1, WARNING: Xst: 737 - Found 8-bit latch for signal .
WARNING: Xst: 1895 - Due to other FF/Latch trimming, FF/Latch (without init value) has a constant value of 0 in block .
Cause: All conditions are not flushed in the state machine, or the output in the state machine is not initialized.
Solution: Add the default statement at the end of the case condition, and assign an initial value to the output signal before the case statement.
2, WARNING: Xst: 2170 - Unit TXMGR: the following signal (s) form a combinatorial loop:
Explain that the output of the combinatorial logic is connected back to the input of the combinatorial logic, forming a loop. The combinatorial logic cannot be like this.
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