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defmodule Circuits.UART.Framing.FourByte do
@behaviour Circuits.UART.Framing
@moduledoc """
Each message is 4 bytes. This framer doesn't do anything for the transmit
direction, but for receives, it will collect bytes in batches of 4 before
sending them up. The user can set up a framer timeout if they don't mind
partial frames. This can be useful to resyncronize when bytes are dropped.
"""
def init(_args) do
{:ok, <<>>}
end
def add_framing(data, rx_buffer) when is_binary(data) do
# No processing - assume the app knows to send the right number of bytes
{:ok, data, rx_buffer}
end
def frame_timeout(rx_buffer) do
# On a timeout, just return whatever was in the buffer
{:ok, [rx_buffer], <<>>}
end
def flush(:transmit, rx_buffer), do: rx_buffer
def flush(:receive, _rx_buffer), do: <<>>
def flush(:both, _rx_buffer), do: <<>>
def remove_framing(data, rx_buffer) do
process_data(rx_buffer <> data, [])
end
defp process_data(<<message::binary-size(4), rest::binary>>, messages) do
process_data(rest, messages ++ [message])
end
defp process_data(<<>>, messages) do
{:ok, messages, <<>>}
end
defp process_data(partial, messages) do
{:in_frame, messages, partial}
end
end