Chapter 7
IOC Initialization

 7.1 Overview - Environments requiring a main program
 7.2 Overview - vxWorks
 7.3 Overview - RTEMS
 7.4 IOC Initialization
  7.4.1 Configure Main Thread
  7.4.2 General Purpose Modules
  7.4.3 Channel Access Links
  7.4.4 Driver Support
  7.4.5 Record Support
  7.4.6 Device Support
  7.4.7 Database Records
  7.4.8 Device Support again
  7.4.9 Scanning and Access Security
  7.4.10 Initial Processing
  7.4.11 Channel Access Server
  7.4.12 Enable Record Processing
  7.4.13 Enable CA Server
 7.5 Pausing an IOC
 7.6 Changing iocCore fixed limits
  7.6.1 callbackSetQueueSize
  7.6.2 dbPvdTableSize
  7.6.3 scanOnceSetQueueSize
  7.6.4 errlogInit or errlogInit2
 7.7 initHooks
 7.8 Environment Variables
 7.9 Initialize Logging

7.1 Overview - Environments requiring a main program

If a main program is required (most likely on all environments except vxWorks and RTEMS), then initialization is performed by statements residing in startup scripts which are executed by iocsh. An example main program is:

int main(int argc,char argv[]) 
    if (argc >= 2) { 
    return 0; 

The first call to iocsh executes commands from the startup script filename which must be passed as an argument to the program. The second call to iocsh with a NULL argument puts iocsh into interactive mode. This allows the user to issue the commands described in the chapter on “IOC Test Facilities” as well as some additional commands like help.

The command file passed is usually called the startup script, and contains statements like these:

  < envPaths
  cd ${TOP}
  dbLoadDatabase "dbd/appname.dbd"
  appname_registerRecordDeviceDriver pdbbase
  dbLoadRecords "db/file.db", "macro=value"
  cd ${TOP}/iocBoot/${IOC}

The envPaths file is automatically generated in the IOC’s boot directory and defines several environment variables that are useful later in the startup script. The definitions shown below are always provided; additional entries will be created for each support module referenced in the application’s configure/RELEASE file:


7.2 Overview - vxWorks

After vxWorks is loaded at IOC boot time, commands like the following, normally placed in the vxWorks startup script, are issued to load and initialize the application code:

  # Many vxWorks board support packages need the following:
  #cd <full path to IOC boot directory>
  < cdCommands
  cd topbin
  ld 0,0, "appname.munch"
  cd top
  dbLoadDatabase "dbd/appname.dbd"
  appname_registerRecordDeviceDriver pdbbase
  dbLoadRecords "db/file.db", "macro=value"
  cd startup

The cdCommands script is automatically generated in the IOC boot directory and defines several vxWorks global variables that allow cd commands to various locations, and also sets several environment variables. The definitions shown below are always provided; additional entries will be created for each support module referenced in the application’s configure/RELEASE file:

  startup = "/path/to/application/iocBoot/iocname"
  putenv "ARCH=vxWorks-68040"
  putenv "IOC=iocname"
  top = "/path/to/application"
  putenv "TOP=/path/to/application"
  topbin = "/path/to/application/bin/vxWorks-68040"
  epics_base = "/path/to/base"
  putenv "EPICS_BASE=/path/to/base"
  epics_basebin = "/path/to/base/bin/vxWorks-68040"

The ld command in the startup script loads EPICS core, the record, device and driver support the IOC needs, and any application specific modules that have been linked into it.

dbLoadDatabase loads database definition files describing the record/device/driver support used by the application..

dbLoadRecords loads record instance definitions.

iocInit initializes the various epics components and starts the IOC running.

7.3 Overview - RTEMS

RTEMS applications can start up in many different ways depending on the board-support package for a particular piece of hardware. Systems which use the Cexp package can be treated much like vxWorks. Other systems first read initialization parameters from non-volatile memory or from a BOOTP/DHCP server. The exact mechanism depends upon the BSP. TFTP or NFS filesystems are then mounted and the IOC shell is used to read commands from a startup script. The location of this startup script is specified by a initialization parameter. This script is often similar or identical to the one used with vxWorks. The RTEMS startup code calls

epicsRtemsInitPreSetBootConfigFromNVRAM(struct rtems_bsdnet_config ⋆);

just before setting the initialization parameters from non-volatile memory, and

epicsRtemsInitPostSetBootConfigFromNVRAM(struct rtems_bsdnet_config ⋆);

just after setting the initialization parameters. An application may provide either or both of these routines to perform any custom initialization required. These function prototypes and some useful external variable declarations can be found in the header file epicsRtemsInitHooks.h

7.4 IOC Initialization

An IOC is normally started with the iocInit command as shown in the startup scripts above, which is actually implemented in two distinct parts. The first part can be run separately as the iocBuild command, which puts the IOC into a quiescent state without allowing the various internal threads it starts to actually run. From this state the second command iocRun can be used to bring it online very quickly. A running IOC can be quiesced using the iocPause command, which freezes all internal operations; at this point the iocRun command can restart it from where it left off, or the IOC can be shut down (exit the program, or reboot on vxWorks/RTEMS). Most device support and drivers have not yet been written with the possibility of pausing an IOC in mind though, so this feature may not be safe to use on an IOC which talks to external devices or software.

