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microwatt/sim_uart.vhdl

136 lines
4.1 KiB
VHDL

-- Sim console UART, provides the same interface as potato UART by
-- Kristian Klomsten Skordal.
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
library work;
use work.wishbone_types.all;
use work.sim_console.all;
--! @brief Simple UART module.
--! The following registers are defined:
--! |--------------------|--------------------------------------------|
--! | Address | Description |
--! |--------------------|--------------------------------------------|
--! | 0x00 | Transmit register (write-only) |
--! | 0x08 | Receive register (read-only) |
--! | 0x10 | Status register (read-only) |
--! | 0x18 | Sample clock divisor register (dummy) |
--! | 0x20 | Interrupt enable register (read/write) |
--! |--------------------|--------------------------------------------|
--!
--! The status register contains the following bits:
--! - Bit 0: receive buffer empty
--! - Bit 1: transmit buffer empty
--! - Bit 2: receive buffer full
--! - Bit 3: transmit buffer full
--!
--! Interrupts are enabled by setting the corresponding bit in the interrupt
--! enable register. The following bits are available:
--! - Bit 0: data received (receive buffer not empty)
--! - Bit 1: ready to send data (transmit buffer empty)
entity pp_soc_uart is
generic(
FIFO_DEPTH : natural := 64 --Unused
);
port(
clk : in std_logic;
reset : in std_logic;
-- UART ports:
txd : out std_logic;
rxd : in std_logic;
-- Interrupt signal:
irq : out std_logic;
-- Wishbone ports:
wb_adr_in : in std_logic_vector(11 downto 0);
wb_dat_in : in std_logic_vector( 7 downto 0);
wb_dat_out : out std_logic_vector( 7 downto 0);
wb_we_in : in std_logic;
wb_cyc_in : in std_logic;
wb_stb_in : in std_logic;
wb_ack_out : out std_logic
);
end entity pp_soc_uart;
architecture behaviour of pp_soc_uart is
signal sample_clk_divisor : std_logic_vector(7 downto 0);
-- IRQ enable signals:
signal irq_recv_enable, irq_tx_ready_enable : std_logic := '0';
-- Wishbone signals:
type wb_state_type is (IDLE, WRITE_ACK, READ_ACK);
signal wb_state : wb_state_type;
signal wb_ack : std_logic; --! Wishbone acknowledge signal
begin
wb_ack_out <= wb_ack and wb_cyc_in and wb_stb_in;
-- For the sim console, the transmit buffer is always empty, so always
-- interrupt if enabled. No recieve interrupt.
irq <= irq_tx_ready_enable;
wishbone: process(clk)
variable sim_tmp : std_logic_vector(63 downto 0);
begin
if rising_edge(clk) then
if reset = '1' then
wb_ack <= '0';
wb_state <= IDLE;
sample_clk_divisor <= (others => '0');
irq_recv_enable <= '0';
irq_tx_ready_enable <= '0';
else
case wb_state is
when IDLE =>
if wb_cyc_in = '1' and wb_stb_in = '1' then
if wb_we_in = '1' then -- Write to register
if wb_adr_in(11 downto 0) = x"000" then
sim_console_write(x"00000000000000" & wb_dat_in);
elsif wb_adr_in(11 downto 0) = x"018" then
sample_clk_divisor <= wb_dat_in;
elsif wb_adr_in(11 downto 0) = x"020" then
irq_recv_enable <= wb_dat_in(0);
irq_tx_ready_enable <= wb_dat_in(1);
end if;
wb_ack <= '1';
wb_state <= WRITE_ACK;
else -- Read from register
if wb_adr_in(11 downto 0) = x"008" then
sim_console_read(sim_tmp);
wb_dat_out <= sim_tmp(7 downto 0);
elsif wb_adr_in(11 downto 0) = x"010" then
sim_console_poll(sim_tmp);
wb_dat_out <= "00000" & sim_tmp(0) & '1' & not sim_tmp(0);
elsif wb_adr_in(11 downto 0) = x"018" then
wb_dat_out <= sample_clk_divisor;
elsif wb_adr_in(11 downto 0) = x"020" then
wb_dat_out <= (0 => irq_recv_enable,
1 => irq_tx_ready_enable,
others => '0');
else
wb_dat_out <= (others => '0');
end if;
wb_ack <= '1';
wb_state <= READ_ACK;
end if;
end if;
when WRITE_ACK|READ_ACK =>
if wb_stb_in = '0' then
wb_ack <= '0';
wb_state <= IDLE;
end if;
end case;
end if;
end if;
end process wishbone;
end architecture behaviour;