bl0x / learn-fpga-amaranth Goto Github PK

In part 05, with m.FSM is used, and fsm.state is used within the with block. However, this causes an error which states that FSM doesn't have a property state. If you try to access fsm.state after exiting the with block, it works.

Also, 05, but not 06 and later, lacks domain="slow" in the FSM constructor, which I think is incorrect.

I noticed that the LOAD state wasn't being reached even though isLoad was active. Looking at Bruno's code it is using ternary operator to select state which, for Amaranth, I believe you can either use Mux or m.Elif. So, I changed the Execute state from:

                with m.If(~isSystem):
                    m.d.sync += pc.eq(nextPc)
                with m.If(isLoad):
                    m.next = "LOAD"
                with m.If(isStore):
                    m.next = "STORE"
                with m.Else():                      <-- this overrides because isStore isn't active
                    m.next = "FETCH_INSTR"

to:

                with m.If(~isSystem):
                    m.d.sync += pc.eq(nextPc)
                with m.If(isLoad):
                    m.next = "LOAD"
                with m.Elif(isStore):                   <---- change is here
                    m.next = "STORE"
                with m.Else():
                    m.next = "FETCH_INSTR"

which makes it work correctly. However, my mind says that m.If should also work. However, the problem is with the m.Else part. This is being triggered because isStore isn't active which overrides the LOAD state!

The simulations use .add_sync_process(), which emits a deprecation warning.

I am very new to Amaranth, so I may be missing something, but .add_process() appears to work just fine.