[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!

svn path=/branches/ros-amd64-bringup/; revision=43770

reactos/drivers/base/kddll/kdcom.c

@@ -216,6 +216,11 @@ KdpSendByte(IN BYTE Byte)
     /* 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 @@ KDP_STATUS
 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))
     {