// ZX-Evo Base Configuration (c) NedoPC 2008,2009,2010,2011,2012,2013,2014
//
// Z80 memory manager: routes ROM/RAM accesses, makes wait-states for 14MHz or stall condition, etc.
/*
This file is part of ZX-Evo Base Configuration firmware.
ZX-Evo Base Configuration firmware is free software:
you can redistribute it and/or modify it under the terms of
the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
ZX-Evo Base Configuration firmware is distributed in the hope that
it will be useful, but WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with ZX-Evo Base Configuration firmware.
If not, see <http://www.gnu.org/licenses/>.
*/
//
// fclk _/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\_/`\
// | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
// zclk /```\___/```\___/```\___/```````\_______/```````\_______/```````````````\_______________/```````````````\_______________/`
// | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
// zpos `\___/```\___/```\___/```\___________/```\___________/```\___________________________/```\___________________________/```\
// | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
// zneg _/```\___/```\___/```\_______/```\___________/```\___________________/```\___________________________/```\________________
`include "../include/tune.v"
module zmem(
input wire fclk,
input wire rst_n,
input wire zpos, //
input wire zneg, // strobes which show positive and negative edges of zclk
input wire cbeg, // DRAM synchronization
input wire post_cbeg, //
input wire pre_cend, //
input wire cend, //
input wire [15:0] za,
input wire [ 7:0] zd_in, // won't emit anything to Z80 bus, data bus mux is another module
output wire [ 7:0] zd_out, // output to Z80 bus
output wire zd_ena, // out bus to the Z80
input wire m1_n,
input wire rfsh_n,
input wire mreq_n,
input wire iorq_n,
input wire rd_n,
input wire wr_n,
input wire [ 1:0] int_turbo, // 2'b00 - 3.5,
// 2'b01 - 7.0,
// 2'b1x - 14.0
input wire win0_romnram, // four windows, each 16k,
input wire win1_romnram, // ==1 - there is rom,
input wire win2_romnram, // ==0 - there is ram
input wire win3_romnram, //
input wire [ 7:0] win0_page, // which 16k page is in given window
input wire [ 7:0] win1_page, //
input wire [ 7:0] win2_page, //
input wire [ 7:0] win3_page, //
input wire win0_wrdisable, // ==1 - no write is possible to window
input wire win1_wrdisable,
input wire win2_wrdisable,
input wire win3_wrdisable,
input wire romrw_en,
output reg [ 4:0] rompg, // output for ROM paging
output wire romoe_n,
output wire romwe_n,
output wire csrom,
output wire cpu_req,
output wire cpu_rnw,
output wire [20:0] cpu_addr,
output wire [ 7:0] cpu_wrdata,
output wire cpu_wrbsel,
input wire [15:0] cpu_rddata,
input wire cpu_next,
input wire cpu_strobe,
output wire cpu_stall // for zclock
);
wire [1:0] win;
reg [7:0] page;
reg romnram;
reg wrdisable;
reg [15:0] rd_buf;
reg [15:1] cached_addr;
reg cached_addr_valid;
wire cache_hit;
wire dram_beg;
wire opfetch, memrd, memwr;
wire stall14, stall7_35;
wire stall14_ini;
wire stall14_cyc;
reg stall14_cycrd;
reg stall14_fin;
reg r_mreq_n;
reg pending_cpu_req;
reg cpu_rnw_r;
// this is for 7/3.5mhz
wire ramreq;
wire ramwr,ramrd;
wire cpureq_357;
reg ramrd_reg,ramwr_reg;
// make paging
assign win[1:0] = za[15:14];
always @*
case( win )
2'b00: begin
page = win0_page;
romnram = win0_romnram;
wrdisable = win0_wrdisable;
end
2'b01: begin
page = win1_page;
romnram = win1_romnram;
wrdisable = win1_wrdisable;
end
2'b10: begin
page = win2_page;
romnram = win2_romnram;
wrdisable = win2_wrdisable;
end
2'b11: begin
page = win3_page;
romnram = win3_romnram;
wrdisable = win3_wrdisable;
end
endcase
// rom paging - only half a megabyte addressing.
always @*
begin
rompg[4:0] = page[4:0];
end
assign romwe_n = wr_n | mreq_n | (~romrw_en) | wrdisable;
assign romoe_n = rd_n | mreq_n;
assign csrom = romnram; // positive polarity!
