F2 Clock Recipes User Guide

Table of Content

• F2 Clock Recipes User Guide

  • Table of Content

  • Introduction

  • F2 Clock Recipe Tables

  • How to Specify Clock Recipe During Build Time

  • How to Dynamically Configure Clocks during Runtime

  • Clock Consideration When Porting CL Designs from F1 into F2

  • References

Introduction

F2 Shell offers two clocks - clk_main_a0 and clk_hbm_ref to the CL. This is different from F1 Shell, which offers total of 8 clocks from Shell to the CL as described in F1 Shell Interface Spec. Offering fewer clocks from the Shell to CL is beneficial because it does not lock up the routing resources for customers who do not require all the clocks from the Shell.

The clk_main_a0 defaults to 250MHz. Dynamic reconfiguration of the frequency for clk_main_a0 is currently NOT supported. However, this will be supported in future.

The clk_hbm_ref is a fixed frequency 100MHz clock required for the HBM IP to clock the APB interface.

F2 Developer Kit provides a clocking IP AWS_CLK_GEN for customers who desire to have same clocks and clock recipe support as F1. Tables below shows the clock recipes supported in F2.

F2 Clock Recipe Tables

Clock Group A
Recipe Number	clk_main_a0	clk_extra_a1	clk_extra_a2	clk_extra_a3	Notes
A0	250	62.5	187.5	250	AWS_CLK_GEN is not required in the CL design for clk_main_a0 recipes. clk_extra_a0/a1/a2 clocks require AWS_CLK_GEN block instantiated in CL design.
A1	250	125	375	500
A2	250	15.625	125	62.5

Clock Group B
Recipe Number	clk_extra_b0	clk_extra_b1			Notes
B0	250	125			clk_extra_b0/b1 require AWS _CLK_GEN block instantiated in the CL design.
B1	125	62.5
B2	450	225
B3	250	62.5
B4	300	75
B5	400	100

Clock Group C
Recipe Number	clk_extra_c0	clk_extra_c1			Notes
C0	300	400
C1	150	200
C2	75	100
C3	200	266.667

Clock Group HBM
Recipe Number	clk_hbm_axi				Notes
H0	300	400			clk _hbm_axi requires AWS_CLK_GEN IP instantiated in the CL design. The clk _hbm_axi is used to clock the AXI interfaces of HBM IP. This clock is not available in F1.
H1	125
H2	450
H3	300
H4	400

Reference Clock Group
Recipe Number	clk_hbm_ref				Notes
	100				Fixed frequency 100MHz reference clock from the Shell for HBM IP.

NOTE: clk_main_a0 supports A0, A1 and A2 clock recipes without requiring AWS_CLK_GEN IP instantiated in the CL design. All other clocks and their respective clock recipes require AWS_CLK_GEN IP instantiated in the CL design and interfaced to the SDA interface from the Shell. CL_MEM_PERF demonstrates how AWS_CLK_GEN is integrated into CL design.

How to Specify Clock Recipe During Build Time

Developers who wish to build CL design for a specific clock frequency defined in the F2 Clock Recipe Tables can do so by passing the following arguments at the time of CL builds. Specifying clock recipe at the time of build, automatically adjusts the design clock constraints enabling the Vivado tool to close timing of CL based on chosen clock frequency.

For example, command below shows CL_MEM_PERF built using user specified clock recipes:

cd $CL_DIR/build/scripts/
./aws_build_dcp_from_cl.py --cl=cl_mem_perf --clock_recipe_a=A0 --clock_recipe_b=B3 --clock_recipe_c=C3 --clock_recipe_hbm=H4

When the clock recipe options are not explicitly specified, aws_build_dcp_from_cl.py defaults to --clock_recipe_a=A1 --clock_recipe_b=B2 --clock_recipe_c=C0 --clock_recipe_hbm=H2

NOTE: If AWS_CLK_GEN IP is not instantiated in the CL design, the recipes for AWS_CLK_GEN clocks will be ignored. Users may see CRITICAL WARNING related to missing AWS_CLK_GEN instantiation during builds.

How to Dynamically Configure Clocks during Runtime

Support for SW API to do clock frequency dynamic configuration is available using the fpga-load-clkgen-dynamic and fpga-load-clkgen-recipe command line interfaces detailed in Amazon FPGA Image (AFI) Management Tools.

Clock Consideration When Porting CL Designs from F1 into F2

1. The clk_main_a0 is now fixed at 250MHz. It does not support clock recipes or dynamic frequency reconfiguration. However, they will be supported in future.

2. F1 designs that relied on additional clocks such as clk_extra_* will now have two options in F2:

   a. Customers can instantiate required number of MMCMs in their CL design to meet the clocking requirement.

   b. Alternately, customers can instantiate AWS_CLK_GEN IP in their CL which offers same set of clocks from F1, in addition to clk_hbm_axi for HBM clocking. AWS provides SW APIs to simplify clock configuration for the user application.

3. F2 supports same clock recipe build switches as F1 to simplify porting of F1 designs into F2.

References

F1 Dynamic Clock Configuration

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