// ZX-Evo Base Configuration (c) NedoPC 2008,2009,2010,2011,2012,2013,2014
//
// generates horizontal sync, blank and video start strobe, horizontal window
/*
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/>.
*/
//
// =\ /=========||...
// ==\ /==========||...
// ====--- -------===========||...
// | \ / | |
// | --- | |
// | | | | |
// 0 t1 | t3 t4
// t2
// at 0, video ends and blank begins
// t1 = 10 clocks (@7MHz), sync begins
// t2-t1 = 33 clocks
// t3-t2 = 41 clocks, then video starts
//
// repetition period = 448 clocks
`include "../include/tune.v"
module video_sync_h(
input wire clk,
input wire init, // one-pulse strobe read at cend==1, initializes phase
// this is mainly for phasing with CPU clock 3.5/7 MHz
// still not used, but this may change anytime
input wire cend, // working strobes from DRAM controller (7MHz)
input wire pre_cend,
// modes inputs
input wire mode_atm_n_pent,
input wire mode_a_text,
output reg hblank,
output reg hsync,
output reg line_start, // 1 video cycle prior to actual start of visible line
output reg hsync_start, // 1 cycle prior to beginning of hsync: used in frame sync/blank generation
// these signals coincide with cend
output reg hint_start, // horizontal position of INT start, for fine tuning
output reg scanin_start,
output reg hpix, // marks gate during which pixels are outting
// these signals turn on and turn off 'go' signal
output reg fetch_start, // 18 cycles earlier than hpix, coincide with cend
output reg fetch_end // --//--
);
localparam HBLNK_BEG = 9'd00;
localparam HSYNC_BEG = 9'd10;
localparam HSYNC_END = 9'd43;
localparam HBLNK_END = 9'd88;
// pentagon (x256)
localparam HPIX_BEG_PENT = 9'd140; // 52 cycles from line_start to pixels beginning
localparam HPIX_END_PENT = 9'd396;
// atm (x320)
localparam HPIX_BEG_ATM = 9'd108; // 52 cycles from line_start to pixels beginning
localparam HPIX_END_ATM = 9'd428;
localparam FETCH_FOREGO = 9'd18; // consistent with older go_start in older fetch.v:
// actual data starts fetching 2 dram cycles after
// 'go' goes to 1, screen output starts another
// 16 cycles after 1st data bundle is fetched
localparam SCANIN_BEG = 9'd88; // when scan-doubler starts pixel storing
localparam HINT_BEG = 9'd2;
localparam HPERIOD = 9'd448;
reg [8:0] hcount;
// for simulation only
//
initial
begin
hcount = 9'd0;
hblank = 1'b0;
hsync = 1'b0;
line_start = 1'b0;
hsync_start = 1'b0;
hpix = 1'b0;
end
always @(posedge clk) if( cend )
begin
if( init || (hcount==(HPERIOD-9'd1)) )
hcount <= 9'd0;
else
hcount <= hcount + 9'd1;
end
always @(posedge clk) if( cend )
begin
if( hcount==HBLNK_BEG )
hblank <= 1'b1;
else if( hcount==HBLNK_END )
hblank <= 1'b0;
if( hcount==HSYNC_BEG )
hsync <= 1'b1;
else if( hcount==HSYNC_END )
hsync <= 1'b0;
end
always @(posedge clk)
begin
if( pre_cend )
begin
if( hcount==HSYNC_BEG )
hsync_start <= 1'b1;
if( hcount==HBLNK_END )
line_start <= 1'b1;
if( hcount==SCANIN_BEG )
scanin_start <= 1'b1;
end
else
begin
hsync_start <= 1'b0;
line_start <= 1'b0;
scanin_start <= 1'b0;
end
end
wire fetch_start_time, fetch_start_condition;
wire fetch_end_condition;
reg [3:0] fetch_start_wait;
assign fetch_start_time = (mode_atm_n_pent ?
(HPIX_BEG_ATM -FETCH_FOREGO-9'd4) :
(HPIX_BEG_PENT-FETCH_FOREGO-9'd4) ) == hcount;
always @(posedge clk) if( cend )
fetch_start_wait[3:0] <= { fetch_start_wait[2:0], fetch_start_time };
assign fetch_start_condition = mode_a_text ? fetch_start_time : fetch_start_wait[3];
always @(posedge clk)
if( pre_cend && fetch_start_condition )
fetch_start <= 1'b1;
else
fetch_start <= 1'b0;
assign fetch_end_time = (mode_atm_n_pent ?
(HPIX_END_ATM -FETCH_FOREGO) :
(HPIX_END_PENT-FETCH_FOREGO) ) == hcount;
always @(posedge clk)
if( pre_cend && fetch_end_time )
fetch_end <= 1'b1;
else
fetch_end <= 1'b0;
always @(posedge clk)
begin
if( pre_cend && (hcount==HINT_BEG) )
hint_start <= 1'b1;
else
hint_start <= 1'b0;
end
always @(posedge clk) if( cend )
begin
if( hcount==(mode_atm_n_pent ? HPIX_BEG_ATM : HPIX_BEG_PENT) )
hpix <= 1'b1;
else if( hcount==(mode_atm_n_pent ? HPIX_END_ATM : HPIX_END_PENT) )
hpix <= 1'b0;
end
endmodule