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| <== Date ==> | <== Thread ==> |
|---|
| Subject: | Issue with Asyn+StreamDevice on a Raspi CM4 |
| From: | Florian Feldbauer via Tech-talk <tech-talk at aps.anl.gov> |
| To: | "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov> |
| Date: | Tue, 12 Jul 2022 09:44:01 +0200 |
Hey all, we have a small vacuum chamber to test our sensor modules after production.The 2 Pumps and 2 valves are controlled via a Raspberry Pi CM4 running linux-aarch64.
The Turbo pump and digital gauge are from Pfeiffer Vacuum and controlled via RS485.
I noticed some strange issue. I was able to read all parameters from those devices, but changing them fails.
To further investigate I attached a 2nd PC to the RS485 bus just listening and found the following:
epics> asynSetTraceIOMask rs485, 0, ASYN_TRACEIO_ESCAPE epics> asynSetTraceMask rs485, 0, ASYN_TRACEIO_DRIVER epics> dbpf SCATTERCHAMBER:VACUUM:TP:CtrlViaInt RS485 DBF_STRING: "RS485" 2022/07/12 09:25:52.084 /dev/ttyAMA0 write 17 0011006003002125\r2022/07/12 09:25:52.721930 rs485 SCATTERCHAMBER:VACUUM:TP:CtrlViaInt: No reply within 500 ms to "0011006003002125<0d>"2022/07/12 09:25:52.722 /dev/ttyAMA0 write 16 0010006002=?101\r 2022/07/12 09:25:52.762 /dev/ttyAMA0 read 16 0011006003002125 2022/07/12 09:25:52.766 /dev/ttyAMA0 read 1 \repics>
The 2nd PC received this:
Got 16 bytes: 0011006003002125 [30 30 31 31 30 30 36 30 30 33 30 30 32 31 32 35] Got 16 bytes: 0010006002=?101\r [30 30 31 30 30 30 36 30 30 32 3d 3f 31 30 31 0d] Got 17 bytes: 0011006003002125\r [30 30 31 31 30 30 36 30 30 33 30 30 32 31 32 35 0d]
As you can see, on the first message which was send from the IOC, the CR is missing.
I guess the issue is, that asyn tries to write all 17 bytes at once, but the tx buffer on the Raspberry Pi can only hold 16 byte, so the CR gets lost.
Is there a way to limit the number of bytes written in a single write call with asyn?
Luckily in this case the length of the telegrams is well known and I could simply use 2 OUT statements in my protocol file to work around this problem, but what if I want to control a device where the length depends on the payload data?
Cheers, Florian -- Ruhr-Universität Bochum AG der Experimentalphysik I Dr. Florian Feldbauer NB 2/131 / Fach 125 Universitätsstr. 150 D-44801 Bochum Office: NB 2/134 Phone: (+49)234 / 32-23563 Fax: (+49)234 / 32-14170 https://paluma.ruhr-uni-bochum.de