| commit | 474d74afd1bad8b3edec2bf7ee9635bdbddc92be | [log] [tgz] |
|---|---|---|
| author | Martin Lueker-Boden <martin.lueker-boden@wdc.com> | Mon Aug 29 19:11:05 2022 -0700 |
| committer | Martin Lueker-Boden <47870387+martin-lueker@users.noreply.github.com> | Wed Sep 07 15:19:56 2022 -0700 |
| tree | 8b7ac215e0cb7ed052254e95075cc6e238158c04 | |
| parent | 779e8f1b895f14f2f12d2a2bdcb5fef39a418472 [diff] |
[entropy_src/rtl] Provide backpressure on core FIFOs The DV changes added in PR #14643 immediately revealed that there are some gaps in the backpressure pipeline in the entropy_src core, and that stalls from the cs_aes_halt_ack can cause entropy to be dropped before it gets SHA conditioner, which could lead to poor entropy outputs if enough entropy is dropped. This PR corrects the problem by applying consistent backpressure throughout the entropy_src data processing chain. With a long enough delay entropy can be stalled all the way back at the RNG input. Even if the external RNG source does not support backpressure, this is fine because entropy dropped at the is not counted when calculating the number of inputs gathered to create the output seeds. Applying backpressure all the way back to the RNG input also helps for verification, as the test environement does support backpressure at this interface. ----- This commit also manipulates the timing of the internal enable signals, as the new backpressure changes introduce one timing wrinkle. Since RNG bit-select mode introduces an additional packer fifo stage this creates a one cycle delay that comes and goes whether the RNG bit select fifo is enabled, which can cause dropped samples at disable time, and these particular samples are difficult to handle in verification. Therefore the enable/disable signal for most of the core is delayed by one additional clock cycle. This delayed enable signal is only used by processing stages after the RNG bit select FIFO (which is most of the core). Inputs to the bit-select and RNG input FIFOs use separate enable signals. Signed-off-by: Martin Lueker-Boden <martin.lueker-boden@wdc.com> Co-authored-by: Mark Branstad <mark.branstad@wdc.com>
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