litex/examples/wb_initiator.py

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# Copyright (C) 2012 Vermeer Manufacturing Co.
# License: GPLv3 with additional permissions (see README).
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from random import Random
from migen.fhdl.structure import *
from migen.fhdl import autofragment
from migen.bus.transactions import *
from migen.bus import wishbone
from migen.sim.generic import Simulator
from migen.sim.icarus import Runner
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# Our bus master.
# Python generators let us program bus transactions in an elegant sequential style.
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def my_generator():
prng = Random(92837)
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# Write to the first addresses.
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for x in range(10):
t = TWrite(x, 2*x)
yield t
print("Wrote in " + str(t.latency) + " cycle(s)")
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# Insert some dead cycles to simulate bus inactivity.
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for delay in range(prng.randrange(0, 3)):
yield None
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# Read from the first addresses.
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for x in range(10):
t = TRead(x)
yield t
print("Read " + str(t.data) + " in " + str(t.latency) + " cycle(s)")
for delay in range(prng.randrange(0, 3)):
yield None
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# Our bus slave.
# All transactions complete with a random delay.
# Reads return address + 4. Writes are simply acknowledged.
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class MyPeripheral:
def __init__(self):
self.bus = wishbone.Interface()
self.ack_en = Signal()
self.prng = Random(763627)
def do_simulation(self, s):
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# Only authorize acks on certain cycles to simulate variable latency.
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s.wr(self.ack_en, self.prng.randrange(0, 2))
def get_fragment(self):
comb = [
self.bus.ack.eq(self.bus.cyc & self.bus.stb & self.ack_en),
self.bus.dat_r.eq(self.bus.adr + 4)
]
return Fragment(comb, sim=[self.do_simulation])
def main():
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# The "wishbone.Initiator" library component runs our generator
# and manipulates the bus signals accordingly.
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master = wishbone.Initiator(my_generator())
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# Our slave.
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slave = MyPeripheral()
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# The "wishbone.Tap" library component examines the bus at the slave port
# and displays the transactions on the console (<TRead...>/<TWrite...>).
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tap = wishbone.Tap(slave.bus)
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# Connect the master to the slave.
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intercon = wishbone.InterconnectPointToPoint(master.bus, slave.bus)
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# A small extra simulation function to terminate the process when
# the initiator is done (i.e. our generator is exhausted).
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def end_simulation(s):
s.interrupt = master.done
fragment = autofragment.from_local() + Fragment(sim=[end_simulation])
sim = Simulator(fragment, Runner())
sim.run()
main()
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# Output:
# <TWrite adr:0x0 dat:0x0>
# Wrote in 0 cycle(s)
# <TWrite adr:0x1 dat:0x2>
# Wrote in 0 cycle(s)
# <TWrite adr:0x2 dat:0x4>
# Wrote in 0 cycle(s)
# <TWrite adr:0x3 dat:0x6>
# Wrote in 1 cycle(s)
# <TWrite adr:0x4 dat:0x8>
# Wrote in 1 cycle(s)
# <TWrite adr:0x5 dat:0xa>
# Wrote in 2 cycle(s)
# ...
# <TRead adr:0x0 dat:0x4>
# Read 4 in 2 cycle(s)
# <TRead adr:0x1 dat:0x5>
# Read 5 in 2 cycle(s)
# <TRead adr:0x2 dat:0x6>
# Read 6 in 1 cycle(s)
# <TRead adr:0x3 dat:0x7>
# Read 7 in 1 cycle(s)
# ...