x86: Add pic_unmask_irq() helper

This patch implements the pic_unmask_irq() helper and uses it where
applicable. This function zeros the corresponding bit from the IRQ
number in IMR register.

This patch doesn't implement the pic_mask_irq() helper since it is not
useful at this moment.

cpu/x86/Makefile.x86

@@ -1,6 +1,6 @@
 CONTIKI_CPU_DIRS = . drivers
 
-CONTIKI_SOURCEFILES += mtarch.c gdt.c helpers.S idt.c cpu.c rtc.c pit.c
+CONTIKI_SOURCEFILES += mtarch.c gdt.c helpers.S idt.c cpu.c rtc.c pit.c pic.c
 
 ### Compiler definitions
 CC       = gcc

cpu/x86/drivers/pic.c

@@ -0,0 +1,48 @@
+/*
+ * 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 "drivers/pic.h"
+
+void
+pic_unmask_irq(unsigned int num)
+{
+  uint16_t port;
+  uint8_t bitmap;
+
+  if(num <= 7) {
+    port = PIC1_DATA_PORT;
+  } else {
+    port = PIC2_DATA_PORT;
+    num -= 8;
+  }
+
+  bitmap = inb(port);
+  outb(port, bitmap & ~BIT(num));
+}

cpu/x86/drivers/pic.h

@@ -38,6 +38,8 @@
 #define PIC2_CMD_PORT   0xA0
 #define PIC2_DATA_PORT  0xA1
 
+void pic_unmask_irq(unsigned int num);
+
 /* This function initializes the daisy-chained Master and Slave 8259 PICs.
  * It is only called once, so let's give the compiler the option to inline it.
  * For more information about the ICWs, please refer to http://stanislavs.org/helppc/8259.html.

cpu/x86/drivers/pit.c

@@ -30,6 +30,7 @@
 
 #include <math.h>
 
+#include "drivers/pic.h"
 #include "pit.h"
 #include "helpers.h"
 #include "interrupt.h"
@@ -75,6 +76,5 @@ pit_init(uint32_t ticks_rate, pit_int_callback cb)
   outb(PIT_COUNTER0_PORT, divisor & 0xFF); /* Write least significant bytes first. */
   outb(PIT_COUNTER0_PORT, (divisor >> 8) & 0xFF);
 
-  /* FIXME: Unmask IRQ0 from Master PIC. Add a pic_set_mask() or similar and call it here. */
-  outb(0x21, 0xfa);
+  pic_unmask_irq(0);
 }

cpu/x86/drivers/rtc.c

@@ -29,6 +29,7 @@
  */
 
 #include "drivers/rtc.h"
+#include "drivers/pic.h"
 #include "helpers.h"
 #include "interrupt.h"
 
@@ -87,6 +88,5 @@ rtc_init(rtc_frequency_t frequency, void (*callback)(void))
   outb(RTC_INDEX_REGISTER, 0x0B);
   outb(RTC_TARGET_REGISTER, reg_b | BIT(6));
 
-  /* Unmask IRQ8 */
-  outb(0xA1, 0xFE);
+  pic_unmask_irq(8);
 }