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Implement screen disable / blanking

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Ernest Wong 2018-01-15 18:25:14 +13:00 committed by Fabian
parent 3c72863846
commit 81018ce07b
1 changed files with 33 additions and 1 deletions
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34
src/vga.js
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@ -261,6 +261,7 @@ function VGAScreen(cpu, bus, vga_memory_size)
this.dac_map = new Uint8Array(0x10);
this.attribute_controller_index = -1;
this.palette_source = 0x20;
this.attribute_mode = 0;
this.color_plane_enable = 0;
this.horizontal_panning = 0;
@ -271,6 +272,7 @@ function VGAScreen(cpu, bus, vga_memory_size)
// bitmap of planes 0-3
this.plane_write_bm = 0xF;
this.sequencer_memory_mode = 0;
this.clocking_mode = 0;
this.graphics_index = -1;
this.plane_read = 0, // value 0-3, which plane to read
@ -1262,12 +1264,22 @@ VGAScreen.prototype.update_vga_panning = function()
{
this.text_mode_redraw();
}
if(this.svga_enabled || !this.virtual_width || !this.svga_width)
{
// Skip for svga mode and avoid division by zero
return;
}
if(!this.palette_source || (this.clocking_mode & 0x20))
{
// Palette source and screen disable bits = draw nothing
// See http://www.phatcode.net/res/224/files/html/ch29/29-05.html#Heading6
// and http://www.osdever.net/FreeVGA/vga/seqreg.htm#01
this.bus.send("screen-update-layers", []);
return;
}
var start_addr = this.start_address_latched;
// TODO: merge this with other logic?
@ -1351,6 +1363,14 @@ VGAScreen.prototype.port3C0_write = function(value)
dbg_log("attribute controller index register: " + h(value), LOG_VGA);
this.attribute_controller_index = value & 0x1F;
dbg_log("attribute actual index: " + h(this.attribute_controller_index), LOG_VGA);
if(this.palette_source !== (value & 0x20))
{
// A method of blanking the screen.
// See http://www.phatcode.net/res/224/files/html/ch29/29-05.html#Heading6
this.palette_source = value & 0x20;
this.update_vga_panning();
}
}
else
{
@ -1434,7 +1454,7 @@ VGAScreen.prototype.port3C0_write = function(value)
VGAScreen.prototype.port3C0_read = function()
{
dbg_log("3C0 read", LOG_VGA);
var result = this.attribute_controller_index;
var result = this.attribute_controller_index | this.palette_source;
return result;
};
@ -1500,6 +1520,16 @@ VGAScreen.prototype.port3C5_write = function(value)
{
switch(this.sequencer_index)
{
case 0x01:
dbg_log("clocking mode: " + h(value), LOG_VGA);
var previous_clocking_mode = this.clocking_mode;
this.clocking_mode = value;
if((previous_clocking_mode ^ value) & 0x20)
{
// Screen disable bit modified
this.update_vga_panning();
}
break;
case 0x02:
dbg_log("plane write mask: " + h(value), LOG_VGA);
this.plane_write_bm = value;
@ -1519,6 +1549,8 @@ VGAScreen.prototype.port3C5_read = function()
switch(this.sequencer_index)
{
case 0x01:
return this.clocking_mode;
case 0x02:
return this.plane_write_bm;
case 0x04: