Fix race condition in Bconout()

This applies to all functions that implement Bconout(): bconout1(),
bconoutTT(), bconoutA(), bconoutB().  There was a small window
between checking for the register on the device being empty, and
putting the data into the iorec buffer if it wasn't.  If the device
became empty in that window, the transmit interrupt would trigger
but the interrupt wouldn't see any data in the buffer at that point,
and the data could be stuck in the iorec buffer.
Thanks to Christian Zietz for pointing this out.

bios/serport.c

@@ -157,19 +157,13 @@ static WORD incr_tail(IOREC *iorec)
 #if (!CONF_WITH_COLDFIRE_RS232 && CONF_WITH_MFP_RS232 && !RS232_DEBUG_PRINT) || CONF_WITH_TT_MFP || CONF_WITH_SCC
 static void put_iorecbuf(IOREC *out, WORD b)
 {
-    WORD old_sr, tail;
-
-    /* disable interrupts */
-    old_sr = set_sr(0x2700);
+    WORD tail;
 
     *(out->buf + out->tail) = (UBYTE)b;
     tail = incr_tail(out);
     if (tail != out->head) {        /* buffer not full,  */
         out->tail = tail;           /*  so ok to advance */
     }
-
-    /* restore interrupts */
-    set_sr(old_sr);
 }
 #endif
 
@@ -294,6 +288,10 @@ LONG bcostat1(void)
 
 LONG bconout1(WORD dev, WORD b)
 {
+    WORD old_sr;
+
+    MAYBE_UNUSED(old_sr);
+
     /* Wait for transmit buffer to become empty */
     while(!bcostat1())
         ;
@@ -306,6 +304,9 @@ LONG bconout1(WORD dev, WORD b)
     MFP_BASE->udr = (char)b;
     return 1L;
 # else
+    /* disable interrupts */
+    old_sr = set_sr(0x2700);
+
     /*
      * If the buffer is empty & the port is empty, output directly.
      * otherwise queue the data.
@@ -315,6 +316,10 @@ LONG bconout1(WORD dev, WORD b)
     } else {
         put_iorecbuf(&iorec1.out, b);
     }
+
+    /* restore interrupts */
+    set_sr(old_sr);
+
     return 1L;
 # endif
 #else
@@ -412,9 +417,15 @@ static LONG bcostatTT(void)
 
 static LONG bconoutTT(WORD dev, WORD b)
 {
+    WORD old_sr;
+
     /* Wait for transmit buffer to become empty */
     while(!bcostatTT())
         ;
+
+    /* disable interrupts */
+    old_sr = set_sr(0x2700);
+
      /*
      * If the buffer is empty & the port is empty, output directly.
      * otherwise queue the data.
@@ -424,6 +435,10 @@ static LONG bconoutTT(WORD dev, WORD b)
     } else {
         put_iorecbuf(&iorecTT.out, b);
     }
+
+    /* restore interrupts */
+    set_sr(old_sr);
+
     return 1L;
 }
 
@@ -503,11 +518,15 @@ static LONG bconoutA(WORD dev, WORD b)
 {
     SCC *scc = (SCC *)SCC_BASE;
     IOREC *out;
+    WORD old_sr;
 
     /* Wait for transmit buffer to become available */
     while(!bcostatA())
         ;
 
+    /* disable interrupts */
+    old_sr = set_sr(0x2700);
+
      /*
      * If the buffer is empty & the port is empty, output directly.
      * otherwise queue the data.
@@ -520,6 +539,9 @@ static LONG bconoutA(WORD dev, WORD b)
         put_iorecbuf(out, b);
     }
 
+    /* restore interrupts */
+    set_sr(old_sr);
+
     return 1L;
 }
 
@@ -564,8 +586,10 @@ LONG bconoutB(WORD dev, WORD b)
 {
     SCC *scc = (SCC *)SCC_BASE;
     IOREC *out;
+    WORD old_sr;
 
     MAYBE_UNUSED(out);
+    MAYBE_UNUSED(old_sr);
 
     while(!bcostatB())
         ;
@@ -574,6 +598,9 @@ LONG bconoutB(WORD dev, WORD b)
     scc->portB.data = (UBYTE)b;
     RECOVERY_DELAY;
 #else
+    /* disable interrupts */
+    old_sr = set_sr(0x2700);
+
     /*
      * If the buffer is empty & the port is empty, output directly.
      * otherwise queue the data.
@@ -585,6 +612,9 @@ LONG bconoutB(WORD dev, WORD b)
     } else {
         put_iorecbuf(out, b);
     }
+
+    /* restore interrupts */
+    set_sr(old_sr);
 #endif
 
     return 1L;