x86: Initialize the 8259 PIC

The Programmable Interrupt Controller is a chip responsible for
translating hardware interrupts to system interrupts. When it
receives an Interrupt Request (IRQ), it triggers the appropriate
interrupt line reaching the appropriate IDT gate, following a
previously setup offset.

There are 2 daisy-chained PICs. PIC1 handles IRQs 0-7 and PIC2
handles IRQs 8-15. If no vector offset is set, an IRQ0, for instance,
would trigger the interrupt 0, clashing with the "Division by zero exception"
handler. Thus the IRQs must be remapped.

This patch implements the PICs initialization through their 4
Initialization Command Words (ICWs) in a very "canonical" way:
- ICW1: the initializing command;
- ICW2: the vector offset for the PIC1 and PIC2 (we add an offset of 32 positions);
- ICW3: the inter-PICs wiring setup (we connect PIC2 to PIC1's IRQ2);
- ICW4: extra systems information (we set PIC1 as Master and PIC2 as slave).

It then masks the Interrupt Mask Register, blocking all IRQs but #2 initially.
These must be unmasked on demand. The IMR is 8-bits long, so setting the n^th bit to 1
would DISABLE the IRQ n while setting it to 0 would ENABLE IRQ n.

As stated, this is an implementation of the legacy 8259 PIC. More
investigation is needed so we decide if it is enough or if we need
the (newer) APIC implementation instead.

This patch also adds the outb() helper function to helpers.h. The helpers
is a wrapper for assembly 'out' instruction.

Finally, since we now properly support hardware interrupts, this patch
also enables IRQs in platform main().

More information:
- Quark X1000 Datasheet, section 21.12, page 898.
- http://wiki.osdev.org/8259_PIC
- http://stanislavs.org/helppc/8259.html

cpu/x86/Makefile.x86

@@ -1,4 +1,4 @@
-CONTIKI_CPU_DIRS = .
+CONTIKI_CPU_DIRS = . drivers
 
 CONTIKI_SOURCEFILES += mtarch.c gdt.c helpers.S idt.c cpu.c
 

cpu/x86/cpu.c

@@ -29,9 +29,10 @@
  */
 
 #include "gdt.h"
+#include "helpers.h"
 #include "idt.h"
 #include "interrupt.h"
-#include "helpers.h"
+#include "pic.h"
 
 static void
 double_fault_handler(struct interrupt_context context)
@@ -49,4 +50,6 @@ cpu_init(void)
    * the system to triple fault, leaving no trace about what happened.
    */
   SET_INTERRUPT_HANDLER(8, 1, double_fault_handler);
+
+  pic_init();
 }

cpu/x86/drivers/pic.h

@@ -0,0 +1,70 @@
+/*
+ * 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 PIC_H
+#define PIC_H
+
+#include "helpers.h"
+
+#define PIC1_CMD_PORT   0x20
+#define PIC1_DATA_PORT  0x21
+#define PIC2_CMD_PORT   0xA0
+#define PIC2_DATA_PORT  0xA1
+
+/* 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.
+ */
+static inline void
+pic_init(void)
+{
+  /* ICW1: Initialization. */
+  outb(PIC1_CMD_PORT, 0x11);
+  outb(PIC2_CMD_PORT, 0x11);
+
+  /* ICW2: Remap IRQs by setting an IDT Offset for each PIC. */
+  outb(PIC1_DATA_PORT, 0x20);
+  outb(PIC2_DATA_PORT, 0x28);
+
+  /* ICW3: Setup Slave to Master's IRQ2. */
+  outb(PIC1_DATA_PORT, 0x04);
+  outb(PIC2_DATA_PORT, 0x02);
+
+  /* ICW4: Environment setup. Set PIC1 as master and PIC2 as slave. */
+  outb(PIC1_DATA_PORT, 0x01);
+  outb(PIC2_DATA_PORT, 0x01);
+
+  /* Set the IMR register, masking all hardware interrupts but IRQ 2.
+   * We will have to unmask each IRQ when registering them. */
+  outb(PIC1_DATA_PORT, 0xfb);
+  outb(PIC2_DATA_PORT, 0xff);
+}
+
+#endif /* PIC_H */

cpu/x86/helpers.S

@@ -35,3 +35,10 @@ halt:
         cli
 die:    hlt
         jmp die
+
+.global outb
+outb:
+        mov 4(%esp), %dx
+        mov 8(%esp), %al
+        out %al, %dx
+        ret

cpu/x86/helpers.h

@@ -31,8 +31,16 @@
 #ifndef HELPERS_H
 #define HELPERS_H
 
+#include <stdint.h>
+
 #define BIT(n) (1UL << (n))
 
 void halt(void) __attribute__((__noreturn__));
 
+/**
+ * Wrapper for the assembly 'out' instruction.
+ *
+ */
+void outb(uint16_t port, uint8_t byte);
+
 #endif /* HELPERS_H */

platform/galileo/contiki-main.c

@@ -30,12 +30,15 @@
 
 #include "contiki.h"
 #include "cpu.h"
+#include "interrupt.h"
 
 int
 main(void)
 {
   cpu_init();
 
+  ENABLE_IRQ();
+
   process_init();
   autostart_start(autostart_processes);