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AppleIISd
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AppleIISd/VHDL/AppleIISd.vhd

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----------------------------------------------------------------------------------
-- Company: n/a
-- Engineer: A. Fachat
--
-- Create Date: 12:37:11 05/07/2011
-- Design Name: SPI65B
-- Module Name: SPI6502B - Behavioral
-- Project Name: CS/A NETUSB 2.0
-- Target Devices: CS/A NETUSB 2.0
-- Tool versions:
-- Description: An SPI interface for 6502-based computers (or compatible).
-- modelled after the SPI65 interface by Daryl Rictor
-- (see http://sbc.rictor.org/io/65spi.html )
-- This implementation here, however, is a complete reimplementation
-- as the ABEL language of the original implementation is not supported
-- by ISE anymore.
-- Also I added the interrupt input handling, replacing four of the
-- original SPI select outputs with four interrupt inputs
-- Also folded out the single MISO input into one input for each of the
-- four supported devices, reducing external parts count again by one.
--
-- Dependencies:
--
-- Revision:
-- Revision 0.01 - File Created
-- Revision 0.02 - removed spiclk and replaced with clksrc and clkcnt_is_zero combination,
-- to drive up SPI clock to half of input clock (and not one fourth only as before)
-- unfortunately that costed one divisor bit to fit into the CPLD
-- Additional Comments:
--
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity AppleIISd is
Port (
data : inout STD_LOGIC_VECTOR (7 downto 0);
nrw : in STD_LOGIC;
nreset : in STD_LOGIC;
addr : in STD_LOGIC_VECTOR (1 downto 0);
clk_phi0 : in STD_LOGIC;
ndev_sel : in STD_LOGIC;
clk_7m : in STD_LOGIC;
spi_miso: in std_logic;
spi_mosi : out STD_LOGIC;
spi_sclk : out STD_LOGIC;
spi_Nsel : out STD_LOGIC;
wp : in STD_LOGIC;
card : in STD_LOGIC;
led : out STD_LOGIC;
a8 : in std_logic;
a9 : in std_logic;
a10 : in std_logic;
nio_sel : in std_logic;
nio_stb : in std_logic;
b8 : out std_logic;
b9 : out std_logic;
b10 : out std_logic;
noe : out std_logic;
ng : out std_logic
);
constant DIV_WIDTH : integer := 3;
end AppleIISd;
architecture Behavioral of AppleIISd is
-- interface signals
signal selected: std_logic;
signal reset: std_logic;
signal is_read: std_logic;
signal int_din: std_logic_vector (7 downto 0);
signal int_dout: std_logic_vector (7 downto 0);
signal int_mosi: std_logic;
signal int_miso: std_logic;
signal int_sclk: std_logic;
--------------------------
-- internal state
signal spidatain: std_logic_vector (7 downto 0);
signal spidataout: std_logic_vector (7 downto 0);
signal inited: std_logic; -- card initialized
signal inited_set: std_logic;
-- spi register flags
signal tc: std_logic; -- transmission complete; cleared on spi data read
signal bsy: std_logic; -- SPI busy
signal frx: std_logic; -- fast receive mode
signal tmo: std_logic; -- tri-state mosi
signal ece: std_logic; -- external clock enable; 0=phi2, 1=external clock
signal cpol: std_logic; -- shift clock polarity; 0=rising edge, 1=falling edge
signal cpha: std_logic; -- shift clock phase; 0=leading edge, 1=rising edge
signal divisor: std_logic_vector(DIV_WIDTH-1 downto 0);
signal slavesel: std_logic; -- slave select output (0=selected)
--------------------------
-- helper signals
-- shift engine
signal start_shifting: std_logic; -- shifting data
signal shifting2: std_logic; -- shifting data
signal shiftdone: std_logic; -- shifting data done
signal shiftcnt: std_logic_vector(3 downto 0); -- shift counter (5 bit)
-- spi clock
signal clksrc: std_logic; -- clock source (phi2 or clk_7m)
-- TODO divcnt is not used at all??
