transaction vs event

[canadianJaouk]

Does anyone know what the difference between <signal>'event and
<signal>'transaction is? Anyone has a precise definition of these
keywords?

Thanks
-Jake

 

[Jonathan Bromley]

On 3 Nov 2006 11:31:10 -0800, "canadianJaouk"
<jaouque@yahoo.ca> wrote:

Does anyone know what the difference between <signal>'event and
signal>'transaction is? Anyone has a precise definition of these

<sig>'event is a boolean value that is TRUE in a delta cycle when
<sig> has just changed, and FALSE at other times. You can test
'event in an IF statement. Take, for example, the not-very-pretty
traditional form of clocked process:

process(clk, rst)
begin
if rst='1' then
-- do reset actions
elsif clk='1' and clk'event then
-- clk has just changed to '1', and
-- that change triggered the process
-- so do clocked actions

<sig>'transaction allows you to check whether some assignment was
made to the signal, even if that assignment didn't change the
signal's value. <sig>'transaction is a completely new signal,
of type BIT, that toggles from '0' to '1' or back again in each
delta cycle when one or more assignment is made to <sig>.
This is occasionally useful if you have a data structure representing
a transaction, and you would like to detect when someone puts
a new value on that data structure - even if it's the same as
the existing value. Because it's a new signal in its own right,
you can use it in a sensitivity list...

wait on thing'transaction;
-- someone has written to "thing"
-- so we need to process the new value

Fairly obviously, 'transaction is not synthesisable. 'event is
synthesisable in a few special cases.
--
Jonathan Bromley, Consultant

DOULOS - Developing Design Know-how
VHDL * Verilog * SystemC * e * Perl * Tcl/Tk * Project Services

Doulos Ltd., 22 Market Place, Ringwood, BH24 1AW, UK
jonathan.bromley@MYCOMPANY.com
http://www.MYCOMPANY.com

The contents of this message may contain personal views which
are not the views of Doulos Ltd., unless specifically stated.

 

[canadianJaouk]

Thanks very much. That's exactly what i was looking for. I have
further questions however.

I have seen the 'transaction used in a statement that looks like this:

wait on <sig>'transaction until <some condition>

what does the until <some condition> means in this context?

On Nov 3, 4:54 pm, Jonathan Bromley <jonathan.brom...@MYCOMPANY.com>
wrote:

On 3 Nov 2006 11:31:10 -0800, "canadianJaouk"

jaou...@yahoo.ca> wrote:
Does anyone know what the difference between <signal>'eventand
signal>'transactionis? Anyone has a precise definition of these<sig>'eventis a boolean value that is TRUE in a delta cycle when
sig> has just changed, and FALSE at other times. You can test
'eventin an IF statement. Take, for example, the not-very-pretty
traditional form of clocked process:

process(clk, rst)
begin
if rst='1' then
-- do reset actions
elsif clk='1' and clk'eventthen
-- clk has just changed to '1', and
-- that change triggered the process
-- so do clocked actions

sig>'transactionallows you to check whether some assignment was
made to the signal, even if that assignment didn't change the
signal's value. <sig>'transactionis a completely new signal,
of type BIT, that toggles from '0' to '1' or back again in each
delta cycle when one or more assignment is made to <sig>.
This is occasionally useful if you have a data structure representing
atransaction, and you would like to detect when someone puts
a new value on that data structure - even if it's the same as
the existing value. Because it's a new signal in its own right,
you can use it in a sensitivity list...

wait on thing'transaction;
-- someone has written to "thing"
-- so we need to process the new value

Fairly obviously, 'transactionis not synthesisable. 'eventis
synthesisable in a few special cases.
--
Jonathan Bromley, Consultant

DOULOS - Developing Design Know-how
VHDL * Verilog * SystemC * e * Perl * Tcl/Tk * Project Services

Doulos Ltd., 22 Market Place, Ringwood, BH24 1AW, UK
jonathan.brom...@MYCOMPANY.comhttp://www.MYCOMPANY.com

The contents of this message may contain personal views which
are not the views of Doulos Ltd., unless specifically stated.

 

[Jim Lewis]

canadianJaouk wrote:

I have seen the 'transaction used in a statement that looks like this:

wait on <sig>'transaction until <some condition

what does the until <some condition> means in this context?

Whenever the signal "<sig>'transaction" changes, "<some condition>"
is evaluated and when "<some condition>" is true, the
wait statement wakes up.


--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jim Lewis
Director of Training mailto:Jim@SynthWorks.com
SynthWorks Design Inc. http://www.SynthWorks.com
1-503-590-4787

Expert VHDL Training for Hardware Design and Verification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

[canadianJaouk]

Here is a transcript of the evolution of a signal through time. The
value clearly changes, but the signal's transaction signal is always ?
Should it not go to 1 as soon as the signal value changes? Any ideas?

time delta value value'transaction
0 +0 -1e+308 ?
0 +2 -1e+100 ?
0 +3 400 ?
10 +4 -1e+100 ?
10 +5 2.4 ?

On Nov 15, 9:17 pm, Jim Lewis <J...@SynthWorks.com> wrote:

canadianJaouk wrote:
I have seen the 'transactionused in a statement that looks like this:

wait on <sig>'transactionuntil <some condition

what does the until <some condition> means in this context?Whenever the signal "<sig>'transaction" changes, "<some condition>"
is evaluated and when "<some condition>" is true, the
wait statement wakes up.

--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jim Lewis
Director of Training mailto:J...@SynthWorks.com
SynthWorks Design Inc. http://www.SynthWorks.com
1-503-590-4787

ExpertVHDLTraining for Hardware Design and Verification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~