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frontend/wishbone: simplify/review and get FSM back (ease comprehension).

This commit is contained in:
Florent Kermarrec 2020-08-05 11:05:00 +02:00
parent 47a0d5fb9e
commit 4970c8aa8c
1 changed files with 37 additions and 30 deletions
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67
litedram/frontend/wishbone.py
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@ -36,37 +36,44 @@ class LiteDRAMWishbone2Native(Module):
adr_offset = base_address >> log2_int(port.data_width//8) adr_offset = base_address >> log2_int(port.data_width//8)
# latch ready signals of cmd/wdata and then wait until all are ready # Write Datapath ---------------------------------------------------------------------------
cmd_consumed = Signal()
wdata_consumed = Signal()
self.sync += [
If(wishbone.ack,
cmd_consumed.eq(0),
wdata_consumed.eq(0),
).Else(
If(port.cmd.valid & port.cmd.ready, cmd_consumed.eq(1)),
If(port.wdata.valid & port.wdata.ready, wdata_consumed.eq(1)),
),
]
ack_cmd = Signal()
ack_wdata = Signal()
ack_rdata = Signal()
self.comb += [ self.comb += [
port.cmd.addr.eq(wishbone.adr - adr_offset),
port.cmd.we.eq(wishbone.we),
port.wdata.data.eq(wishbone.dat_w), port.wdata.data.eq(wishbone.dat_w),
port.wdata.we.eq(wishbone.sel), port.wdata.we.eq(wishbone.sel),
wishbone.dat_r.eq(port.rdata.data),
# always wait for reads, flush write when transaction ends
port.flush.eq(~wishbone.cyc),
port.cmd.last.eq(~wishbone.we),
# make sure cmd/wdata won't stay valid after it is consumed
port.cmd.valid.eq(wishbone.cyc & wishbone.stb & ~cmd_consumed),
port.wdata.valid.eq((port.cmd.valid | cmd_consumed) & port.cmd.we & ~wdata_consumed),
port.rdata.ready.eq((port.cmd.valid | cmd_consumed) & ~port.cmd.we),
wishbone.ack.eq(ack_cmd & ((wishbone.we & ack_wdata) | (~wishbone.we & ack_rdata))),
ack_cmd.eq((port.cmd.valid & port.cmd.ready) | cmd_consumed),
ack_wdata.eq((port.wdata.valid & port.wdata.ready) | wdata_consumed),
ack_rdata.eq(port.rdata.valid & port.rdata.ready),
] ]
# Read Datapath ----------------------------------------------------------------------------
self.comb += [
wishbone.dat_r.eq(port.rdata.data),
]
# Control ----------------------------------------------------------------------------------
self.submodules.fsm = fsm = FSM(reset_state="CMD")
fsm.act("CMD",
port.flush.eq(~wishbone.cyc), # Flush write when transaction ends.
port.cmd.last.eq(~wishbone.we), # Always wait for reads.
port.cmd.valid.eq(wishbone.cyc & wishbone.stb),
port.cmd.we.eq(wishbone.we),
port.cmd.addr.eq(wishbone.adr - adr_offset),
If(port.cmd.valid & port.cmd.ready,
If(wishbone.we,
NextState("WAIT-WRITE")
).Else(
NextState("WAIT-READ")
)
)
)
fsm.act("WAIT-WRITE",
port.wdata.valid.eq(1),
If(port.wdata.ready,
wishbone.ack.eq(1),
NextState("CMD")
)
)
fsm.act("WAIT-READ",
port.rdata.ready.eq(1),
If(port.rdata.valid,
wishbone.ack.eq(1),
NextState("CMD")
)
)