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IRSIM
There is quite a bit of on-line documentation for
irsim. Try man irsim for information on all
the commands that irsim supports. irsim is a
switch-level simulator, in the sense it models the circuit at the
level of transistors.
Commonly Used Commands
The most frequently used commands in irsim are those that set
the values of inputs and those that are used to view signals.
h node1 node2 ... |
set list of nodes to logic 1 (high) |
l node1 node2 ... |
set list of nodes to logic 0 (low) |
u node1 node2 ... |
set list of nodes to "X" (undefined) |
x node1 node2 ... |
stop setting the list of nodes |
d node1 node2 ... |
display current value of nodes |
ana node1 node2 ... |
display current value of nodes in waveform viewer |
clear |
clear waveform viewer display |
s |
run simulation for one step |
stepsize tm |
set step size to tm nanoseconds |
IMPORTANT. When you set a node high or low using the
h or l commands, the node keeps being set
to high or low (no matter what the circuit is trying to do to the
node!) until you use the x command to stop setting the
node.
Vectors
Since nodes typically are grouped into vectors, it is usually easier
to look at N-bit quantities as single vector entities. The
following commands can be used to define vectors and display them.
vector name node1 node2 ... |
define a new vector called name consisting of the list of nodes |
d name |
display a vector as an array of bits |
ana name |
add vector name to the waveform viewer |
set name value |
set the bits of vector name using the binary string value |
To set a vector to a hexadecimal number, use:
set name %xhexstring
For instance, you can now say: set Va %xff if
Va is an 8-bit vector instead of set Va
11111111. The prefix %x says that what follows is
a hex constant.
A useful shortcut to defining arrays as long vectors is to say:
vector name a.b[{31:0}]
Scripts
All the text commands shown above can be typed into a text file and
then read in at once. If you create a file called
foo.src, you can read it into irsim by
saying:
@ foo.src
foo.cmd, then simply saying:
foo
irsim will execute it. foo is treated as a new
irsim command that is defined by the contents of script foo.cmd.
Some useful commands for scripts are given below.
| comment |
A vertical pipe defines the rest of the line to be a comment.
Comments must be on separate lines (i.e. these are not like C++ style comments)
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assert name value |
This checks if name has value value. If this is
true, the command does nothing. Otherwise, the command prints an error
message. |
print text |
Echos text on the output. Useful to separate the outputs of
different major tests.
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