Re: Packed Data Message Formats With Fixed-Length Strings

[Dirk Zimoch <dirk.zimoch@psi.ch>]

Hi Iain,

In StreamDevice you can use the variable MaxInput instead of a 
terminator if you have a fixed number of input bytes.

To give more advice I would need to see a message. 'Python struct format 
"128s12ii"' does not mean anything to me.

Dirk


On 08.11.2016 17:46, Iain Marcuson wrote:
> I am writing EPICS code to interface with a custom device.  The device protocol is fixed-length messages.  I can read and write the message parameters with Stream Device, and have done so successfully except for the fixed-length string, which I have had to bypass in assorted ways.
>
> The output command message has the Python struct format "ii128s12i".  The input message has the Python struct format "128s12ii".  The "12i" refers to 12 parameters, passed or returned.
>
> My two questions are:
>
> 1) How can I parse the fixed-length string?  The normal string-handling routines fail either because of terminator characters in the string or because the string is two long.
> 2) I handle the parameters by having a PV for each parameter, and a separate "group" of PVs for each command.  Is this best practice?
>
> Thank you,
>
> Iain Marcuson.