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6502/65C02: Add power up reset generation (AlanD 65C02 core needs this)

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Change-Id: I8e24d0f724dc353be296546815462feba8dffc4b
This commit is contained in:
David Banks 2019-10-17 11:25:32 +01:00
parent 12338bffc9
commit 9d0e74b94e
2 changed files with 25 additions and 6 deletions
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2
firmware/AtomBusMon.c
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@ -10,7 +10,7 @@
* VERSION and NAME are used in the start-up message * VERSION and NAME are used in the start-up message
********************************************************/ ********************************************************/
#define VERSION "0.80" #define VERSION "0.81"
#if defined(CPU_Z80) #if defined(CPU_Z80)
#define NAME "ICE-Z80" #define NAME "ICE-Z80"

29
src/MOS6502CpuMonCore.vhd
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@ -84,8 +84,10 @@ architecture behavioral of MOS6502CpuMonCore is
signal hold : std_logic; signal hold : std_logic;
signal Addr_int : std_logic_vector(23 downto 0); signal Addr_int : std_logic_vector(23 downto 0);
signal cpu_addr_us: unsigned (15 downto 0); signal cpu_addr_us : unsigned (15 downto 0);
signal cpu_dout_us: unsigned (7 downto 0); signal cpu_dout_us : unsigned (7 downto 0);
signal cpu_reset_n : std_logic;
signal reset_counter : std_logic_vector(9 downto 0);
signal Regs : std_logic_vector(63 downto 0); signal Regs : std_logic_vector(63 downto 0);
signal Regs1 : std_logic_vector(255 downto 0); signal Regs1 : std_logic_vector(255 downto 0);
@ -195,12 +197,30 @@ begin
cpu_clken_ss <= (not hold) and cpu_clken; cpu_clken_ss <= (not hold) and cpu_clken;
-- Generate a short (~1ms @ 1MHz) power up reset pulse
--
-- This is in case FPGA configuration takes longer than
-- the length of the host system reset pulse.
--
-- Some 6502 cores (particularly the AlanD core) needs
-- reset to be asserted to start.
process(cpu_clk)
begin
if rising_edge(cpu_clk) then
if (reset_counter(reset_counter'high) = '0') then
reset_counter <= reset_counter + 1;
end if;
cpu_reset_n <= Res_n_in and reset_counter(reset_counter'high);
end if;
end process;
GenT65Core: if UseT65Core generate GenT65Core: if UseT65Core generate
inst_t65: entity work.T65 port map ( inst_t65: entity work.T65 port map (
mode => "00", mode => "00",
Abort_n => '1', Abort_n => '1',
SO_n => SO_n, SO_n => SO_n,
Res_n => Res_n_in, Res_n => cpu_reset_n,
Enable => cpu_clken_ss, Enable => cpu_clken_ss,
Clk => cpu_clk, Clk => cpu_clk,
Rdy => '1', Rdy => '1',
@ -217,7 +237,7 @@ begin
GenAlanDCore: if UseAlanDCore generate GenAlanDCore: if UseAlanDCore generate
inst_r65c02: entity work.r65c02 port map ( inst_r65c02: entity work.r65c02 port map (
reset => Res_n_in, reset => cpu_reset_n,
clk => cpu_clk, clk => cpu_clk,
enable => cpu_clken_ss, enable => cpu_clken_ss,
nmi_n => NMI_n_masked, nmi_n => NMI_n_masked,
@ -234,7 +254,6 @@ begin
Addr_int(15 downto 0) <= std_logic_vector(cpu_addr_us); Addr_int(15 downto 0) <= std_logic_vector(cpu_addr_us);
end generate; end generate;
-- This block generates a hold signal that acts as the inverse of a clock enable -- This block generates a hold signal that acts as the inverse of a clock enable
-- for the CPU. See comments above for why this is a cycle delayed a cycle. -- for the CPU. See comments above for why this is a cycle delayed a cycle.
hold_gen : process(cpu_clk) hold_gen : process(cpu_clk)