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// Part of NeoGS project
//
// FPGA early and on-the-fly configuration, Z80 clock switch,
// 3.3v RAM buffer
//
// (c) 2008-2010 NedoPC
module GS_cpld(
output reg config_n, // ACEX1K config pins
input wire status_n, //
input wire conf_done, //
output wire cs, //
input wire init_done, //
input wire clk24in, // 24mhz in
input wire clk20in, // 20mhz in
input wire clksel0, // clock select 0 (1=divide by 2, 0=no divide)
input wire clksel1, // clock select 1 (1=clk20in, 0=clk24in)
output wire clkout, // clock out
input wire clkin, // input of clkout signal, buffered, same as for Z80
input wire coldres_n, // resets
output reg warmres_n,
input wire iorq_n, // Z80 control signals
input wire mreq_n,
input wire rd_n,
input wire wr_n,
inout wire [ 7:0] d, // Z80 data bus
input wire a6, // some Z80 addresses
input wire a7,
input wire a10,
input wire a11,
input wire a12,
input wire a13,
input wire a14,
input wire a15,
output wire mema14,
output wire mema15,
output wire mema19,
inout wire romcs_n,
inout wire memoe_n,
inout wire memwe_n,
input wire in_ramcs0_n,
input wire in_ramcs1_n,
input wire in_ramcs2_n,
input wire in_ramcs3_n,
output wire out_ramcs0_n,
output wire out_ramcs1_n,
output wire ra6, // some buffered memory addresses
output wire ra7,
output wire ra10,
output wire ra11,
output wire ra12,
output wire ra13,
inout wire [ 7:0] rd // memory data bus
);
reg int_mema14,int_mema15;
reg int_romcs_n,int_ramcs_n;
wire int_memoe_n,int_memwe_n;
wire int_cs;
wire ext_romcs_n,
ext_memoe_n,
ext_memwe_n;
reg [1:0] memcfg; // memcfg[1]: 1 ram, 0 roms
// memcfg[0]: 0 page0, 1 page1 -> in 8000-ffff region
reg disbl; // =1 - cpld disabled, =0 - enabled
reg was_cold_reset_n; // 1 - no cold reset, 0 - was cold reset
reg [1:0] dbout;
wire [1:0] dbin;
wire memcfg_write_n;
wire rescfg_write_n;
wire coldrstf_read_n;
wire fpgastat_read_n;
assign dbin[1] = d[7];
assign dbin[0] = d[0];
reg [3:0] rstcount; // counter for warm reset period
reg [2:0] disbl_sync;
// PORTS:
// {a7,a6}
// 00 - fpga ports
// 01,WR - write memcfg: d7=RAM(1)/ROM(0), d0=32k page(0/1)
// 01,RD - read cold_reset_n flag: d7=(0:was cold reset,1:no cold reset)
// 10,WR - set cold_reset_n flag & write FPGA nCONFIG: d7=1: set cold_reset_n flag, d0: nCONFIG
// 10,RD - read FPGA status: d7=nSTATUS, d0=CONF_DONE
// 11,WR - write to FPGA
// 11,RD - read from FPGA
// clock selector
clocker clk( .clk1(clk24in),
.clk2(clk20in),
.clksel(clksel1),
.divsel(clksel0),
.clkout(clkout)
);
// disable control
always @(negedge config_n,posedge init_done)
begin
if( !config_n ) // asynchronous reset
disbl <= 0;
else // posedge of init_done, synchronous set
disbl <= 1;
end
// memory control pins when running without configured FPGA
assign mema14 = disbl ? 1'bZ : int_mema14;
assign mema15 = disbl ? 1'bZ : int_mema15;
assign romcs_n = disbl ? 1'bZ : int_romcs_n;
