中断及设备初始化

硬件中断

1. 主板上的设备会产生中断, 常见的中断有
   • 用户键盘输入
   • 读写磁盘存储
   • 时钟中断
2. xv6 需要设置中断处理程序，来保证操作系统可以正常运行
   • 中断处理流程和系统调用过程类似
   • 大体流程是：主板硬件产生一个信号，我们对设备编程产生中断，然后 CPU 接受中断
3. 可以理解中断是来自硬件的

PIC 中断

1. PIC 早期单核中断处理单元
   • 处理程序位于 picirq.c
   • 早期单个 PIC 最多支持 8 个中断，受限与设备引脚数量
     • 主 PIC: IRQ0 ~ IRQ7
     • 从 PIC: IRQ8 ~ IRQ16
   • inb/outb 指令配置主 PIC 产出 IRQ0 ~ IRQ7
   • xv6 直接关闭 PIC
2. 多核处理中断分为两个部分
   • lapic
   • ioapic
3. Local APIC
   • 本地 APIC, 位于单个 CPU 核心
   • lapicinit
   • 内存映射方式操作，而不是 inb/outb
4. IO APIC
   • I/O 系统中断
   • 内存映射方式操作，而不是 inb/outb
   • ioapicinit

(qemu) info lapic
dumping local APIC state for CPU 0

LVT0     0x00010000 active-hi edge  masked                      Fixed  (vec 0)
LVT1     0x00010000 active-hi edge  masked                      Fixed  (vec 0)
LVTPC    0x00010000 active-hi edge  masked                      Fixed  (vec 0)
LVTERR   0x00000033 active-hi edge                              Fixed  (vec 51)
LVTTHMR  0x00010000 active-hi edge  masked                      Fixed  (vec 0)
LVTT     0x00020020 active-hi edge                 periodic     Fixed  (vec 32)
Timer    DCR=0xb (divide by 1) initial_count = 10000000 current_count = 7172266
SPIV     0x0000013f APIC enabled, focus=off, spurious vec 63
ICR      0x00088500 physical level de-assert all-self
ICR2     0x00000000
ESR      0x00000000
ISR      (none)
IRR      32

APR 0x00 TPR 0x00 DFR 0x0f LDR 0x00 PPR 0x00
(qemu) info pic
pic1: irr=40 imr=ff isr=00 hprio=0 irq_base=70 rr_sel=0 elcr=0c fnm=0
pic0: irr=15 imr=ff isr=00 hprio=0 irq_base=08 rr_sel=0 elcr=00 fnm=0
ioapic0: ver=0x20 id=0x00 sel=0x00
  pin 0  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 1  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 2  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 3  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 4  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 5  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 6  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 7  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 8  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 9  0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 10 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 11 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 12 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 13 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 14 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 15 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 16 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 17 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 18 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 19 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 20 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 21 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 22 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  pin 23 0x0000000000010000 dest=0 vec=0   active-hi edge  masked fixed  physical
  IRR      (none)
  Remote IRR (none)
(qemu)

中断初始化

1. Local APIC 初始化 lapicinit
2. 时钟中断 file:../../study/os/xv6-public/lapic.c::lapicw(TICR, 10000000);
3. PIC 关闭 ../../study/os/xv6-public/picirq.c
4. IO APIC 初始化 ioapicinit
5. console 初始化 consoleinit
6. 键盘中断 file:../../study/os/xv6-public/console.c::ioapicenable(IRQ_KBD, 0);
7. UART 串口通信协议 uartinit
   • COM1 设置: baud, data bits, stop bit, parity
   • 开启 COM1
8. IDE 磁盘中断 －ideinit enable IRQ_IDE
   • SCSI/SATA