diff --git a/arch/hc/include/hcs12/irq.h b/arch/hc/include/hcs12/irq.h
index 22e9dd6b4d..cb3eb8ecbb 100755
--- a/arch/hc/include/hcs12/irq.h
+++ b/arch/hc/include/hcs12/irq.h
@@ -50,6 +50,17 @@
 /************************************************************************************
  * Definitions
  ************************************************************************************/
+/* CCR bit definitions */
+
+#define HCS12_CCR_C (1 << 0) /* Bit 0: Carry/Borrow status bit */
+#define HCS12_CCR_V (1 << 1) /* Bit 1: Two’s complement overflow status bit */
+#define HCS12_CCR_Z (1 << 2) /* Bit 2: Zero status bit */
+#define HCS12_CCR_N (1 << 3) /* Bit 3: Negative status bit */
+#define HCS12_CCR_I (1 << 4) /* Bit 4: Maskable interrupt control bit */
+#define HCS12_CCR_H (1 << 5) /* Bit 5: Half-carry status bit */
+#define HCS12_CCR_X (1 << 6) /* Bit 6: Non-maskable interrupt control bit */
+#define HCS12_CCR_S (1 << 7) /* Bit 7: STOP instruction control bit */
+
 /************************************************************************************
  *	Register state save strucure
  *   Low Address        <-- SP after state save
@@ -167,25 +178,72 @@ struct xcptcontext
  * Inline functions
  ****************************************************************************/
 
+/* Enable/Disable interrupts */
+
+#define ienable()  __asm("cli");
+#define idisable() __asm("orcc #0x10")
+#define xenable()  __asm("andcc #0xbf")
+#define xdisable() __asm("orcc #0x40")
+
+/* Get the current value of the stack pointer */
+
+static inline uint16_t up_getsp(void)
+{
+  uint16_t ret;
+  __asm__
+  (
+    "\tsts %0\n"
+	: "=m"(ret) :
+  );
+  return ret;
+}
+
+/* Get the current value of the CCR */
+
+static inline irqstate_t up_getccr(void)
+{
+  irqstate_t ccr;
+  __asm__
+  (
+    "\ttpa\n"
+    "\tstaa %0\n"
+	: "=m"(ccr) :
+  );
+  return ccr;
+}
+
 /* Save the current interrupt enable state & disable IRQs */
 
 static inline irqstate_t irqsave(void)
 {
-  /* To be provided */
+  irqstate_t ccr;
+  __asm__
+  (
+    "\ttpa\n"
+    "\tstaa %0\n"
+    "\torcc #0x50\n"
+	: "=m"(ccr) :
+  );
+  return ccr;
 }
 
-/* Restore saved IRQ & FIQ state */
+/* Restore saved interrupt state */
 
 static inline void irqrestore(irqstate_t flags)
 {
-  /* To be provided */
+  /* Should interrupts be enabled? */
+
+  if ((flags & HCS12_CCR_I) == 0)
+    {
+      /* Yes.. unmask I- and Z-interrupts */
+
+      __asm("andcc #0xaf");
+    }
 }
 
-static inline void system_call(swint_t func, int parm1,
-                               int parm2, int parm3)
-{
-  /* To be provided */
-}
+/* System call */
+
+#define system_call(f,p1,p2,p3) __asm("swi")
 
 /************************************************************************************
  * Public Data
diff --git a/arch/hc/include/hcs12/types.h b/arch/hc/include/hcs12/types.h
index 33008793a6..71b311fb79 100755
--- a/arch/hc/include/hcs12/types.h
+++ b/arch/hc/include/hcs12/types.h
@@ -93,7 +93,7 @@ typedef unsigned short     _uintptr_t;
 
 /* This is the size of the interrupt state save returned by irqsave()*/
 
-typedef unsigned int       irqstate_t;
+typedef unsigned char      irqstate_t;
 
 #endif /* __ASSEMBLY__ */
 
diff --git a/arch/hc/src/common/up_doirq.c b/arch/hc/src/common/up_doirq.c
index d3de013fa0..05dbaa2cf3 100644
--- a/arch/hc/src/common/up_doirq.c
+++ b/arch/hc/src/common/up_doirq.c
@@ -89,10 +89,6 @@ uint8_t *up_doirq(int irq, uint8_t *regs)
   DEBUGASSERT(current_regs == NULL);
   current_regs = regs;
 
