Modbus & asynManager::queueLockPort queueRequest failed: port not connected

[Keara Louise Soloway via Tech-talk <tech-talk at aps.anl.gov>]

Greetings all,

I am having problems communicating with an Automation Direct BRX PLC. The problems are not consistently reproducible -- IOC starts without any error at all about 1 in 5 times. The errors only happen when starting the IOC, never when it's already running normally.

The IOC application uses:

EPICS base 7.0.2

alive R1-1-1

asyn R4-40

calc R3-7-3

modbus R3-0

sscan R2-11-3

Here are the errors and some context from the ioc shell:

## Register all support components

dbLoadDatabase("../../dbd/heatedprintbed.dbd")

heatedprintbed_registerRecordDeviceDriver(pdbbase)

< errordemo.cmd

drvAsynIPPortConfigure("IP_PORT", "192.168.182.136:502",0,0,1)

modbusInterposeConfig("IP_PORT",0,5000,0)

drvModbusAsynConfigure("MI_READ", "IP_PORT", 255, 2, 549, 11, 0, 250, "BRX")

drvModbusAsynConfigure("MC_READ",  "IP_PORT", 255, 1, 1999, 5, 0, 250, "BRX")

drvModbusAsynConfigure("MC_WRITE", "IP_PORT", 255, 5, 1999, 5, 0, 250, "BRX")

2021/05/20 15:58:50.578 drvModbusAsyn::doModbusIO port MC_WRITE error calling writeRead, error=asynManager::queueLockPort queueRequest failed: port IP_PORT not connected, nwrite=0/6, nread=0

## Load record instances

dbLoadTemplate("../../db/errordemo.substitutions")

iocInit

Starting iocInit

############################################################################

## EPICS R7.0.2

## EPICS Base built Apr  5 2019

############################################################################

2021/05/20 15:58:50.828 drvModbusAsyn::doModbusIO port MI_READ error calling writeRead, error=asynManager::queueLockPort queueRequest failed: port IP_PORT not connected, nwrite=0/6, nread=0

2021/05/20 15:58:50.828 drvModbusAsyn::doModbusIO port MC_READ error calling writeRead, error=asynManager::queueLockPort queueRequest failed: port IP_PORT not connected, nwrite=0/6, nread=0

iocRun: All initialization complete

## Start any sequence programs

#seq sncxxx,"user=kls286"

epics> 2021/05/20 16:01:25.169 drvModbusAsyn::doModbusIO port MI_READ writeRead status back to normal having had 124 errors, nwrite=6/6, nread=4

2021/05/20 16:01:25.175 drvModbusAsyn::doModbusIO port MC_READ writeRead status back to normal having had 124 errors, nwrite=6/6, nread=3

After a few minutes (variable, but usually less than 10), all of the read-only modbus ports put out a "back to normal" message like the one above. The claim of "back to normal" does indeed seem to be true -- all PVs reading from these ports do so as intended. 

The write-only modbus ports also go back to normal as soon as I do a dbpf to any of the PVs that will write to the port. Like so:

epics> dbpf demoButton:write 1
DBF_STRING:         "Pushed"

epics> 2021/05/20 16:04:37.323 drvModbusAsyn::doModbusIO port MC_WRITE writeRead status back to normal having had 1 errors, nwrite=6/6, nread=5

Let me know if I can provide any additional details. 

Thanks,

K. Soloway