Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 4/01/2024
Public

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A.4.3.1. FPGA User Mode Entry

During an FPGA Boot First Mode, the h2f_gp_out[1] remains low until the HPS software drives it high. The following diagram shows the FPGA user mode entry.

Figure 329. FPGA User Mode - FPGA Boot First

In the following diagram, during an HPS Boot First mode or HPS does an FPGA reconfiguration, the “CPU is operational” line is high throughout.

Figure 330. FPGA User Mode - HPS Boot First
Note: The h2f_gp_out[1] is gated low until some arbitrary delay after nINIT_DONE is asserted low, then the h2f_gp_out[1] is driven with the value of the h2f_gp_out[31:0] register. Software must not set h2f_gp_out[1] = 1 before the FPGA is in User Mode and the specific FPGA logic is ready to be released from reset. This allows the specific FPGA logic to remain inactive even after the SDM gate is released.
Note: If software does set h2f_gp_out[1] = 1 before the FPGA is in user mode, then the SDM gate release event is likely to expose the FPGA logic to an asynchronous race condition between the h2f_user0_clock and the h2f_gp_out[1] signal which may cause logic implementing synchronous resets to miss the reset event altogether.