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pipelining of reading from rom

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This commit is contained in:
Raphael Jacquot 2019-03-14 14:33:28 +01:00
parent c30b96d1af
commit e97ec2243f
2 changed files with 36 additions and 8 deletions
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4
saturn_bus.v
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@ -67,8 +67,12 @@ saturn_hp48gx_rom hp48gx_rom (
.i_clk (i_clk),
.i_clk_en (i_clk_en),
.i_reset (i_reset),
`ifdef SIM
.i_phase (phase),
.i_cycle_ctr (cycle_ctr),
`endif
.i_phase_0 (phases[0]),
.i_debug_cycle (dbg_debug_cycle),
.i_bus_clk_en (bus_clk_en),
.i_bus_is_data (ctrl_bus_is_data),

38
saturn_hp48gx_rom.v
View file

@ -32,9 +32,12 @@ module saturn_hp48gx_rom (
i_clk,
i_clk_en,
i_reset,
`ifdef SIM
i_phase,
i_cycle_ctr,
`endif
i_phase_0,
i_debug_cycle,
i_bus_clk_en,
i_bus_is_data,
o_bus_nibble_out,
@ -44,13 +47,17 @@ module saturn_hp48gx_rom (
input wire [0:0] i_clk;
input wire [0:0] i_clk_en;
input wire [0:0] i_reset;
`ifdef SIM
input wire [1:0] i_phase;
input wire [31:0] i_cycle_ctr;
`endif
input wire [0:0] i_phase_0;
input wire [0:0] i_debug_cycle;
input wire [0:0] i_bus_clk_en;
input wire [0:0] i_bus_is_data;
output reg [3:0] o_bus_nibble_out;
input wire [3:0] i_bus_nibble_in;
input wire [0:0] i_bus_clk_en;
input wire [0:0] i_bus_is_data;
output reg [3:0] o_bus_nibble_out;
input wire [3:0] i_bus_nibble_in;
reg [3:0] rom_data[0:(2**`ROMBITS)-1];
initial $readmemh("rom-gx-r.hex", rom_data, 0, (2**`ROMBITS)-1);
@ -59,6 +66,7 @@ reg [3:0] last_cmd;
reg [2:0] addr_pos_ctr;
reg [19:0] local_pc;
reg [19:0] local_dp;
reg [3:0] read_nibble;
initial begin
last_cmd = 4'b0;
@ -74,6 +82,9 @@ end
wire [0:0] do_pc_read = (last_cmd == `BUSCMD_PC_READ);
wire [0:0] do_dp_read = (last_cmd == `BUSCMD_DP_READ);
wire [0:0] do_read = do_pc_read || do_dp_read;
/* pre-read happens on phase 0 */
wire [0:0] pre_read = i_clk_en && i_phase_0 && !i_debug_cycle && do_read;
/* this happes on phase 1 */
wire [0:0] can_read = i_bus_clk_en && i_bus_is_data && do_read;
wire [19:0] access_pointer = do_pc_read?local_pc:local_dp;
@ -86,8 +97,21 @@ wire [19:`ROMBITS-1] access_pointer_unused = access_pointer[19:`ROMBITS-1];
wire [`ROMBITS-1:0] address = access_pointer[`ROMBITS-1:0];
always @(posedge i_clk) begin
if (can_read)
o_bus_nibble_out <= rom_data[address];
if (pre_read) begin
`ifdef SIM
$display("ROM-GX-R %0d: [%d] pre_read %h <= rom[%5h]", i_phase, i_cycle_ctr, rom_data[address], address);
`endif
read_nibble <= rom_data[address];
end
end
always @(posedge i_clk) begin
if (can_read) begin
`ifdef SIM
$display("ROM-GX-R %0d: [%d] can_read %h <= rom[%5h]", i_phase, i_cycle_ctr, read_nibble, address);
`endif
o_bus_nibble_out <= read_nibble;
end
end
`ifdef SIM