-  /* Mask and acknowledge the interrupt */
-
-  up_maskack_irq(irq);
-
   /* Deliver the IRQ */
 
   irq_dispatch(irq, regs);
@@ -108,10 +104,6 @@ uint8_t *up_doirq(int irq, uint8_t *regs)
   /* Indicate that we are no long in an interrupt handler */
 
   current_regs = NULL;
-
-  /* Unmask the last interrupt (global interrupts are still disabled) */
-
-  up_enable_irq(irq);
 #endif
   up_ledoff(LED_INIRQ);
   return regs;
diff --git a/arch/hc/src/m9s12/m9s12_assert.c b/arch/hc/src/m9s12/m9s12_assert.c
index 7b167d1837..97d18b64f6 100644
--- a/arch/hc/src/m9s12/m9s12_assert.c
+++ b/arch/hc/src/m9s12/m9s12_assert.c
@@ -86,23 +86,6 @@
  * Private Functions
  ****************************************************************************/
 
-/****************************************************************************
- * Name: up_getsp
- ****************************************************************************/
-
-/* I don't know if the builtin to get SP is enabled */
-
-static inline uint16_t up_getsp(void)
-{
-  uint16_t spval;
-  __asm__
-  (
-    "\tsts spval\n"
-	: "=A"(spval) :
-  );
-  return spval;
-}
-
 /****************************************************************************
  * Name: up_stackdump
  ****************************************************************************/
diff --git a/arch/hc/src/m9s12/m9s12_initialstate.c b/arch/hc/src/m9s12/m9s12_initialstate.c
index 7efe779420..c537546b1e 100644
--- a/arch/hc/src/m9s12/m9s12_initialstate.c
+++ b/arch/hc/src/m9s12/m9s12_initialstate.c
@@ -113,9 +113,13 @@ void up_initial_state(_TCB *tcb)
    */
 
 # ifdef CONFIG_SUPPRESS_INTERRUPTS
-  xcp->regs[REG_CCR]      = 0xd0;  /* Disable STOP, Mask I- and Z- interrupts */
+  /* Disable STOP, Mask I- and Z- interrupts */
+
+  xcp->regs[REG_CCR]      = HCS12_CCR_S|HCS12_CCR_X|HCS12_CCR_I;  
 # else
-  xcp->regs[REG_CCR]      = 0x80;  /* Disable STOP, Enable I- and Z-interrupts */
+  /* Disable STOP, Enable I- and Z-interrupts */
+
+  xcp->regs[REG_CCR]      = HCS12_CCR_S;
 # endif
 }
 
diff --git a/arch/hc/src/m9s12/m9s12_irq.c b/arch/hc/src/m9s12/m9s12_irq.c
index 20a86e1efc..1fb59d5511 100755
--- a/arch/hc/src/m9s12/m9s12_irq.c
+++ b/arch/hc/src/m9s12/m9s12_irq.c
@@ -80,50 +80,7 @@ uint8_t *current_regs;
 
 void up_irqinitialize(void)
 {
-  /* Disable all interrupts */
-#warning "Missing Logic"
-
   /* currents_regs is non-NULL only while processing an interrupt */
 
   current_regs = NULL;
-
-}
-
-/****************************************************************************
- * Name: up_disable_irq
- *
- * Description:
- *   Disable the IRQ specified by 'irq'
- *
- ****************************************************************************/
-
-void up_disable_irq(int irq)
-{
-#warning "Missing Logic"
-}
-
-/****************************************************************************
- * Name: up_enable_irq
- *
- * Description:
- *   Enable the IRQ specified by 'irq'
- *
- ****************************************************************************/
-
-void up_enable_irq(int irq)
-{
-#warning "Missing Logic"
-}
-
-/****************************************************************************
- * Name: up_maskack_irq
- *
- * Description:
- *   Mask the IRQ and acknowledge it
- *
- ****************************************************************************/
-
-void up_maskack_irq(int irq)
-{
-#warning "Missing Logic"
 }
diff --git a/arch/hc/src/m9s12/m9s12_serial.c b/arch/hc/src/m9s12/m9s12_serial.c
index 6d60ee9bcf..7b5ba365ed 100755
--- a/arch/hc/src/m9s12/m9s12_serial.c
+++ b/arch/hc/src/m9s12/m9s12_serial.c
@@ -331,7 +331,9 @@ static int up_setup(struct uart_dev_s *dev)
   struct up_dev_s *priv = (struct up_dev_s*)dev->priv;
 #ifndef CONFIG_SUPPRESS_SCI_CONFIG
   uint8_t cr1;
+#endif
 
