+ comment about buffer channels

        @param histogram_height_m1 - one less than window height. If 0 - use frame bottom margin (end of VACT)

        @param reset_afi            Reset AFI multiplexer when initializing

        2018/01/02: the buffer sizes and addresses can be read from sysfs.

                    /sys/devices/soc0/elphel393-mem@0/buffer_address_circbuf_chn0..3, buffer_address_raw_chn0..3

                    buffer_pages_circbuf_chn0..3,   buffer_pages_raw_chn0..3, page size is 4096

        @param circbuf_chn_size - circular buffer size for each channel, in bytes

        @param verbose - verbose level

        @return True if all done, False if exited prematurely by  exit_step

        """