[tkreuzer] 43770: [KDCOM] For unknown reasons it's not enough to check LSR if the port is ready to receive or not. Adding additional port reads improves the reliability of the data massively. Now it's possible to use kdcom on windows XP!

Author: tkreuzer
Date: Mon Oct 26 04:24:03 2009
New Revision: 43770

URL: http://svn.reactos.org/svn/reactos?rev=43770&view=rev
Log:
[KDCOM]
For unknown reasons it's not enough to check LSR if the port is ready to receive or
not. Adding additional port reads improves the reliability of the data massively. Now
it's possible to use kdcom on windows XP!

Modified:
    branches/ros-amd64-bringup/reactos/drivers/base/kddll/kdcom.c

Modified: branches/ros-amd64-bringup/reactos/drivers/base/kddll/kdcom.c
URL:
http://svn.reactos.org/svn/reactos/branches/ros-amd64-bringup/reactos/drive…
==============================================================================
--- branches/ros-amd64-bringup/reactos/drivers/base/kddll/kdcom.c [iso-8859-1] (original)
+++ branches/ros-amd64-bringup/reactos/drivers/base/kddll/kdcom.c [iso-8859-1] Mon Oct 26
04:24:03 2009
@@ -216,6 +216,11 @@
     /* Wait for the port to be ready */
     while ((READ_PORT_UCHAR(ComPortBase + COM_LSR) & LSR_TBE) == 0);
 
+    /* This is needed due to subtle timing issues */
+    READ_PORT_UCHAR(ComPortBase + COM_MSR);
+    while ((READ_PORT_UCHAR(ComPortBase + COM_LSR) & LSR_TBE) == 0);
+    READ_PORT_UCHAR(ComPortBase + COM_MSR);
+
     /* Send the byte */
     WRITE_PORT_UCHAR(ComPortBase + COM_DAT, Byte);
 }
@@ -224,6 +229,8 @@
 NTAPI
 KdpPollByte(OUT PBYTE OutByte)
 {
+    READ_PORT_UCHAR(ComPortBase + COM_MSR); // Timing
+
     /* Check if data is available */
     if ((READ_PORT_UCHAR(ComPortBase + COM_LSR) & LSR_DR))
     {