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AIbra11's avatar
AIbra11
Icon for New Contributor rankNew Contributor
4 years ago

Reading inputs in a state-machine

Hello,
I've spent a lot of time trying to get this state machine working with no hope.

Requirement: In this FSM, we want to set:

- opcode_reg and offset_reg to USB3_DATA(3 downto 0) and USB_DATA(15 downto 4) respectively in GET_OPCODE_OFFSET state (and keep its value after that)

- RegLengthCounter to unsigned(USB3_DATA(11 downto 0)), and RegPointer to unsigned(OffsetReg) in GET_LENGTH state. (and keep its value after that)

Here is the code I've written so far (attached), specifically processes:

USB_CLK_PROC and RegProxy_FSM_Proc

Problem:

- The data is registered correctly, but changes at the next clock edge, how can I keep it fixed?

2 Replies

  • sstrell's avatar
    sstrell
    Icon for Super Contributor rankSuper Contributor
    4 years ago

    Follow the LHS (left hand side)!

    Are you sure USB3_DATA isn't changing at all? You have it in a separate assignment (non-clocked logic), so it will update immediately if there is a change:

    USB3_DATA <= USBSendDataOut when USBWrOeRSig = '1' else (others => 'Z');

  • AIbra11's avatar
    AIbra11
    Icon for New Contributor rankNew Contributor
    4 years ago

    Thank you, it was a timing issue, I was wrongly sampling the data at the same edge when it changes.

    Changed sampling moment to be on the opposite clock edge.