如何解决GENUS中未约束的异步复位端口问题？

xylimm

在sdc文件中用set_false_path约束异步复位端口rst，但GENUS仍然报告UNCONSTRAINED，使用以下三种写法结果都一样：

set_false_path -from [get_ports rst] -to [all_registers]
set_false_path -from [get_ports rst] -to [get_pins {scr_w/ds_reg[0]/aclr scr_r/ds_reg[0]/aclr}]
set_false_path -from [get_ports rst]

综合工具及版本：GENUS 191

调用check_timing_intent命令输出：

Timing exceptions with no effect

The following timing exceptions are not currently affecting timing in the      
design.  Either no paths in the design satisfy the exception's path            
specification, or all paths that satisfy the path specification also satisfy an
exception with a higher priority.  You can improve runtime and memory usage by  
removing these exceptions if they are not truly needed.  To see if there is a   
path in the design that satisfies the path specification for an exception, or   
to see what other exception is overriding an exception because of priority, use
the command:                                                                    
  report timing -paths [eval [::legacy::get_attribute paths <exception>]]

exception:async_fifo_W4_NE3/constraints.sdc_line_7

调用report timing -unconstrained -paths [eval [::legacy::get_attribute paths exception:async_fifo_W4_NE3/constraints.sdc_line_7]]命令输出：

Path 1: UNCONSTRAINED
     Startpoint: (R) rst
       Endpoint: (F) scr_w/ds_reg[0]/aclr

                   Capture    Launch  
      Drv Adjust:+       0        18  
                                      
       Data Path:-      52            

#-----------------------------------------------------------------------------------------------------
#    Timing Point      Flags    Arc    Edge      Cell        Fanout Load Trans Delay Arrival Instance
#                                                                   (fF)  (ps)  (ps)   (ps)  Location
#-----------------------------------------------------------------------------------------------------
  rst                  <<< (u) -       R     (arrival)            2  8.0    43     0      18    (-,-)
  scr_w/g1/z           (a,u)   in_0->z F     unmapped_not         4  8.0     0    34      52    (-,-)
  scr_w/ds_reg[0]/aclr <<<     -       F     unmapped_d_flop      4    -     -     0      52    (-,-)
#-----------------------------------------------------------------------------------------------------

(a) : Net has asynchronous load pins which are being considered ideal.
(u) : Net has unmapped pin(s).

GENUS中应该如何用set_false_path约束异步复位端口?

farmat913144

Usually Genus recognizes resets, no need to set false path. Try set_dont_touch_network

wmchpu

false path不就是不约束么

xylimm

farmat913144 发表于 2024-9-3 22:34
Usually Genus recognizes resets, no need to set false path. Try set_dont_touch_network

用了    set_dont_touch_network 结果还是一样的

xylimm

wmchpu 发表于 2024-9-4 16:39
false path不就是不约束么

set_false_path 是例外约束，也是一种约束，跟不约束是不同的
添加了例外约束，查看未约束路径应该就不报了

xylimm

现在的问题是用了set_false_path以后用report timing -unconstrained检查未约束路径还能看到
应该是set_false_path没有起作用，所以应该怎么用set_false_path？或者应该用哪个命令？

xylimm

未约束路径只报1个是因为默认最多报1个，添加选项 -nworst 20 就最多报20个了

farmat913144

Do you use timing library containing FFs with async reset?

xylimm

farmat913144 发表于 2024-9-12 19:33
Do you use timing library containing FFs with async reset?

有的

xylimm

farmat913144 发表于 2024-9-3 22:34
Usually Genus recognizes resets, no need to set false path. Try set_dont_touch_network

GENUS手册里有写异步复位会被设置ideal_network属性，Usually Genus recognizes resets 指的是这个么？ideal_network属性的作用应该是忽略网络延迟吧？还会自动设置false path么？确实删掉set_false_path就不报Timing exceptions with no effect了，但是report timing -unconstrained -from [get_ports rst]还是会报UNCONSTRAINED。