dynamic loading tasks and address space

Till Straumann strauman at slac.stanford.edu
Mon Nov 14 20:16:17 UTC 2005

Just a 'reminder' for the record

RTEMS 'events' and 'notepads' are limited resources also sometimes
used by 'semi-kernel' code (e.g., networking uses some events, NFS some
more, EPICS uses a notepad etc.). Usually, these are allocated an arbitrary
number from the middle or end of the available range.

a) make sure the notepad you use isn't in use
b) by 'convention', using low numbers for applications should be ok.

IMO it would be a good idea to
  a) setup a wiki-page to document use of events + notepads etc. by 
      software packages/'libraries'
  b) maybe come up with a dynamic allocation scheme (like for device 


Stanley Jobson wrote:

>>>question: what about this file? each instance of the task mentioned
>>>above would need its own copy (especially of the global (static)
>>>variables), right?
>>no. There is a single copy of the program text and all non-automatic 
>>Hence, if your code needs 'global' variables you must make it 
>>'re-entrant' first.
>>E.g., by putting all globals into a 'struct', malloc'ing memory for that 
>>at task initialization and passing a pointer to all routines that need 
>>to access the
>>global data. Instead of explicitely passing a pointer you can use RTEMS 
>>such as notepads or task variables [avoid task vars if possible - they 
>>add to
>>the context switching overhead] -- (RTM).
>thx for this detailed info - finally i found a way to solve my prob and i
>exactly did as u said: the code is loaded only once - a task must be
>reentrant, which will be impl. using rtems notepad ...

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