asyn C++ interface (asynPortDriver) usage demo.

It uses ioc type template.

PV names: echo, echo_rbv You can start ioc shell in terminal A, camonitor echo echo_rbv in terminal B, caput echo <num> in terminal C, and check output in terminal A B.

Only support C++14 compatible compilers

How to add PV

Suppose I want to add longin/longout pv echo/echo_rbv. (rbv: reedback value)

1. Define binding

Define param string to bind with pv(s) (e.g. DUMMY_ECHO) in your heart or documentaion. We will use it later

In normal epics ioc, we will bind DTYP, device dbd, c struct, and INP/OUT field map to function handler or value.

In asyn drvier, we will bind param string,param value in c source and its header

2. Define Record

Define record (see 'dummyApp/Db/dummy.db'), we should set string asyn(...DUMMY_ECHO) in INP/OUT field. In DTYP we use asynInt32. We can use asynXXXX which is defined in its documentation.

After this step, we can map param string to pv(s).

Note that we set I/O Intr in input (longin,ai,bi,stringin,etc) type SCAN field.

3. Inherit asynPortDriver

We should define our class and override asynPortDriver virtual functions, it has doxygen documentation.

4. Define Value

Define value in c++ sources (see sources under 'dummyApp/src/'), we need to define int type index for our param value.

And in constructor, we use createParam(<param string>, <param type>, <param value index>) to bind record's param string with our internal param value, the param vlaue index will be initialized. Then we can use setXXXParam,getXXXParam with param value index to read/write our internal param value.

param value is variable which will be exposed to IOC.

5. Define Handler

For output (longout,ao,bo,stringout,etc) type PV, we may need to write a handler. asynPortDriver gives us interface like writeInt32. These functions will only be called when one record is processing. These functions will give us param value index (we defined and initialized in step 4) to indicate which record is processing.

Do not forget to call callParamCallbacks(), it help us deal with input Record process with SCAN I/O Intr.

diagram:

caput call -> <param_string> -> asynPortDriver interface -> <param_value_index> -> our handler -> <param_value>

6. Setup ioc shell

We can define ioc shell function. Then in cmd file we can call this ioc shell function to create our driver

Tips

• Do not forget set environment variables to make EPICS ugly build system find base and asyn.
• Do not forget adding db files into Makefile