// 7/3.5mhz support
assign ramreq = (~mreq_n) && (~romnram) && rfsh_n;
assign ramrd = ramreq & (~rd_n);
assign ramwr = (ramreq & (~wr_n)) & (~wrdisable);
always @(posedge fclk)
if( cend && (!cpu_stall) )
begin
ramrd_reg <= ramrd;
ramwr_reg <= ramwr;
end
assign cpureq_357 = ( ramrd & (~ramrd_reg) ) | ( ramwr & (~ramwr_reg) );
assign zd_ena = (~mreq_n) & (~rd_n) & (~romnram);
assign cache_hit = ( (za[15:1] == cached_addr[15:1]) && cached_addr_valid );
// strobe the beginnings of DRAM cycles
always @(posedge fclk)
if( zneg )
r_mreq_n <= mreq_n | (~rfsh_n);
//
assign dram_beg = ( (!cache_hit) || memwr ) && zneg && r_mreq_n && (!romnram) && (!mreq_n) && rfsh_n;
// access type
assign opfetch = (~mreq_n) && (~m1_n);
assign memrd = (~mreq_n) && (~rd_n);
assign memwr = (~mreq_n) && rd_n && rfsh_n && (!wrdisable);
// wait tables:
//
// M1 opcode fetch, dram_beg coincides with:
// cend: +3
// pre_cend: +4
// post_cbeg: +5
// cbeg: +6
//
// memory read, dram_beg coincides with:
// cend: +2
// pre_cend: +3
// post_cbeg: +4
// cbeg: +5
//
// memory write: no wait
//
// special case: if dram_beg pulses 1 when cpu_next is 0,
// unconditional wait has to be performed until cpu_next is 1, and
// then wait as if dram_beg would coincide with cbeg
assign stall14_ini = dram_beg && ( (!cpu_next) || opfetch || memrd ); // no wait at all in write cycles, if next dram cycle is available
// memrd, opfetch - wait till cend & cpu_next,
// memwr - wait till cpu_next
assign stall14_cyc = memwr ? (!cpu_next) : stall14_cycrd;
//
always @(posedge fclk, negedge rst_n)
if( !rst_n )
stall14_cycrd <= 1'b0;
else // posedge fclk
begin
if( cpu_next && cend )
stall14_cycrd <= 1'b0;
else if( dram_beg && ( (!cend) || (!cpu_next) ) && (opfetch || memrd) )
stall14_cycrd <= 1'b1;
end
//
always @(posedge fclk, negedge rst_n)
if( !rst_n )
stall14_fin <= 1'b0;
else // posedge fclk
begin
if( stall14_fin && ( (opfetch&pre_cend) || (memrd&post_cbeg) ) )
stall14_fin <= 1'b0;
else if( cpu_next && cend && cpu_req && (opfetch || memrd) )
stall14_fin <= 1'b1;
end
//
assign cpu_stall = int_turbo[1] ? (stall14_ini | stall14_cyc | stall14_fin) : (cpureq_357 && (!cpu_next));
// cpu request
assign cpu_req = int_turbo[1] ? (pending_cpu_req | dram_beg) : cpureq_357;
//
assign cpu_rnw = int_turbo[1] ? (dram_beg ? (!memwr) : cpu_rnw_r) : ramrd;
//
//
always @(posedge fclk, negedge rst_n)
if( !rst_n )
pending_cpu_req <= 1'b0;
else if( cpu_next && cend )
pending_cpu_req <= 1'b0;
else if( dram_beg )
pending_cpu_req <= 1'b1;
//
always @(posedge fclk)
if( dram_beg )
cpu_rnw_r <= !memwr;
// address, data in and data out
//
assign cpu_wrbsel = za[0];
assign cpu_addr[20:0] = { page[7:0], za[13:1] };
assign cpu_wrdata = zd_in;
//
always @* if( cpu_strobe ) // WARNING! ACHTUNG! LATCH!!!
rd_buf <= cpu_rddata;
//
assign zd_out = cpu_wrbsel ? rd_buf[7:0] : rd_buf[15:8];
wire io;
reg io_r;
//
assign io = (~iorq_n);
//
always @(posedge fclk)
if( zpos )
io_r <= io;
//
always @(posedge fclk, negedge rst_n)
if( !rst_n )
begin
cached_addr_valid <= 1'b0;
end
else
begin
if( (zneg && r_mreq_n && (!mreq_n) && rfsh_n && romnram) ||
(zneg && r_mreq_n && memwr ) ||
(io && (!io_r) && zpos ) )
cached_addr_valid <= 1'b0;
else if( cpu_strobe )
cached_addr_valid <= 1'b1;
end
//
always @(posedge fclk)
if( !rst_n )
begin
cached_addr <= 15'd0;
end
else if( cpu_strobe )
begin
cached_addr[15:1] <= za[15:1];
end
endmodule