assign memoe_n = disbl ? 1'bZ : int_memoe_n;
assign memwe_n = disbl ? 1'bZ : int_memwe_n;
assign cs = disbl ? 1'bZ : int_cs;
assign ext_romcs_n = romcs_n;
assign ext_memoe_n = memoe_n;
assign ext_memwe_n = memwe_n;
// controlling memory paging
always @*
begin
casex( {a15,a14,memcfg[1]} )
3'b00x:
{int_mema15,int_mema14,int_romcs_n,int_ramcs_n} <= 4'b0001;
3'b01x:
{int_mema15,int_mema14,int_romcs_n,int_ramcs_n} <= 4'b0010;
3'b1x0:
{int_mema15,int_mema14,int_romcs_n,int_ramcs_n} <= {memcfg[0],a14,2'b01};
3'b1x1:
{int_mema15,int_mema14,int_romcs_n,int_ramcs_n} <= {memcfg[0],a14,2'b10};
endcase
end
// controlling memory /OE, /WE
assign int_memoe_n = mreq_n | rd_n;
assign int_memwe_n = mreq_n | wr_n;
// writing paging register [1:0] memcfg
assign memcfg_write_n = iorq_n | wr_n | a7 | ~a6; // {a7,a6}==01
always @(negedge coldres_n, posedge memcfg_write_n)
begin
if( !coldres_n ) // reset on coldres_n
memcfg <= 2'b00;
else // write on memcfg_write_n
memcfg <= dbin;
end
// writing nCONFIG and cold reset "register"
assign rescfg_write_n = iorq_n | wr_n | ~a7 | a6; // {a7,a6}==10
always @(posedge rescfg_write_n, negedge coldres_n)
begin
if( !coldres_n ) // async reset
begin
was_cold_reset_n <= 0; // there was!
config_n <= 0; // start FPGA config
end
else // sync set/load
begin
config_n <= dbin[0];
was_cold_reset_n <= dbin[1] | was_cold_reset_n;
end
end
// controlling positive CS pin to FPGA
assign int_cs = a7 & a6; // {a7,a6}==11
// reading control
assign coldrstf_read_n = iorq_n | rd_n | a7 | ~a6; // {a7,a6}=01
assign fpgastat_read_n = iorq_n | rd_n | ~a7 | a6; // {a7,a6}=10
always @*
begin
case( {coldrstf_read_n,fpgastat_read_n} )
2'b01:
dbout = { was_cold_reset_n, 1'bX };
2'b10:
dbout = { status_n, conf_done };
default:
dbout = 2'bXX;
endcase
end
// warm resetter control
always @(posedge clkin)
begin
disbl_sync[2:0]={disbl_sync[1:0],disbl};
end
always @(negedge coldres_n,posedge clkin)
begin
if( coldres_n==0 ) // async reset
begin
rstcount <= (-1);
warmres_n <= 0;
end
else // posedge clkin
begin
if( disbl_sync[2]==0 && disbl_sync[1]==1 ) // positive pulse
begin
warmres_n <= 0;
rstcount <= (-1);
end
else // no disbl_sync positive pulse
begin
rstcount <= rstcount - 1;
if( |rstcount == 0 )
warmres_n <= 1'bZ;
end
end
end
// Z80 data bus control
assign d = ( (!coldrstf_read_n)||(!fpgastat_read_n) ) ?
{ dbout[1], 6'bXXXXXX, dbout[0] } :
( (ext_romcs_n&&(!ext_memoe_n)) ? rd : 8'bZZZZZZZZ ) ;
// memory data bus control
assign rd = (ext_romcs_n&&(!ext_memwe_n)) ? d : 8'bZZZZZZZZ;
// memory addresses buffering
assign ra6 = a6;
assign ra7 = a7;
assign ra10 = a10;
assign ra11 = a11;
assign ra12 = a12;
assign ra13 = a13;
// memory CS'ing
assign out_ramcs0_n = disbl ? ( in_ramcs0_n & in_ramcs1_n ) : int_ramcs_n;
assign out_ramcs1_n = disbl ? ( in_ramcs2_n & in_ramcs3_n ) : 1'b1;
assign mema19 = disbl ? ( in_ramcs0_n & in_ramcs2_n ) : 1'b0;
endmodule