tx_encoder.vhd

为提高8051系列单片机I2C总线的工作效率

         else
            if spdif_clk_en = '1' then  -- SPDIF clock is twice the bit rate
               case framest is
                  when IDLE =>
                     bit_cnt      <= 0;
                     frame_cnt    <= 0;
                     inv_preamble <= '0';
                     toggle       <= '0';
                     framest      <= BLOCK_START;
                  when BLOCK_START =>   -- Start of channels status block/Ch. A
                     evt_lcsbf    <= '0';
                     evt_hcsbf    <= '0';
                     chb_samp_ack <= '0';
                     toggle       <= not toggle;  -- Each bit uses two clock enables,
                     if toggle = '1' then         -- counted by the toggle bit.
                        if bit_cnt < 31 then
                           bit_cnt <= bit_cnt + 1;
                        else
                           bit_cnt <= 0;
                           if send_audio = '1' then
                              cha_samp_ack <= '1';
                           end if;
                           framest <= CHANNEL_B;
                        end if;
                     end if;
                     -- Block start uses preamble Z.
                     if bit_cnt < 4 then
                        if toggle = '0' then
                           spdif_out <= Z_PREAMBLE(2 * bit_cnt) xor inv_preamble;
                        else
                           spdif_out <= Z_PREAMBLE(2 * bit_cnt + 1) xor inv_preamble;
                        end if;
                        par_cnt <= 0;
                     elsif bit_cnt > 3 and bit_cnt <= 31 then
                        spdif_out <= encode_bit(bit_cnt, valid, frame_cnt,
                                                par_cnt, active_user_data,
                                                active_ch_status,
                                                audio, toggle, spdif_out);
                        if bit_cnt = 31 then
                           inv_preamble <= encode_bit(bit_cnt, valid, frame_cnt,
                                                      par_cnt, active_user_data,
                                                      active_ch_status,
                                                      audio, toggle, spdif_out);
                        end if;
                        if toggle = '0' then
                           if bit_cnt > 3 and bit_cnt < 31 and
                              par_vector(bit_cnt - 4) = '1' then
                              par_cnt <= par_cnt + 1;
                           end if;
                        end if;
                     end if;
                  when CHANNEL_A =>     -- Sub-frame: channel A.
                     evt_lcsbf    <= '0';
                     evt_hcsbf    <= '0';
                     chb_samp_ack <= '0';
                     toggle       <= not toggle;
                     if toggle = '1' then
                        if bit_cnt < 31 then
                           bit_cnt <= bit_cnt + 1;
                        else
                           bit_cnt <= 0;
                           if spdif_out = '1' then
                              inv_preamble <= '1';
                           else
                              inv_preamble <= '0';
                           end if;
                           if send_audio = '1' then
                              cha_samp_ack <= '1';
                           end if;
                           framest <= CHANNEL_B;
                        end if;
                     end if;
                     -- Channel A uses preable X.
                     if bit_cnt < 4 then
                        if toggle = '0' then
                           spdif_out <= X_PREAMBLE(2 * bit_cnt) xor inv_preamble;
                        else
                           spdif_out <= X_PREAMBLE(2 * bit_cnt + 1) xor inv_preamble;
                        end if;
                        par_cnt <= 0;
                     elsif bit_cnt > 3 and bit_cnt <= 31 then
                        spdif_out <= encode_bit(bit_cnt, valid, frame_cnt,
                                                par_cnt, active_user_data,
                                                active_ch_status,
                                                audio, toggle, spdif_out);
                        if bit_cnt = 31 then
                           inv_preamble <= encode_bit(bit_cnt, valid, frame_cnt,
                                                      par_cnt, active_user_data,
                                                      active_ch_status,
                                                      audio, toggle, spdif_out);
                        end if;
                        if toggle = '0' then
                           if bit_cnt > 3 and bit_cnt < 31 and
                              par_vector(bit_cnt - 4) = '1' then
                              par_cnt <= par_cnt + 1;
                           end if;
                        end if;
                     end if;
                  when CHANNEL_B =>     -- Sub-frame: channel B.
                     cha_samp_ack <= '0';
                     toggle       <= not toggle;
                     if toggle = '1' then
                        if bit_cnt < 31 then
                           bit_cnt <= bit_cnt + 1;
                        else
                           bit_cnt <= 0;
                           valid   <= not conf_txdata;
                           if spdif_out = '1' then
                              inv_preamble <= '1';
                           else
                              inv_preamble <= '0';
                           end if;
                           send_audio <= conf_txdata;  -- 1 if audio samples sohuld be sent
                           if send_audio = '1' then
                              chb_samp_ack <= '1';
                           end if;
                           if frame_cnt < 191 then  -- One block is 192 frames
                              frame_cnt <= frame_cnt + 1;
                              if frame_cnt = 96 then
                                 evt_lcsbf <= '1';
                              end if;
                              framest <= CHANNEL_A;
                           else
                              frame_cnt <= 0;
                              evt_hcsbf <= '1';
                              framest   <= BLOCK_START;
                           end if;
                        end if;
                     end if;
                     -- Channel B uses preable Y.
                     if bit_cnt < 4 then
                        if toggle = '0' then
                           spdif_out <= Y_PREAMBLE(2 * bit_cnt) xor inv_preamble;
                        else
                           spdif_out <= Y_PREAMBLE(2 * bit_cnt + 1) xor inv_preamble;
                        end if;
                        par_cnt <= 0;
                     elsif bit_cnt > 3 and bit_cnt <= 31 then
                        spdif_out <= encode_bit(bit_cnt, valid, frame_cnt,
                                                par_cnt, active_user_data,
                                                active_ch_status,
                                                audio, toggle, spdif_out);
                        if bit_cnt = 31 then
                           inv_preamble <= encode_bit(bit_cnt, valid, frame_cnt,
                                                      par_cnt, active_user_data,
                                                      active_ch_status,
                                                      audio, toggle, spdif_out);
                        end if;
                        if toggle = '0' then
                           if bit_cnt > 3 and bit_cnt < 31 and
                              par_vector(bit_cnt - 4) = '1' then
                              par_cnt <= par_cnt + 1;
                           end if;
                        end if;
                     end if;
                  when others =>
                     framest <= IDLE;
               end case;
            end if;
         end if;
      end if;
   end process FRST;

