Source code for hwtLib.peripheral.uart.tx

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

from hwt.code import If, Concat
from hwt.hdl.types.bits import HBits
from hwt.hdl.types.defs import BIT
from hwt.hwIOs.std import HwIODataRdVld, HwIOSignal
from hwt.hwIOs.utils import addClkRstn, propagateClkRstn
from hwt.hwModule import HwModule
from hwt.hwParam import HwParam
from hwt.pyUtils.typingFuture import override
from hwtLib.clocking.clkBuilder import ClkBuilder


# http://ece-research.unm.edu/jimp/vhdl_fpgas/slides/UART.pdf


class UartTx(HwModule):
    """
    UART Tx channel controller

    .. hwt-autodoc::
    """
    @override
    def hwConfig(self):
        self.CLK_FREQ = HwParam(int(100e6))
        # number of bits per second
        self.BAUD = HwParam(115200)
        # self.PARITY = HwParam(None)

    @override
    def hwDeclr(self):
        addClkRstn(self)
        self.dataIn = HwIODataRdVld()
        self.dataIn.DATA_WIDTH = 8
        self.txd = HwIOSignal()._m()

    @override
    def hwImpl(self):
        propagateClkRstn(self)
        r = self._reg

        START_BIT = BIT.from_py(0)
        STOP_BIT = BIT.from_py(1)
        BITS_TO_SEND = 1 + 8 + 1
        BIT_RATE = self.CLK_FREQ // self.BAUD

        assert BIT_RATE >= 1

        din = self.dataIn

        data = r("data", HBits(BITS_TO_SEND))  # data + start bit + stop bit
        en = r("en", def_val=False)
        tick, last = ClkBuilder(self, self.clk).timers(
                                                       [BIT_RATE, BIT_RATE * BITS_TO_SEND],
                                                       en)

        If(~en & din.vld,
           data(Concat(STOP_BIT, din.data, START_BIT)),
           en(1)
        ).Elif(tick & en,
            # srl where 1 is shifted from left
            data(BIT.from_py(1)._concat(data[:1])),
            If(last,
               en(0),
            )
        )
        din.rd(~en)

        txd = r("reg_txd", def_val=1)
        If(tick & en,
           txd(data[0])
        )
        self.txd(txd)



if __name__ == "__main__":
    from hwt.synth import to_rtl_str
    
    m = UartTx()
    print(to_rtl_str(m))