signal divcnt: std_logic_vector(DIV_WIDTH-1 downto 0); -- divisor counter
signal shiftclk : std_logic;
component AddressDecoder
port (
A8 : in std_logic;
A9 : in std_logic;
A10 : in std_logic;
CLK : in std_logic;
NDEV_SEL : in std_logic;
NIO_SEL : in std_logic;
NIO_STB : in std_logic;
RNW : in std_logic;
B8 : out std_logic;
B9 : out std_logic;
B10 : out std_logic;
NOE : out std_logic
);
end component;
begin
add_dec : AddressDecoder
port map (
A8 => a8,
A9 => a9,
A10 => a10,
CLK => clk_7m,
NDEV_SEL => ndev_sel,
NIO_SEL => nio_sel,
NIO_STB => nio_stb,
RNW => nrw,
B8 => b8,
B9 => b9,
B10 => b10,
NOE => noe);
led <= not (inited_set);
--led <= not (bsy or not slavesel);
ng <= ndev_sel and nio_sel and nio_stb;
bsy <= start_shifting or shifting2;
process(clk_7m, reset, card, inited_set)
begin
if(reset = '1' or card = '1') then
inited <= '0';
elsif rising_edge(inited_set) then
inited <= '1';
end if;
end process;
process(start_shifting, shiftdone, shiftclk)
begin
if (rising_edge(shiftclk)) then
if (shiftdone = '1') then
shifting2 <= '0';
else
shifting2 <= start_shifting;
end if;
end if;
end process;
process(shiftcnt, reset, shiftclk)
begin
if (reset = '1') then
shiftdone <= '0';
elsif (rising_edge(shiftclk)) then
if (shiftcnt = "1111") then
shiftdone <= '1';
else
shiftdone <= '0';
end if;
end if;
end process;
process(reset, shifting2, shiftcnt, shiftclk)
begin
if (reset='1') then
shiftcnt <= (others => '0');
elsif (rising_edge(shiftclk)) then
if (shifting2 = '1') then
-- count phase
shiftcnt <= shiftcnt + 1;
else
shiftcnt <= (others => '0');
end if;
end if;
end process;
inproc: process(reset, shifting2, shiftcnt, shiftclk, spidatain, int_miso)
begin
if (reset='1') then
spidatain <= (others => '0');
elsif (rising_edge(shiftclk)) then
if (shifting2 = '1' and shiftcnt(0) = '1') then
-- shift in to input register
spidatain (7 downto 1) <= spidatain (6 downto 0);
spidatain (0) <= int_miso;
end if;
end if;
end process;
outproc: process(reset, shifting2, spidataout, cpol, cpha, shiftcnt, shiftclk)
begin
if (reset='1') then
int_mosi <= '1';
int_sclk <= cpol;
else
-- clock is sync'd
if (rising_edge(shiftclk)) then
if (shifting2='0' or shiftdone = '1') then
int_mosi <= '1';
int_sclk <= cpol;
else
-- output data directly from output register
case shiftcnt(3 downto 1) is
when "000" => int_mosi <= spidataout(7);
when "001" => int_mosi <= spidataout(6);
when "010" => int_mosi <= spidataout(5);
when "011" => int_mosi <= spidataout(4);
when "100" => int_mosi <= spidataout(3);
when "101" => int_mosi <= spidataout(2);
when "110" => int_mosi <= spidataout(1);
when "111" => int_mosi <= spidataout(0);
when others => int_mosi <= '1';
end case;
int_sclk <= cpol xor cpha xor shiftcnt(0);
end if;
end if;
end if;
end process;
-- shift operation enable
shiften: process(reset, selected, nrw, addr, frx, shiftdone)
begin
-- start shifting
if (reset='1' or shiftdone='1') then
start_shifting <= '0';
elsif (falling_edge(selected) and addr="00" and (frx='1' or nrw='0')) then
-- access to register 00, either write (nrw=0) or fast receive bit set (frx)
-- then both types of access (write but also read)
