Increate Quality Bound with JG

2015/8/18
Increate Quality Bound with JG
– CHI Protocol Verification Practice
Yan Guofeng
Verification Dept.
Formal and Automation Verification Group
Aug 2015
HUAWEI TECHNOLOGIES CO., LTD.
www.huawei.com
Agenda
Formal verification environment
Top One problem: explored
how to solve the “explored “
bound proof
summary
Closing
HUAWEI TECHNOLOGIES CO., LTD.
Page 2
Our roadmap
Milestone
Grown up
Start
•International team
•Formal export
•Formal platform
•Formal flow
•International team
•CPU/DSP/Device chipset
• JG
•Bug-hunting/sign-off
•Simulation guys/formal juniors
•CPU
•IEV/JG
Now
HUAWEI TECHNOLOGIES CO., LTD.
Page 3
CHI bridge Verification Env
HUAWEI TECHNOLOGIES CO., LTD.
Page 4
Agenda
Formal verification environment
Top One problem: explored
how to solve the “explored “
bound proof
summary
Closing
HUAWEI TECHNOLOGIES CO., LTD.
Page 5
Trace and engine
Z
K
N
M
All engines prove in parallel !
Ht
I
B
L
HUAWEI TECHNOLOGIES CO., LTD.
Page 6
Top One Problem - explored
Too complexity
to prove
Assumption
a property not yet computed
a property under computation
false : CEX found (assert), or proven unreachable (cover )
true : proven (assert), or an example found (cover)
time-out (“undetermined”)
error in formal analysis, by improper assumptions conflicts
with each other or with design
HUAWEI TECHNOLOGIES CO., LTD.
Page 7
Agenda
Formal verification environment
Top One problem: explored
how to solve the “explored “
bound proof
summary
Closing
HUAWEI TECHNOLOGIES CO., LTD.
Page 8
Engine select
HUAWEI TECHNOLOGIES CO., LTD.
Page 9
Coding style - ND
assume property ( @(posedge clk) $stable(B) );
assume property ( @(posedge clk) 0<=B && B<32 );
always @(posedge clk or negedge rst_n) begin
if(!rst_n) begin
A_sb <= 1’b0;
end
else begin
A_sb <= A[B];
end
assert property ( @(posedge clk) A_out[B] == A_sb );
HUAWEI TECHNOLOGIES CO., LTD.
always @(posedge clk or negedge rst_n) begin
if(!rst_n) begin
A_sb <= 32’b0;
end
else begin
A_sb <= A;
end
assert property ( @(posedge clk) A_out == A_sb );
Page 10
Data integrity check

scenario
00000000000000000110011

DUT
00000000000000000110011
DUT
00000000000000000011000
Formal check
Formal decides when to inject these two bits
00000000000000000011000
HUAWEI TECHNOLOGIES CO., LTD.
Page 11
Error cases covered
Loss:
0*0110*0
0
0
1
1
0
0
0
1
1 1 0
0
0
1
0
0
0
0
0*010*0
Duplication:
0*0110*0
0
0
0
0*01110*0
Switch:
0*0110*0
HUAWEI TECHNOLOGIES CO., LTD.
1
0
0
0
0*01010*0
Page 12
DI and Proof accelerator
Proof Accelerator Scoreboard_2
JasperGold PA DI assertion proven
HUAWEI TECHNOLOGIES CO., LTD.
Page 13
Initial value abstract(IVA)
Relationship between link layer and protocol layer
cover aa init with reset value
cover aa init with link run state
HUAWEI TECHNOLOGIES CO., LTD.
Page 14
Over-constraints
Constrains
DUT
entry1
entry1
entry2
entry3
entry2
VIP
checkers
….……
….……
Over-constraints
entry n
before over-constraint
after over-constraint
HUAWEI TECHNOLOGIES CO., LTD.
Page 15
Agenda
Formal verification environment
Top One problem: explored
how to solve the “explored “
bound proof
summary
Closing
HUAWEI TECHNOLOGIES CO., LTD.
Page 16
bound proof
HUAWEI TECHNOLOGIES CO., LTD.
Page 17
Bound-proof report analysis
HUAWEI TECHNOLOGIES CO., LTD.
Page 18
Bound-proof tips

Critical feature assertion must be proven.

Prove as deeper as we can


Bound proof is the compromise between effort and quality

Example

Pg table : 32 enter / IVA

Local dev rd/wr fifo: visualize as initial value
Run enough bug hunting with bounded proof case
HUAWEI TECHNOLOGIES CO., LTD.
Page 19
Agenda
Formal verification environment
Top One problem: explored
how to solve the “explored “
bound proof
summary
Closing
HUAWEI TECHNOLOGIES CO., LTD.
Page 20
Summary


Result

Several env/RTL problems are found

Simulation doesn’t find any bug after formal
Next step

Designer split the design in the next version to reduce complexity

It is expected that JG can integrate dead-end debug capability
(2015.06)

It is expected that JG continue to improve the proof-core coverage
metrics.
HUAWEI TECHNOLOGIES CO., LTD.
Page 21
Thank you
www.huawei.com