+#ifndef CONFIG_SUPPRESS_SCI_CONFIG
   /* Calculate the BAUD divisor */
 
   tmp = SCIBR_VALUE(priv->baud);
@@ -371,17 +373,12 @@ static int up_setup(struct uart_dev_s *dev)
   up_serialout(priv, HCS12_SCI_CR1_OFFSET, cr1);
 #endif
 
-  /* Enable Rx interrupts from the SCI.  We don't want Tx interrupts until we
-   * have something to send.  We will check for serial errors as part of Rx
-   * interrupt processing.  Interrupts won't be fully enabled until the
-   * interrupt vector is attached.
+  /* Enable Rx and Tx, keeping all interrupts disabled. We don't want
+   * interrupts until the interrupt vector is attached.
    */
 
-  priv->im = SCI_CR2_RIE;
-
-  /* Enable Rx and Tx */
-
-  up_serialout(priv, HCS12_SCI_CR2_OFFSET, (SCI_CR2_RIE|SCI_CR2_TE|SCI_CR2_RE));
+  priv->im = 0;
+  up_serialout(priv, HCS12_SCI_CR2_OFFSET, (SCI_CR2_TE|SCI_CR2_RE));
   return OK;
 }
 
@@ -424,11 +421,12 @@ static int up_attach(struct uart_dev_s *dev)
   ret = irq_attach(priv->irq, up_interrupt);
   if (ret == OK)
     {
-       /* Enable the interrupt (RX and TX interrupts are still disabled
-        * in the SCI
+       /* Enable the Rx interrupt (the TX interrupt is still disabled
+        * until we have something to send). 
         */
 
-       up_enable_irq(priv->irq);
+       priv->im = SCI_CR2_RIE;
+       up_setsciint(priv);
     }
   return ret;
 }
@@ -446,7 +444,7 @@ static int up_attach(struct uart_dev_s *dev)
 static void up_detach(struct uart_dev_s *dev)
 {
   struct up_dev_s *priv = (struct up_dev_s*)dev->priv;
-  up_disable_irq(priv->irq);
+  up_disablesciint(priv, NULL);
   irq_detach(priv->irq);
 }
 
diff --git a/arch/hc/src/m9s12/m9s12_timerisr.c b/arch/hc/src/m9s12/m9s12_timerisr.c
index 3839badf20..22e76d7ee6 100755
--- a/arch/hc/src/m9s12/m9s12_timerisr.c
+++ b/arch/hc/src/m9s12/m9s12_timerisr.c
@@ -182,8 +182,4 @@ void up_timerinit(void)
   regval  = getreg8(HCS12_CRG_CRGINT);
   regval |= CRG_CRGINT_RTIE;
   putreg8(regval, HCS12_CRG_CRGINT);
-
-  /* And enable the timer interrupt */
-
-  up_enable_irq(HCS12_IRQ_VRTI);
 }
diff --git a/configs/demo9s12ne64/ostest/defconfig b/configs/demo9s12ne64/ostest/defconfig
index fc52adf261..9c2afdf33a 100755
--- a/configs/demo9s12ne64/ostest/defconfig
+++ b/configs/demo9s12ne64/ostest/defconfig
@@ -52,6 +52,9 @@
 # CONFIG_DRAM_SIZE - Describes the installed RAM.
 # CONFIG_DRAM_START - The start address of RAM (physical)
 # CONFIG_DRAM_END - Last address+1 of installed RAM
+# CONFIG_ARCH_NOINTC - define if the architecture does not
+#   support an interrupt controller or otherwise cannot support
+#   APIs like up_enable_irq() and up_disable_irq().
 # CONFIG_ARCH_IRQPRIO - The ST32F103Z supports interrupt prioritization
 # CONFIG_ARCH_INTERRUPTSTACK - This architecture supports an interrupt
 #   stack. If defined, this symbol is the size of the interrupt
@@ -80,6 +83,7 @@ CONFIG_BOARD_LOOPSPERMSEC=5483
 CONFIG_DRAM_SIZE=0x00010000
 CONFIG_DRAM_START=0x20000000
 CONFIG_DRAM_END=(CONFIG_DRAM_START+CONFIG_DRAM_SIZE)
+CONFIG_ARCH_NOINTC=y
 CONFIG_ARCH_IRQPRIO=n
 CONFIG_ARCH_INTERRUPTSTACK=n
 CONFIG_ARCH_STACKDUMP=y