From bd0c65cb911455308c4f7f7010807d5da6ea5ca5 Mon Sep 17 00:00:00 2001
From: Miodrag Milanovic <mmicko@gmail.com>
Date: Mon, 4 Jan 2010 13:05:45 +0000
Subject: [PATCH] [PIT8253] Update PIT counter even if there was no elapsed
 cycles (this only affects fast drivers like at586 in MESS)

---
 src/emu/machine/pit8253.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/src/emu/machine/pit8253.c b/src/emu/machine/pit8253.c
index b3529ec7712..e8ea08eb52a 100644
--- a/src/emu/machine/pit8253.c
+++ b/src/emu/machine/pit8253.c
@@ -266,10 +266,10 @@ static void	simulate2(const device_config *device, struct pit8253_timer *timer,
 		}
 		else
 		{
-			if (elapsed_cycles > 0 && timer->phase == 1)
+			if (elapsed_cycles >= 0 && timer->phase == 1)
 			{
 				/* Counter load cycle */
-				--elapsed_cycles;
+				if (elapsed_cycles > 0) --elapsed_cycles;
 				timer->phase = 2;
 				load_counter_value( device, timer );
 			}
@@ -327,10 +327,10 @@ static void	simulate2(const device_config *device, struct pit8253_timer *timer,
         Gate rising-edge sensitive only.
         Rising edge initiates counting and resets output after next clock. */
 
-		if ( elapsed_cycles > 0 && timer->phase == 1 )
+		if ( elapsed_cycles >= 0 && timer->phase == 1 )
 		{
 			/* Counter load cycle, output goes low */
-			--elapsed_cycles;
+			if (elapsed_cycles > 0) --elapsed_cycles;
 			timer->phase = 2;
 			load_counter_value( device, timer );
 			set_output( device, timer, 0 );
@@ -391,9 +391,9 @@ static void	simulate2(const device_config *device, struct pit8253_timer *timer,
 		}
 		else
 		{
-			if ( elapsed_cycles > 0 && timer->phase == 1 )
+			if ( elapsed_cycles >= 0 && timer->phase == 1 )
 			{
-				--elapsed_cycles;
+				if (elapsed_cycles > 0) --elapsed_cycles;
 				timer->phase = 2;
 				load_counter_value( device, timer );
 			}
@@ -412,10 +412,10 @@ static void	simulate2(const device_config *device, struct pit8253_timer *timer,
 					}
 				}
 
-				if ( elapsed_cycles > 0 && timer->phase == 3 )
+				if ( elapsed_cycles >= 0 && timer->phase == 3 )
 				{
 					/* Reload counter, output goes high */
-					--elapsed_cycles;
+					if (elapsed_cycles > 0) --elapsed_cycles;
 					timer->phase = 2;
 					load_counter_value( device, timer );
 					adjusted_value = adjusted_count( bcd, timer->value );
@@ -468,7 +468,7 @@ static void	simulate2(const device_config *device, struct pit8253_timer *timer,
 		}
 		else
 		{
-			if ( elapsed_cycles > 0 && timer->phase == 1 )
+			if ( elapsed_cycles >= 0 && timer->phase == 1 )
 			{
 				--elapsed_cycles;
 				timer->phase = 2;
@@ -546,7 +546,7 @@ static void	simulate2(const device_config *device, struct pit8253_timer *timer,
 		}
 		else
 		{
-			if (elapsed_cycles > 0 && timer->phase == 1)
+			if (elapsed_cycles >= 0 && timer->phase == 1)
 			{
 				--elapsed_cycles;
 				timer->phase = 2;