x86: Disable NMI while initializing RTC

According to [1], we should disable non-maskable and maskable interrupts
while initializing RTC. Otherwise, the RTC may be left in an undefined
state (non-functional) if an interrupt occurs. Currently, maskable
interrupts are already disabled, but NMI is not.

This patch adds helpers APIs to enable/disable non-maskable interrupts
(NMI) and changes rtc_init() to disable NMI while initializing the RTC.

NMI enable/disable code is legacy-PC specific therefore it was put in
driver/legacy_pc/ directory.

Regarding the RTC initialization changes, just calling nmi_disable() and
nmi_enable is not enough since NMI and RTC share the same IO port. So We
should also set the NMI_ENABLE bit while selecting the RTC_INDEX.

Additionally, the nmi_disable() call is not strictly required since we
set the NMI_ENABLE bit while selecting the RTC_INDEX. However, to make
clear hat we are disabling NMI and to improve readability (by matching
NMI disable/enable), the nmi_disable() call was purposely used.

[1] http://wiki.osdev.org/RTC

cpu/x86/Makefile.x86_quarkX1000

@@ -2,6 +2,6 @@ include $(CONTIKI)/cpu/x86/Makefile.x86_common
 
 CONTIKI_CPU_DIRS += drivers/legacy_pc init/legacy_pc
 
-CONTIKI_SOURCEFILES += bootstrap_quarkX1000.S rtc.c pit.c pic.c irq.c
+CONTIKI_SOURCEFILES += bootstrap_quarkX1000.S rtc.c pit.c pic.c irq.c nmi.c
 
 LINKERSCRIPT = $(CONTIKI)/cpu/x86/quarkX1000.ld

cpu/x86/drivers/legacy_pc/nmi.c

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2015, Intel Corporation. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "helpers.h"
+
+#define NMI_ENABLE_PORT 0x70
+
+void
+nmi_enable(void)
+{
+  uint8_t value = inb(NMI_ENABLE_PORT);
+  outb(NMI_ENABLE_PORT, value & ~BIT(8));
+}
+/*---------------------------------------------------------------------------*/
+void
+nmi_disable(void)
+{
+  uint8_t value = inb(NMI_ENABLE_PORT);
+  outb(NMI_ENABLE_PORT, value | BIT(8));
+}

cpu/x86/drivers/legacy_pc/nmi.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2015, Intel Corporation. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef NMI_H
+#define NMI_H
+
+void nmi_enable(void);
+
+void nmi_disable(void);
+
+#endif /* NMI_H */

cpu/x86/drivers/legacy_pc/rtc.c

@@ -30,6 +30,7 @@
 
 #include "drivers/legacy_pc/rtc.h"
 #include "drivers/legacy_pc/pic.h"
+#include "drivers/legacy_pc/nmi.h"
 #include "helpers.h"
 #include "interrupt.h"
 
@@ -72,19 +73,23 @@ rtc_init(rtc_frequency_t frequency, void (*callback)(void))
 
   SET_INTERRUPT_HANDLER(RTC_INT, 0, rtc_handler);
 
+  nmi_disable();
+
   /* Select interrupt period to 7.8125 ms */
-  outb(RTC_INDEX_REGISTER, 0x0A);
+  outb(RTC_INDEX_REGISTER, 0x8A);
   reg_a = inb(RTC_TARGET_REGISTER);
   reg_a &= 0xF0;
   reg_a |= frequency;
-  outb(RTC_INDEX_REGISTER, 0x0A);
+  outb(RTC_INDEX_REGISTER, 0x8A);
   outb(RTC_TARGET_REGISTER, reg_a);
 
   /* Enable periodic interrupt */
-  outb(RTC_INDEX_REGISTER, 0x0B);
+  outb(RTC_INDEX_REGISTER, 0x8B);
   reg_b = inb(RTC_TARGET_REGISTER);
-  outb(RTC_INDEX_REGISTER, 0x0B);
+  outb(RTC_INDEX_REGISTER, 0x8B);
   outb(RTC_TARGET_REGISTER, reg_b | BIT(6));
 
+  nmi_enable();
+
   pic_unmask_irq(RTC_IRQ);
 }