// ZX-Evo Base Configuration (c) NedoPC 2008,2009,2010,2011,2012,2013,2014
//
// ATM-like memory pager (it pages specific 16kb region)
// with additions to support 4m addressable memory
// and pent1m mode.
//
// contain ports xFF7, x7F7, xBF7
/*
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/>.
*/
`include "../include/tune.v"
module atm_pager(
input wire rst_n,
input wire fclk,
input wire zpos,
input wire zneg,
input wire [15:0] za, // Z80 address bus
input wire [ 7:0] zd, // Z80 data bus - for latching port data
input wire mreq_n,rd_n,m1_n, // to track DOS turn on/turn off
input wire pager_off, // PEN as in ATM2: turns off memory paging, service ROM is everywhere
input wire pent1m_ROM, // for memory maps switching: d4 of 7ffd
input wire [ 5:0] pent1m_page, // 1 megabyte from pentagon1024 addressing, from 7FFD port
input wire pent1m_ram0_0, // RAM0 to the window 0 from pentagon1024 mode
input wire pent1m_1m_on, // 1 meg addressing of pent1m mode on
input wire in_nmi, // when we are in nmi, in 0000-3FFF must be last (FFth)
// RAM page. analoguous to pent1m_ram0_0
// but has higher priority
input wire in_trdemu, // like 'in_nmi', page 0xFE
input wire atmF7_wr, // write strobe for the xxF7 ATM port
input wire dos, // indicates state of computer: also determines ROM mapping
output wire dos_turn_on, // turns on or off DOS signal
output wire dos_turn_off, //
output wire zclk_stall, // stall Z80 clock during DOS turning on
output reg [ 7:0] page,
output reg romnram,
output reg wrdisable,
// output for xxBE port read
output wire [ 7:0] rd_page0,
output wire [ 7:0] rd_page1,
output wire [ 1:0] rd_dos7ffd,
output wire [ 1:0] rd_ramnrom,
output wire [ 1:0] rd_wrdisables
);
parameter ADDR = 2'b00;
reg [ 7:0] pages [0:1]; // 2 pages for each map - switched by pent1m_ROM
reg [ 1:0] ramnrom; // ram(=1) or rom(=0)
reg [ 1:0] dos_7ffd; // =1 7ffd bits (ram) or DOS enter mode (rom) for given page
reg [ 1:0] wrdisables; // for each map
reg mreq_n_reg, rd_n_reg, m1_n_reg;
wire dos_exec_stb, ram_exec_stb;
reg [2:0] stall_count;
// output data for port xxBE
assign rd_page0 = pages[0];
assign rd_page1 = pages[1];
//
assign rd_dos7ffd = dos_7ffd;
assign rd_ramnrom = ramnrom;
assign rd_wrdisables = wrdisables;
// paging function, does not set pages, ramnrom, dos_7ffd
//
always @(posedge fclk)
begin
if( pager_off )
begin // atm no pager mode - each window has same ROM
romnram <= 1'b1;
page <= 8'hFF;
wrdisable <= 1'b0;
end
else // pager on
begin
if( (ADDR==2'b00) && (pent1m_ram0_0 || in_nmi || in_trdemu) )
begin
wrdisable <= 1'b0;
if( in_nmi || in_trdemu )
begin
romnram <= 1'b0;
page <= { 7'h7F, in_nmi };
end
else // if( pent1m_ram0_0 )
begin
romnram <= 1'b0;
page <= 8'd0;
end
end
else
begin
wrdisable <= wrdisables[ pent1m_ROM ];
romnram <= ~ramnrom[ pent1m_ROM ];
if( dos_7ffd[ pent1m_ROM ] ) // 7ffd memmap switching
begin
if( ramnrom[ pent1m_ROM ] )
begin // ram map
if( pent1m_1m_on )
begin // map whole Mb from 7ffd to atm pages
page <= { pages[ pent1m_ROM ][7:6], pent1m_page[5:0] };
end
else //128k like in atm2
begin
page <= { pages[ pent1m_ROM ][7:3], pent1m_page[2:0] };
end
end
else // rom map with dos
begin
page <= { pages[ pent1m_ROM ][7:1], dos };
end
end
else // no 7ffd impact
begin
page <= pages[ pent1m_ROM ];
end
end
end
end
// port reading: sets pages, ramnrom, dos_7ffd
//
always @(posedge fclk, negedge rst_n)
if( !rst_n )
begin
wrdisables <= 2'b00;
end
else if( atmF7_wr )
begin
if( za[15:14]==ADDR )
case( {za[11],za[10]} )
2'b10: begin // xxBF7 port -- ROM/RAM readonly bit
wrdisables[ pent1m_ROM ] <= zd[0];
end
default: begin
// nothing
end
endcase
end
//
always @(posedge fclk)
if( atmF7_wr )
begin
if( za[15:14]==ADDR )
case( {za[11],za[10]} )
2'b11: begin // xFF7 port
pages [ pent1m_ROM ] <= ~{ 2'b11, zd[5:0] };
ramnrom [ pent1m_ROM ] <= zd[6];
dos_7ffd[ pent1m_ROM ] <= zd[7];
end
2'b01: begin // x7F7 port
pages [ pent1m_ROM ] <= ~zd;
ramnrom [ pent1m_ROM ] <= 1'b1; // RAM on
// dos_7ffd - UNCHANGED!!! (possibility to use 7ffd 1m and 128k addressing in the whole 4m!)
end
default: begin
// nothing
end
endcase
end
// DOS turn on/turn off
//
`ifdef SIMULATE
initial
begin
m1_n_reg = 1'b1;
mreq_n_reg = 1'b1;
rd_n_reg = 1'b1;
stall_count = 3'b000;
end
`endif
always @(posedge fclk) if( zpos )
begin
m1_n_reg <= m1_n;
end
always @(posedge fclk) if( zneg )
begin
mreq_n_reg <= mreq_n;
end
assign dos_exec_stb = zneg && (za[15:14]==ADDR) &&
(!m1_n_reg) && (!mreq_n) && mreq_n_reg &&
(za[13:8]==6'h3D) &&
dos_7ffd[1'b1] && (!ramnrom[1'b1]) && pent1m_ROM;
assign ram_exec_stb = zneg && (za[15:14]==ADDR) &&
(!m1_n_reg) && (!mreq_n) && mreq_n_reg &&
ramnrom[pent1m_ROM];
assign dos_turn_on = dos_exec_stb;
assign dos_turn_off = ram_exec_stb;
// stall Z80 for some time when dos turning on to allow ROM chip to supply new data
// this can be important at 7 or even 14 mhz. minimum stall time is
// 3 clocks @ 28 MHz
always @(posedge fclk)
begin
// переключение в ДОС пзу происходит за полтакта z80 до того, как
// z80 считает данные. т.е. у пзу полтакта для выдачи новых данных.
// 3.5мгц - 140 нан, 7мгц - 70 нан, 14мгц - 35 нан.
// для пзухи 120нс на 14мгц надо еще 3 полтакта добавить, или другими
// словами, добавить к любой задержке на любой частоте минимум 3 такта
// 28 мгц.
if( dos_turn_on )
begin
stall_count[2] <= 1'b1; // count: 000(stop) -> 101 -> 110 -> 111 -> 000(stop)
stall_count[0] <= 1'b1;
end
else if( stall_count[2] )
begin
stall_count[2:0] <= stall_count[2:0] + 3'd1;
end
end
assign zclk_stall = dos_turn_on | stall_count[2];
endmodule