Timing Delay model in SIS tool

[daciccad]

Hi,
I am using SIS tool ( URL is embedded.eecs.berkeley.edu/Alumni/pchong/sis.html )
but I am unable to understand how the arrrival time and required time are calculated in the tool. I believe it should not be too difficult since SIS use very simple delay model. Can anyoue who are familiar with SIS tool to give me a little help ?
Your response is greatly appreciated.

Here is an example I tried.
The circuite is c17.blif
sis> read_blif c17.blif
sis> read_library sis_lib/mcnc.genlib
sis> read_library -a sis_lib/mcnc_latch.genlib
sis> map

sis> print_delay
... using library delay model
1GAT(0) : arrival=( 0.10 0.10) required=(-2.60 -2.60) slack=(-2.70 -2.70)
2GAT(1) : arrival=( 0.10 0.10) required=(-2.80 -2.80) slack=(-2.90 -2.90)
3GAT(2) : arrival=( 0.20 0.20) required=(-4.20 -4.20) slack=(-4.40 -4.40)
6GAT(3) : arrival=( 0.10 0.10) required=(-4.20 -4.20) slack=(-4.30 -4.30)
7GAT(4) : arrival=( 0.10 0.10) required=(-2.60 -2.60) slack=(-2.70 -2.70)
[289] : arrival=( 1.40 1.40) required=(-1.40 -1.40) slack=(-2.80 -2.80)
[286] : arrival=( 1.60 1.60) required=(-2.80 -2.80) slack=(-4.40 -4.40)
[293] : arrival=( 3.00 3.00) required=(-1.40 -1.40) slack=(-4.40 -4.40)
{22GAT(10)}: arrival=( 4.40 4.40) required=( 0.00 0.00) slack=(-4.40 -4.40)
[291] : arrival=( 2.80 2.80) required=(-1.40 -1.40) slack=(-4.20 -4.20)
{23GAT(9)}: arrival=( 4.40 4.40) required=( 0.00 0.00) slack=(-4.40 -4.40)
sis> constraints
A setting of UNSET means value not specified
Default settings:
input arrival=( 0.00 0.00 )
input drive=( 0.10 0.10 )
max input load=999.00
output load= 2.00
output required=( 0.00 0.00 )
wire_load slope= UNSET
Settings for input 1GAT(0): arrival=( UNSET UNSET ) drive=( UNSET UNSET ) max input load=UNSET
Settings for input 2GAT(1): arrival=( UNSET UNSET ) drive=( UNSET UNSET ) max input load=UNSET
Settings for input 3GAT(2): arrival=( UNSET UNSET ) drive=( UNSET UNSET ) max input load=UNSET
Settings for input 6GAT(3): arrival=( UNSET UNSET ) drive=( UNSET UNSET ) max input load=UNSET
Settings for input 7GAT(4): arrival=( UNSET UNSET ) drive=( UNSET UNSET ) max input load=UNSET
Settings for output {22GAT(10)}: load=UNSET required=( UNSET UNSET )
Settings for output {23GAT(9)}: load=UNSET required=( UNSET UNSET )