-- Audio data latching
   DA32 : if DATA_WIDTH = 32 generate
      ALAT : process (wb_clk_i)
      begin
         if rising_edge(wb_clk_i) then
            if send_audio = '0' then
               audio(23 downto 0) <= (others => '0');
            else
               case to_integer(unsigned(conf_mode)) is
                  when 0 =>             -- 16 bit audio
                     audio(23 downto 8) <= sample_data(15 downto 0);
                     audio(7 downto 0)  <= (others => '0');
                  when 1 =>             -- 17 bit audio
                     audio(23 downto 7) <= sample_data(16 downto 0);
                     audio(6 downto 0)  <= (others => '0');
                  when 2 =>             -- 18 bit audio
                     audio(23 downto 6) <= sample_data(17 downto 0);
                     audio(5 downto 0)  <= (others => '0');
                  when 3 =>             -- 19 bit audio
                     audio(23 downto 5) <= sample_data(18 downto 0);
                     audio(4 downto 0)  <= (others => '0');
                  when 4 =>             -- 20 bit audio
                     audio(23 downto 4) <= sample_data(19 downto 0);
                     audio(3 downto 0)  <= (others => '0');
                  when 5 =>             -- 21 bit audio
                     audio(23 downto 3) <= sample_data(20 downto 0);
                     audio(2 downto 0)  <= (others => '0');
                  when 6 =>             -- 22 bit audio
                     audio(23 downto 2) <= sample_data(21 downto 0);
                     audio(1 downto 0)  <= (others => '0');
                  when 7 =>             -- 23 bit audio
                     audio(23 downto 1) <= sample_data(22 downto 0);
                     audio(0)           <= '0';
                  when 8 =>             -- 24 bit audio
                     audio(23 downto 0) <= sample_data(23 downto 0);
                  when others =>        -- unsupported modes
                     audio(23 downto 0) <= (others => '0');
               end case;
            end if;
         end if;
      end process ALAT;
   end generate DA32;

   DA16 : if DATA_WIDTH = 16 generate
      ALAT : process (wb_clk_i)
      begin
         if rising_edge(wb_clk_i) then
            if send_audio = '0' then
               audio(23 downto 0) <= (others => '0');
            else
               audio(23 downto 8) <= sample_data(15 downto 0);
               audio(7 downto 0)  <= (others => '0');
            end if;
         end if;
      end process ALAT;
   end generate DA16;

-- Parity vector. These bits are counted to generate even parity
   par_vector(23 downto 0) <= audio(23 downto 0);
   par_vector(24)          <= valid;
   par_vector(25)          <= active_user_data(frame_cnt);
   par_vector(26)          <= active_ch_status(frame_cnt);

-- Channel status and user datat to be used if buffers are disabled.
-- User data is then all zero, while channel status bits are taken from
-- register TxChStat.
   def_user_data(191 downto 0) <= (others => '0');
   def_ch_status(0)            <= '0';           -- consumer mode
   def_ch_status(1)            <= chstat_audio;  -- audio bit
   def_ch_status(2)            <= chstat_copy;   -- copy right
   def_ch_status(5 downto 3)   <= "000" when chstat_preem = '0'
                                else "001";      -- pre-emphasis
   def_ch_status(7 downto 6)   <= "00";
   def_ch_status(14 downto 8)  <= (others => '0');
   def_ch_status(15)           <= chstat_gstat;  -- generation status
   def_ch_status(23 downto 16) <= (others => '0');
   def_ch_status(27 downto 24) <= "0000" when chstat_freq = "00" else
                                  "0010" when chstat_freq = "01" else
                                  "0011" when chstat_freq = "10" else
                                  "0001";
   def_ch_status(191 downto 28) <= (others => '0');

-- Generate channel status vector based on configuration register setting.
   active_ch_status <= ch_stat_a when conf_chsten = "01" else
                       ch_stat_a when conf_chsten = "10" and framest = CHANNEL_A else
                       ch_stat_b when conf_chsten = "10" and framest = CHANNEL_B else
                       def_ch_status;

-- Generate user data vector based on configuration register setting.
   active_user_data <= user_data_a when conf_udaten = "01" else
                       user_data_a when conf_udaten = "10" and framest = CHANNEL_A else
                       user_data_b when conf_udaten = "10" and framest = CHANNEL_B else
                       def_user_data;
   
end rtl;