PLL integration example + FlatChipTop/TestHarness

[jerryz123]

• Provides a new WithPLLSelectorDividerClockGenerator to replace the default WithDividerOnlyClockGenerator. WithPLLSelectorDividerClockGenerator adds regmapped clock-mux, clock-divider, and a fake PLL with regmapped control. The intention is for future chips to create custom clock binders following this pattern
• Adds a ChipConfigs file with ChipLikeRocketConfig, that sets up crossings, clock gen, I/O more realistically.
• Adds FlatChipTop and FlatTestHarness, to demonstrate how to use a custom TestHarness+ChipTop with Chipyard, bypassing the IOBinders/HarnessBinders if necessary (this should only be done as a last resort).

make CONFIG=ChipLikeRocketConfig run-binary BINARY=../../tests/hello.riscv

For custom ChipTop/TestHarness... do

make CONFIG=ChipLikeRocketConfig MODEL_PACKAGE=chipyard.example MODEL=FlatTestHarness run-binary BINARY=../../tests/hello.riscv

Related PRs / Issues:

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

Contributor Checklist:

• Did you set main as the base branch?
• Is this PR's title suitable for inclusion in the changelog and have you added a changelog:<topic> label?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• Did you mark the PR with a changelog: label?
• (If applicable) Did you update the conda .conda-lock.yml file if you updated the conda requirements file?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you add a test demonstrating the PR?

• (If applicable) Did you mark the PR as Please Backport?

[harrisonliew]

Looks good for the most part without testing.

[noahgaertner]

Does this require/assume the PLL is actually a PLL (because internal clock/external clock edges need to be synchronous or something), or could some other clock multiplier be inserted instead?

[jerryz123]

The FakePLL in WithPLLSelectorDividerClockGenerator can be replaced with any block that emits clocks.