rgb2ycbcr.py

def rgb2ycbcr(rgb, ycbcr, clock, reset):
    """ A RGB to YCbCr converter with reset.

    Arguments:
        rgb: red, green, blue interface
               r: input 8-bit unsigned value in range of 0-255
               g: input 8-bit unsigned value in range of 0-255
               b: input 8-bit unsigned value in range of 0-255

        ycbcr: the luma-chroma interace
            y: output 8-bit unsigned value in range of 0-127
            cb: output 8-bit unsigned value in range of 0-128
            cr:  output 8-bit unsigned value in range of 0-128

        clock: system clock
        reset: system reset

    """

    temp_nbits = PRECISION_FACTOR + ycbcr.bitlength()
    ytemp, cbtemp, crtemp = [intbv(0)[temp_nbits:] for _ in range(3)]

    @always_seq(clk.posedge, reset=reset)
    def logic():
        ycbcr.valid.next = False

        if rgb.valid:
            yscale = Y_OFFSET + ((Y1 * rgb.red) + (Y2 * rgb.green) + 
                                 (Y3 * rgb.blue))
            ytemp[:] = yscale # intbv(Y_OFFSET + Y1 * rgb.red +
                              # Y2 * rgb.green + Y3 * rgb.blue)[temp_nbits-1:]

            cbscale = CB_OFFSET + ((CB1 * rgb.red) + (CB2 * rgb.green) + 
                                    (CB3 * rgb.blue))

            cbtemp[:] = cbscale # intbv(CB_OFFSET + CB1 * rgb.red +
                                # CB2 * rgb.green + CB3 * rgb.blue)[temp_nbits-1:]

            crscale = CR_OFFSET + ((CR1 * rgb.red) + (CR2 * rgb.green) + 
                                  (CR3 * rgb.blue))
            crtemp[:] = crscale # intbv(CR_OFFSET + CR1 * rgb.red +
                                # CR2 * rgb.green + CR3 * rgb.blue)[temp_nbits-1:]

            ycbcr.y.next = round_unsigned(
                ytemp, temp_nbits, PRECISION_FACTOR)

            ycbcr.cb.next = round_unsigned(
                cbtemp, temp_nbits, PRECISION_FACTOR)

            ycbcr.cr.next = round_unsigned(
                crtemp, temp_nbits, PRECISION_FACTOR)

            ycbcr.valid.next = True
    return logic

round_unsigned.py

def round_unsigned(val, msb, lsb):
    rval = int(val[msb:lsb])
    if val[lsb - 1]:
        rval = int(val[msb:lsb]) + 1

    return rval