I Can't Get Interrupts Working: Difference between revisions
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m Fixed some grammar mistakes. |
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Use the mask feature of the PIC to enable/disable some handlers. |
Use the mask feature of the PIC to enable/disable some handlers. |
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<source lang="c"> |
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<pre> |
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outb(0x21,0xfd); |
outb(0x21,0xfd); |
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outb(0xa1,0xff); |
outb(0xa1,0xff); |
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enable(); // asm("sti"); |
enable(); // asm("sti"); |
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</ |
</source> |
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=== I'm receiving EXC9 instead of IRQ1 when striking a key ?! === |
=== I'm receiving EXC9 instead of IRQ1 when striking a key ?! === |
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=== I can only receive one IRQ === |
=== I can only receive one IRQ === |
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Each IRQ needs to be acknowledged to the PIC manually. You need to have < |
Each IRQ needs to be acknowledged to the PIC manually. You need to have <source lang="c"> outb(0x20,0x20) </source> within any master handler and any <source lang="c"> outb(0x20,0x20); outb(0xa0,0x20); </source> within any slave handler. |
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=== When I try to enable the PIT, the keyboard doesn't work anymore === |
=== When I try to enable the PIT, the keyboard doesn't work anymore === |
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=== I keep getting an IRQ7 for no apparent reason === |
=== I keep getting an IRQ7 for no apparent reason === |
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This is a known problem that cannot be prevented from happening, although there is a workaround. When any IRQ7 is received, simply read the In-Service Register < |
This is a known problem that cannot be prevented from happening, although there is a workaround. When any IRQ7 is received, simply read the In-Service Register <source lang="c"> outb(0x20, 0x0B); unsigned char irr = inb(0x20);</source> and check if bit 7 <source lang="c">irr & 0x80</source> is set. If it isn't, then return from the interrupt without sending an EOI. |
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For more information, including a more detailed explanation, see Brendan's post in [[Topic:11379|this thread]]. |
For more information, including a more detailed explanation, see Brendan's post in [[Topic:11379|this thread]]. |
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You're trying to load a 16-bits field (a part of the IDT descriptor) with a reference to a 32-bit label that is subject to relocation. Try to replace |
You're trying to load a 16-bits field (a part of the IDT descriptor) with a reference to a 32-bit label that is subject to relocation. Try to replace |
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<source lang="asm"> |
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isr_label: |
isr_label: |
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iret |
iret |
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dw 0xbeef |
dw 0xbeef |
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dw isr_label >> 16 |
dw isr_label >> 16 |
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</source> |
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by something that extracts a 'pure value' from the address (e.g. the difference of two addresses are a pure value and <tt>$$</tt> means to NASM the start of the section) |
by something that extracts a 'pure value' from the address (e.g. the difference of two addresses are a pure value and <tt>$$</tt> means to NASM the start of the section) |
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<source lang="asm"> |
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%define BASE_OF_SECTION SOME_CONSTANT_YOU_SHOULD_KNOW |
%define BASE_OF_SECTION SOME_CONSTANT_YOU_SHOULD_KNOW |
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isr_label: |
isr_label: |
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dw 0xbabe |
dw 0xbabe |
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dw (BASE_OF_SECTION isr_label - $$) >> 16 |
dw (BASE_OF_SECTION isr_label - $$) >> 16 |
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</source> |
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The role of <pre>BASE_OF_SECTION</pre> is to adjust the pure offset to the real situation (usually as defined in your linker script), e.g. if your kernel get loaded at 1MB, you'll set it to 0x100000 to keep the CPU happy. |
The role of <pre>BASE_OF_SECTION</pre> is to adjust the pure offset to the real situation (usually as defined in your linker script), e.g. if your kernel get loaded at 1MB, you'll set it to 0x100000 to keep the CPU happy. |
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==Assembly Example== |
==Assembly Example== |
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<source lang="asm"> |
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int_handler: |
int_handler: |
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mov ax, LINEAR_DATA_SELECTOR |
mov ax, LINEAR_DATA_SELECTOR |
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mov [idt+49*8+6],ax |
mov [idt+49*8+6],ax |
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int 49 |
int 49 |
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</source> |
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should display a smiley on the top-left corner ... then the CPU is halted indefinitely. |
should display a smiley on the top-left corner ... then the CPU is halted indefinitely. |
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simple, but not like Nasm. |
simple, but not like Nasm. |
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a little example, so you can see how it works: |
a little example, so you can see how it works: |
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<source lang="asm"> |
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idt: |
idt: |
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dw ((isr1 shl 0x30) shr 0x30) ; the low part of the address |
dw ((isr1 shl 0x30) shr 0x30) ; the low part of the address |
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db 010001110b ; type |
db 010001110b ; type |
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dw (isr1 shr 0x10) the high part of the address |
dw (isr1 shr 0x10) the high part of the address |
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isr1: |
isr1: |
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mov ax,0xdead |
mov ax,0xdead |
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</source> |
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