litex/miscope/bridges/uart2csr/uart.py

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from migen.fhdl.structure import *
from migen.fhdl.module import Module
from migen.genlib.cdc import MultiReg
from migen.bank.description import *
from migen.bank.eventmanager import *
class UART(Module):
def __init__(self, clk_freq, baud=115200):
self.rx_ev = Signal()
self.rx_dat = Signal(8)
self.tx_we = Signal()
self.tx_ev = Signal()
self.tx_dat = Signal(8)
self.divisor = Signal(16, reset=int(clk_freq/baud/16))
self.tx = Signal(reset=1)
self.rx = Signal()
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###
enable16 = Signal()
enable16_counter = Signal(16)
self.comb += enable16.eq(enable16_counter == 0)
self.sync += [
enable16_counter.eq(enable16_counter - 1),
If(enable16,
enable16_counter.eq(self.divisor - 1))
]
# TX
tx_reg = Signal(8)
tx_bitcount = Signal(4)
tx_count16 = Signal(4)
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tx_done = self.tx_ev
tx_busy = Signal()
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self.sync += [
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tx_done.eq(0),
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If(self.tx_we,
tx_reg.eq(self.tx_dat),
tx_bitcount.eq(0),
tx_count16.eq(1),
tx_busy.eq(1),
self.tx.eq(0)
).Elif(enable16 & tx_busy,
tx_count16.eq(tx_count16 + 1),
If(tx_count16 == 0,
tx_bitcount.eq(tx_bitcount + 1),
If(tx_bitcount == 8,
self.tx.eq(1)
).Elif(tx_bitcount == 9,
self.tx.eq(1),
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tx_busy.eq(0),
tx_done.eq(1)
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).Else(
self.tx.eq(tx_reg[0]),
tx_reg.eq(Cat(tx_reg[1:], 0))
)
)
)
]
# RX
rx = Signal()
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self.specials += MultiReg(self.rx, rx, "sys")
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rx_r = Signal()
rx_reg = Signal(8)
rx_bitcount = Signal(4)
rx_count16 = Signal(4)
rx_busy = Signal()
rx_done = self.rx_ev
rx_data = self.rx_dat
self.sync += [
rx_done.eq(0),
If(enable16,
rx_r.eq(rx),
If(~rx_busy,
If(~rx & rx_r, # look for start bit
rx_busy.eq(1),
rx_count16.eq(7),
rx_bitcount.eq(0)
)
).Else(
rx_count16.eq(rx_count16 + 1),
If(rx_count16 == 0,
rx_bitcount.eq(rx_bitcount + 1),
If(rx_bitcount == 0,
If(rx, # verify start bit
rx_busy.eq(0)
)
).Elif(rx_bitcount == 9,
rx_busy.eq(0),
If(rx, # verify stop bit
rx_data.eq(rx_reg),
rx_done.eq(1)
)
).Else(
rx_reg.eq(Cat(rx_reg[1:], rx))
)
)
)
)
]