IOC initialization using the iocBuild and iocRun commands then consists of the following steps:

7.4.1 Configure Main Thread

Providing the IOC has not already been initialized, initHookAtIocBuild is announced first.

The main thread’s epicsThreadIsOkToBlock flag is set, the message “Starting iocInit” is logged and epicsSignalInstallSigHupIgnore called, which on Unix architectures prevents the process from shutting down if it later receives a HUP signal.

At this point, initHookAtBeginning is announced.

7.4.2 General Purpose Modules

Calls coreRelese which prints a message showing which version of iocCore is being run.

Calls taskwdInit to start the task watchdog. This accepts requests to watch other tasks. It runs periodically and checks to see if any of the tasks is suspended. If so it issues an error message, and can also invoke callback routines registered by the task itself or by other software that is interested in the state of the IOC. See ”Task Watchdog” on page 560 for details.

Starts the general purpose callback tasks by calling callbackInit. Three tasks are started at different scheduling priorities.

initHookAfterCallbackInit is announced.

7.4.3 Channel Access Links

Calls dbCaLinkInit. The initializes the module that handles database channel access links, but does not allow its task to run yet.

initHookAfterCaLinkInit is announced.

7.4.4 Driver Support

initDrvSup locates each device driver entry table and calls the init routine of each driver.

initHookAfterInitDrvSup is announced.

7.4.5 Record Support

initRecSup locates each record support entry table and calls the init routine for each record type.

initHookAfterInitRecSup is announced.

7.4.6 Device Support

initDevSup locates each device support entry table and calls its init routine specifying that this is the initial call.

initHookAfterInitDevSup is announced.

7.4.7 Database Records

initDatabase is called which makes three passes over the database performing the following functions:

  1. Initializes the fields RSET, RDES, MLOK, MLIS, PACT and DSET for each record.

    Calls record support’s init_record (first pass).

  2. Convert each PV_LINK into a DB_LINK or CA_LINK

    Calls any extended device support’s add_record routine.

  3. Calls record support’s init_record (second pass).

Finally it registers an epicsAtExit routine to shut down the database when the IOC application exits.

Next dbLockInitRecords is called to create the lock sets.

Then dbBkptInit is run to initialize the database debugging module.

initHookAfterInitDatabase is announced.

7.4.8 Device Support again

initDevSup locates each device support entry table and calls its init routine specifying that this is the final call.

initHookAfterFinishDevSup is announced.

7.4.9 Scanning and Access Security

The periodic, event, and I/O event scanners are initialized by calling scanInit, but the scan threads created are not allowed to process any records yet.

A call to asInit initailizes access security. If this reports failure, the IOC initialization is aborted.

dbProcessNotifyInit initializes support for process notification.

After a short delay to allow settling, initHookAfterScanInit is announced.

7.4.10 Initial Processing

initialProcess processes all records that have PINI set to YES.

initHookAfterInitialProcess is announced.

7.4.11 Channel Access Server

The Channel Access server is started by calling rsrv_init, but its tasks are not allowed to run so it does not announce its presence to the network yet.

initHookAfterCaServerInit is announced.

At this point, the IOC has been fully initialized but is still quiescent. initHookAfterIocBuilt is announced. If started using iocBuild this command completes here.

7.4.12 Enable Record Processing

If the iocRun command is used to bring the IOC out of its initial quiescent state, it starts here.

initHookAtIocRun is announced.

The routines scanRun and dbCaRun are called in turn to enable their associated tasks and set the global variable interruptAccept to TRUE (this now happens inside scanRun). Until this is set all I/O interrupts should have been ignored.

initHookAfterDatabaseRunning is announced. If the iocRun command (or iocInit) is being executed for the first time, initHookAfterInterruptAccept is announced.

7.4.13 Enable CA Server

The Channel Access server tasks are allowed to run by calling rsrv_run.

initHookAfterCaServerRunning is announced. If the IOC is starting for the first time, initHookAtEnd is announced.

A command completion message is logged, and initHookAfterIocRunning is announced.

