RE: ISAC: New IR 2109

Folks,

I just had a quick look over this IR, and see that it relates to the issues
of channels and interfaces that we've been canvassing in the VHDL-TC. The
submitter is looking to use protected types for a form of interprocess
communication (IPC). There are a whole bunch of different IPC mechanisms,
such as sempahores of different flavours and FIFOs queues, that embody both
abstract communication and synchronization. The synchronization aspects
involve waiting on one one or more conditions. This area has been well
explored and reported in the literature on concurrent programming and
operating systems.

The protected type mechanism that we included in VHDL-2000 was based on
Hoare monitors, but it only included the aspect of mutual exclusion on
method entry. Hoare monitors also involve declaring condition variables on
which a monitor can wait. While waiting, the caller relinquishes mutex,
allowing another monitor call to proceed. That call can affect state to make
the condition true, thus reenabling the suspended caller.

Assuming a lot of semantics, the submitter's semaphore type could be
expressed as

  type boolean_semaphore is protected
    procedure lock;
    procedure free;
  end protected boolean_semaphore;

  type boolean_semaphore is protected body
    variable available : boolean := true;
    procedure lock is
    begin
      while not available loop
        wait until available;
      available := false;
    end procedure lock;
    procedure free is
    begin
      available := true;
    end procedure free;
  end protected body boolean_semaphore;

This issue needs a lot of requirements analysis, especially as it relates to
transaction-level modeling. I suggest we punt it to the VHDL-TC
Requirements-SC.

Cheers,

PA

--
Dr. Peter J. Ashenden         peter@ashenden.com.au
Ashenden Designs Pty. Ltd.    www.ashenden.com.au
PO Box 640                    VoIP: sip://0871270078@sip.internode.on.net
Stirling, SA 5152             Phone (mobile):  +61 414 70 9106
Australia


> -----Original Message-----
> From: owner-isac@server.eda.org 
> [mailto:owner-isac@server.eda.org] On Behalf Of Chuck Swart
> Sent: Friday, 2 February 2007 9:40 AM
> To: isac@server.eda.org
> Subject: ISAC: New IR 2109
> 
> 
> This IR was just submitted. Let's discuss it at tonight's 
> meeting. The IR is also in the eda.org data base.
> 
> Chuck Swart
> 
> 
> 
> -- 
> This message has been scanned for viruses and
> dangerous content by MailScanner, and is
> believed to be clean.
> 
> 



-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.