start_shifting <= '1';
end if;
end process;
--------------------------
-- spiclk - spi clock generation
-- spiclk is still 2 times the freq. than sclk
clksrc <= clk_phi0 when (ece = '0') else clk_7m;
-- is a pulse signal to allow for divisor==0
--shiftclk <= clksrc when divcnt = "000000" else '0';
shiftclk <= clksrc when bsy = '1' else '0';
clkgen: process(reset, divisor, clksrc)
begin
if (reset='1') then
divcnt <= divisor;
elsif (falling_edge(clksrc)) then
if (shiftclk = '1') then
divcnt <= divisor;
else
divcnt <= divcnt - 1;
end if;
end if;
end process;
--------------------------
-- interface section
-- inputs
reset <= not (nreset);
selected <= not(ndev_sel);
int_din <= data;
int_miso <= (spi_miso and not slavesel);
process(selected, clk_7m)
begin
if(selected = '0') then
is_read <= '0';
elsif(rising_edge(clk_7m) and selected = '1' and clk_phi0 = '1' and nrw = '1') then
is_read <= '1';
end if;
end process;
-- outputs
data <= int_dout when (is_read='1') else (others => 'Z'); -- data bus tristate
spi_sclk <= int_sclk;
spi_mosi <= int_mosi when tmo='0' else 'Z'; -- mosi tri-state
spi_Nsel <= slavesel;
tc_proc: process (selected, shiftdone)
begin
if (shiftdone = '1') then
tc <= '1';
elsif (falling_edge(selected) and addr="00") then
tc <= '0';
end if;
end process;
--------------------------
-- cpu register section
-- cpu read
cpu_read: process (is_read, addr,
spidatain, tc, bsy, frx, tmo, ece, cpol, cpha, divisor,
slavesel, wp, card, inited)
begin
if (is_read = '1') then
case addr is
when "00" => -- read SPI data in
int_dout <= spidatain;
when "01" => -- read status register
int_dout(0) <= cpha;
int_dout(1) <= cpol;
int_dout(2) <= ece;
int_dout(3) <= tmo;
int_dout(4) <= frx;
int_dout(5) <= bsy;
int_dout(6) <= '0';
int_dout(7) <= tc;
when "10" => -- read sclk divisor
int_dout(DIV_WIDTH-1 downto 0) <= divisor;
int_dout(7 downto 3) <= (others => '0');
when "11" => -- read slave select / slave interrupt state
int_dout(0) <= slavesel;
int_dout(4 downto 1) <= (others => '0');
int_dout(5) <= wp;
int_dout(6) <= card;
int_dout(7) <= inited;
when others =>
int_dout <= (others => '0');
end case;
else
int_dout <= (others => '0');
end if;
end process;
-- cpu write
cpu_write: process(reset, selected, nrw, addr, int_din, card, inited)
begin
if (reset = '1') then
cpha <= '0';
cpol <= '0';
ece <= '0';
tmo <= '0';
frx <= '0';
slavesel <= '1';
divisor <= (others => '0');
spidataout <= (others => '1');
inited_set <= '0';
elsif (card = '1') then
inited_set <= '0';
elsif (falling_edge(selected) and nrw = '0') then
case addr is
when "00" => -- write SPI data out (see other process above)
spidataout <= int_din;
when "01" => -- write status register
cpha <= int_din(0);
cpol <= int_din(1);
ece <= int_din(2);
tmo <= int_din(3);
frx <= int_din(4);
-- no bit 5 - 7
when "10" => -- write divisor
divisor <= int_din(DIV_WIDTH-1 downto 0);
when "11" => -- write slave select / slave interrupt enable
slavesel <= int_din(0);
-- no bit 1 - 6
inited_set <= int_din(7);
when others =>
end case;
end if;
end process;
end Behavioral;
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