7.5 Pausing an IOC

The command iocPause brings a running IOC to a quiescent state with all record processing frozen (other than possibly the completion of asynchronous I/O operations). A paused IOC may be able to be restarted using the iocRun command, but whether it will fully recover or not can depend on how long it has been quiescent and the status of any device drivers which have been running. The operations which make up the pause operation are as follows:

  1. initHookAtIocPause is announced.
  2. The Channel Access Server tasks are paused by calling rsrv_pause
  3. initHookAfterCaServerPaused is announced.
  4. The routines dbCaPause and scanPause are called to pause their associated tasks and set the global variable interruptAccept to FALSE.
  5. initHookAfterDatabasePaused is announced.
  6. After logging a pause message, initHookAfterIocPaused is announced.

7.6 Changing iocCore fixed limits

The following commands can be issued after iocCore is loaded to change iocCore fixed limits. The commands should be given before any dbLoadDatabase commands.

  errlogInit2(buffersize, maxMessageSize)

7.6.1 callbackSetQueueSize

Requests for the general putpose callback tasks are placed in a ring buffer. This command can be used to set the size for the ring buffers. The default is 2000. A message is issued when a ring buffer overflows. It should rarely be necessary to override this default. Normally the ring buffer overflow messages appear when a callback task fails.

7.6.2 dbPvdTableSize

Record instance names are stored in a process variable directory, which is a hash table. The default number of hash entries is 512. dbPvdTableSize can be called to change the size. It must be called before any dbLoad commands and must be a power of 2 between 256 and 65536. If an IOC contains very large databases (several thousand records) then a larger hash table size speeds up searches for records.

7.6.3 scanOnceSetQueueSize

scanOnce requests are placed in a ring buffer. This command can be used to set the size for the ring buffer. The default is 1000. It should rarely be necessary to override this default. Normally the ring buffer overflow messages appear when the scanOnce task fails.

7.6.4 errlogInit or errlogInit2

These commands can increase (but not decrease) the default buffer and maximum message sizes for the errlog message queue. The default buffer size is 1280 bytes, the maximum message size defaults to 256 bytes.

7.7 initHooks

The inithooks facility allows application functions to be called at various states during ioc initialization. The states are defined in initHooks.h, which contains the following definitions:

typedef enum { 
    initHookAtIocBuild = 0,         /⋆ Start of iocBuild/iocInit commands ⋆/ 
    initHookAfterIocBuilt,          /⋆ End of iocBuild command ⋆/ 
    initHookAtIocRun,               /⋆ Start of iocRun command ⋆/ 
    initHookAfterIocRunning,        /⋆ End of iocRun/iocInit commands ⋆/ 
    initHookAtIocPause,             /⋆ Start of iocPause command ⋆/ 
    initHookAfterIocPaused,         /⋆ End of iocPause command ⋆/ 
/⋆ Deprecated states, provided for backwards compatibility. 
  These states are announced at the same point they were before, 
  but will not be repeated if the IOC gets paused and restarted. 
    initHookAfterInterruptAccept,   /⋆ After initHookAfterDatabaseRunning ⋆/ 
    initHookAtEnd,                  /⋆ Before initHookAfterIocRunning ⋆/ 
typedef void (⋆initHookFunction)(initHookState state); 
int initHookRegister(initHookFunction func); 
const char initHookName(int state);

Any functions that are registered before iocInit reaches the desired state will be called when it reaches that state. The initHookName function returns a static string representation of the state passed into it which is intended for printing. The following skeleton code shows how to use this facility:

static initHookFunction myHookFunction; 
int myHookInit(void) 
static void myHookFunction(initHookState state) 
  switch(state) { 
    case initHookAfterInitRecSup: 
    case initHookAfterInterruptAccept: 

An arbitrary number of functions can be registered.

7.8 Environment Variables

Various environment variables are used by iocCore:


For an explanation of the EPICS_CA_... and EPICS_CAS_... variables see the EPICS Channel Access Reference Manual. For an explaination of the EPICS_IOC_LOG_... variables see ”iocLogClient” on page 445 of this manual. EPICS_TS_NTP_INET is used only on vxWorks and RTEMS, where it sets the address of the Network Time Protocol server. If it is not defined the IOC uses the boot server as its NTP server.

These variables can be set through iocsh via the epicsEnvSet command, or on vxWorks using putenv. For example:


All epicsEnvSet commands should be issued after iocCore is loaded and before any dbLoad commands.

The following commands can be issued to iocsh:

epicsPrtEnvParams – This shows just the environment variables used by iocCore.

epicsEnvShow – This shows all environment variables on your system.

7.9 Initialize Logging

Initialize the logging system. See the chapter on “IOC Error Logging” for details. The following can be used to direct the log client to use a specific host log server.

  epicsEnvSet("EPICS_IOC_LOG_PORT", "<port>")
  epicsEnvSet("EPICS_IOC_LOG_INET", "<inet addr>")

These command must be given immediately after iocCore is loaded.

To start logging you must issue the command: