os-faq-isr.html
来自「教导你怎么样写你自己的操作系统,并且列出来其它操作系统作为举例.」· HTML 代码 · 共 138 行
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<html><head> <title>Operating Systems FAQ :: ISR :: Interrupt Service Routines</title> <link rel=stylesheet type="text/css" href="default.css"></head><body><TABLE border="0" width="100%"> <TR> <TD><H2><A name="isr">ISR :: Interrupt Service Routines</A></H2> </TD> </TR> <TR> <TD>The x86 architecture is an interrupt driven system. External events are processed by interrupt service routines (ISR's) whose offsets are stored in the IDT (interrupt descriptor table). <p>These events can be hardware driven interrupts or software driven interrupts. </p> <p>An example of a hardware ISR is the keyboard. Every time you press a key, the keyboard signales to the IRQ1 which runs an interrupt. </p> <p>An example of a software driven interrupt is the services provided by MS-DOS, they use INT 21h and are signalled by software when to run. </p> </TD> </TR></TABLE><P> </P><TABLE border="0" width="100%"> <TR> <TD><H2><A name="normal_v_isr">Whats the difference between an ISR and normal routine?</A></H2> </TD> </TR> <TR> <TD>The difference between an ISR and a normal routine is very slight and has to do with CPU opcodes. <p>ISR routines end their routine with an "Interrupt Return (<b>IRET</b>)" whereas normal procedures end their routines with "Return (<b>RET</b>)" or "Far Return (<b>RETF</b>)" </p> <p>Some compilers do not have the ability to correctly create ISRs. Often a compiler introduces a non ansi compliant keyword "<b>_interrupt</b>" or "<b>interrupt</b>". Compilers known to support this keyword are Watcom C/C++, Borland C/C++, Microsoft C 6.0. However, GCC does not support this keyword for x86 architecture and it would seem Visual C/C++ does not. </p> <pre>/* example of clock tick routine in Watcom C/C++ */void <b>_interrupt</b> ISR_clock(void){ clock_count++;} </pre> </td> </tr></table><P> </P><TABLE border="0" width="100%"> <TR> <TD><H2><A name="gcc_isr">So how do I do an ISR in GCC?</A></H2> </TD> </TR> <TR> <TD>Doing an ISR in GCC is a little more complex than for compilers that support the "<b>_interrupt</b>" keyword. <p>You have to write a small routine in assembler to call your C routine. </p> <pre> /* Filename : isr_clock.s *//* GCC AT&T asm example for ISR routine *//* This example is for our clock_tick example *//* NOTE! This example assumes nothing in regards to contents of registers on running */ .globl _clock_isr .align 4 _clock_isr: /* save some registers */ pushl %eax pushl %ds pushl %es pushl %fs pushl %gs /* set our descriptors up to a DATA selector */ movl $0x10, %eax movw %ax, %ds movw %ax, %es movw %ax, %fs movw %ax, %gs /* call our clock routine */ call _ISR_clock /* clear the PIC (clock is a PIC interrupt) */ movl $0x20, %eax outb %al, $0x20 /* restor our regs */ popl %gs popl %fs popl %es popl %ds popl %eax iret /* filename : clock.c *//* clock routine *//* tell our linker clock_isr is not in this file */extern void clock_isr(void);__volatile__ unsigned long clock_count=0L;void ISR_clock(void){ clock_count++;} </pre> </td> </tr></table></body></html>⌨️ 快捷键说明
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