What is the meaning of this following sequence?

SystemVerilog
, ,
1 
 sequence iicByteSeq;
  @(posedge clk) 
  ##0 ( 1 [*1:$] ##0  iicBitSeq ) [*9] ;
 endsequence
2

In reply to Subhra Bera:


sequence iicBitSeq; 
     c ##1 b[*3]; endsequence 

 sequence iicByteSeq;
  @(posedge clk) 
  ##0 ( 1 [*1:$] ##0  iicBitSeq ) [*3] ;
 endsequence 
// Using 3 instead of $
// (1[*1:3] ##0  iicBitSeq) //is same as 
   (1[*1] ##0 iicBitSeq) or (1[*2] ##0 iicBitSeq)  or (1[*3] ##0 iicBitSeq)
// same as 
   (##0 iicBitSeq) or (##1 iicBitSeq)  or (##2 iicBitSeq)
// NOTE: 1'b1[*2] ##0 b // same as 
//       (1'b1 ##1 1'b1) ##0 b // same as 
//         ##1 b // 1'b1 ##0 b // same as b
##0 ( 1 [*1:$] ##0  iicBitSeq ) [*3] // same as 
(##0 iicBitSeq) or (##1 iicBitSeq)  or (##2 iicBitSeq)

Ben Cohen
http://www.systemverilog.us/ ben@systemverilog.us
For training, consulting, services: contact Home - My cvcblr

3

In reply to ben@SystemVerilog.us:
Then what is the meaning of this sequnce ?

 sequence nackSeq;
   ##1 1 [*1:$] ##0 $rose(scl) ##0 (iicByteCnt==0&&iicBitCnt==8&&sda&&scl) [*1:$] ##1 !scl;
 endsequence

If there is any rule to write this type of sequences then please refer it to me.

4

In reply to Subhra Bera:

If there is any rule to write this type of sequences then please refer it to me.

Yes, there is a rule: Define the requirements first in English.


 // The following sequence 
   ##1 1 [*1:$] ##0 $rose(scl) ##0 (iicByteCnt==0&&iicBitCnt==8&&sda&&scl) [*1:$] ##1 !scl;
// is of the form 
      ##1 1[*1:$] ##0 a ##0 b[*1:$] ##1 c;
// It is poorly written in form because 
   ##1 1[*1:$] ##0 a says that after 1 cycle you wait for an "a".  
// Better ways of expressing this include one of the following: 
   ##[1:$] a 
   ##1 a[->1]
// Thus, instead of    ##1 1[*1:$] ##0 a ##0 b[*1:$] ##1 c;
   ##[1:$] a ##0 b[*1:$] ##1 c; // 
in a consequent, the assertion can never fail.  e.g., isntead of: 
   w |->  ##[1:$] a ##0 b[*1:$] ##1 c; // CANNOT FAIL 
   w |->  ##1 a[->1] ##0 b[*1:$] ##1 c; // CAN FAIL 
   w |-> first_match( ##[1:$] a) ##0 b[*1:$] ##1 c;) Can FAIL, prefer the ##1 a[->1] instead

Ben Cohen
http://www.systemverilog.us/ ben@systemverilog.us
For training, consulting, services: contact Home - My cvcblr