an old version of the CA server. Jeff From: Mezger Anton Christian [mailto:[email protected]] Thank you Jeff, this confirms that I can set 0 in the ca_add_event_array. In any case of epics combinations (ioc, client) that would work properly at monitor receive. Thanks and best regards Anton __________________________________________ From: Hill, Jeff [mailto:[email protected]] Ø My question is: when specifying 0, how does that behave in older epics versions and channel Ø access gateways. Does it use then the maximum amount of elements ? When a channel connects the maximum number of elements is supplied by the server as a channel attribute. In newer versions of EPICS the current number of elements is returned with each subscription update. In older versions the maximum number of elements was always returned; when the current number of elements was less than the maximum number then any additional elements at the end were zero padded. Jeff From: [email protected] [mailto:[email protected]] On Behalf Of Mezger Anton Christian Hi all, When monitoring a non initialized char array with ca_add_event_array, one gets most of the time in the first element of the array. This only when the request uses ca_element_count(chid) which is non zero. When using the dynamic behavior by specifiying 0 elements, the received args.count correspond to the actual size of the array, including zero when not initialized. My question is: when specifying 0, how does that behave in older epics versions and channel access gateways. Does it use then the maximum amount of elements ? Anton __________________________________________ |