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====== tessent occ ======

{{:edastudy:tessent:pasted:20240221-092547.png?nolink}}


===== - operation mode =====

==== - function mode ====

functional mode (test_mode = 0) that enables the fast clock gater to supply a fast clock to the design.

==== - shift mode ====
shift mode (scan_en = 1) that uses the slow_clock to load and unload the  scan chains, including the condition bits in ShiftReg.

==== - shift only mode ====
Shift-only mode <color #ed1c24>disables the OCC (test_mode = 0)</color> and <color #ed1c24>activates shift (scan_en = 1)</color>. It enables  the slow clock clock gater to use the slow clock path for shift, and it enables bypass shift.

这个信号默认需要连接到 DFT信号ext_ltest_en 

==== - slow capture mode ====

slow capture mode (fast_capture_mode = 0) that uses the slow_clock to capture data into the scan cells and to shift the condition bits in ShiftReg.

==== - fast capture mode ====

fast capture mode (fast_capture_mode = 1) that uses the fast_clock to capture data into the scan cells and to shift the condition bits in ShiftReg.

==== - kill clock mode ====

kill clock mode (kill_clock_en = 1) that enables you to block propagation of fast_clock input to clock_out output. Asserting the kill_clock_en signal is effective in the two operating modes when the OCC is not active:



===== - 结构伪代码 =====

<code verilog>

  
   clock_mux21 tessent_persistent_cell_inject_tck_mux (
     .A0                                     ( slow_clock_buf_out               ),
     .A1                                     ( ijtag_tck                        ),
     .S0                                     ( inject_tck                       ),
     .Y                                      ( slow_clock_tck_injected          )
   );


   cgand tessent_persistent_cell_cgc_fast_clock (
     .CK                                     ( fast_clock_buf_out               ),
     .FE                                     ( fast_clock_en                    ),
     .TE                                     ( fast_clock_en                    ),
     .GCK                                    ( fast_clock_gated                 )
   );
  
   cgand tessent_persistent_cell_cgc_slow_clock (
     .CK                                     ( slow_clock_tck_injected          ),
     .FE                                     ( slow_clock_en                    ),
     .TE                                     ( slow_clock_en                    ),
     .GCK                                    ( slow_clock_gated                 )
   );
 
   clock_mux21 tessent_persistent_cell_clock_out_mux  (
     .A0                                     ( fast_clock_gated                 ),
     .A1                                     ( slow_clock_gated                 ),
     .S0                                     ( clock_mux_select                 ),
     .Y                                      ( clock_out                        )
   );

 
   assign kill_clock_en_gated = kill_clock_en & ~test_mode;
   assign fast_clock_en    = ((ShiftReg_SCAN_OUT & fast_capture_mode & (SCAN_EN_inv_sync || active_upstream_parent_occ)) | (~test_mode)) & (~kill_clock_en_gated);
   assign slow_clock_en    = (((ShiftReg_SCAN_OUT & (~fast_capture_mode)) | scan_en) & test_mode) | inject_tck | (shift_only_mode & scan_en);
   assign clock_mux_select = ((scan_en | (~fast_capture_mode)) & test_mode) | inject_tck | (shift_only_mode & scan_en);
 

</code>

===== - Parent mode =====
Parent-mode operation is one of the operating modes of the standard OCC.

This operating mode bypasses the OCC clock gating logic and performs clock selection only. \\
It requires a downstream child-mode OCC to perform the clock gating and chopping.

Parent-mode, 父OCC只做时钟function clk 与shift clk之间进行切换，不做OCC的pluse gateing(这部分由child-OCC来实现)

tile parent mode OCC + child OCC, 类似于OCC复制

**非SSN场景**\\
top parent mode OCC + n个tile内部child OCC,无需单独shift clock连线到tile，tile内部也不用单独check shift timing \\

如果多个top parent mode OCC(频率不同) + tile child OCC, function模式下不同频率时钟为异步关系，切换到shift模式下，全为shift时钟，scan register单chain存在skew，需要插入latch


**SSN场景**\\
shfit clock都是走tile内部(由SSH产生)，intest时不考虑tile与tile之间的shift clock skew差异，这时用标准OCC是最好的。

===== - Child OCC =====
SSN好像是不支持child OCC

Child OCC有两种实现：
  * 普通OCC的child mode
  * child-only的OCC

<code>
# 级联OCC会报R27问题， 配置成Parent OCC mode + child OCC mode就不会报这个问题。
add_core_instances -inst [get_inst top_rtl2_tessent_occ_parent_*] \
                         -parameter {parent_mode on fast_capture_mode on}
set_static_dft_signal_values retargeting3_mode 1
//set_drc_handling R27 warning
set_core_instance_parameters -instances \
            coreb_i1/coreb_rtl2_tessent_occ_clka_inst -parameter_values \
            {active_upstream_parent_occ on}
set_core_instance_parameters -instances \
            coreb_i1/coreb_rtl2_tessent_occ_clkb_inst -parameter_values \
            {active_upstream_parent_occ on}
set_core_instance_parameters -instances \
            coreb_i1/coreb_rtl2_tessent_occ_clkc_inst -parameter_values \
            {active_upstream_parent_occ on}
</code>


===== - sync OCC =====

==== - 使用场景 ====
对于分频时钟和不分频时钟之间path当做同步处理的情况，需要使用同步OCC。

在任何场景下，intest/extest, 分频只能发生在第一级sync-occ， 后级的sync occ只能是使用前级sync-occ的时钟输出。
  - intest时，模块sync-occ工作，顶层sync-occ穿通，测试模块内部的path
  - extest时，模块sync-occ穿通，顶层sync-occ工作，测试模块之间的path

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{{:edastudy:tessent:pasted:20250807-123023.png?nolink}}

{{:edastudy:tessent:pasted:20250807-123029.png?nolink}}


==== - 限制 ====
sync occ后面不能接分频时钟。

{{:edastudy:tessent:pasted:20250807-123124.png?nolink}}

原则是任何测试模式的情况下都只能有一级OCC在工作，如果非得用本地的分频，基本上只有在intest情况下才有机会。

extest情况下，只能使用root处的分频，因为同步OCC的限制是pulse是用低频来shift的，必须保证低频shift一致。
==== - 波形 ====
有两种配置， 我理解分别cover 低频到高频，高频到低频。

出capture pulse, 是使用低频时钟来出pulse的，高频在对应的位置点采用gating的方式，保证也只出2个pulse

{{:edastudy:tessent:pasted:20250807-122732.png?nolink}}