PIC

Programmable Interrupt Controller. More...

Collaboration diagram for PIC:

Macros
#define	PIC1_CMD   0x20
	the master PIC's command port
#define	PIC1_DATA   0x21
	the master PIC's data port
#define	PIC2_CMD   0xA0
	the slave PIC's command port
#define	PIC2_DATA   0xA1
	the slave PIC's data port
#define	PIC_EOI   0x20
	"end of interrupt" signals that an IRQ has been handled
#define	INT_IRQ0   0x20
	where we want to map the master PIC's IRQs
#define	INT_IRQ8   0x28
	where we want to map the slave PIC's IRQs

Functions
void	pic_init ()
	Initializes the PIC. More...
void	pic_send_eoi (uint8_t intr)
	Sends an "end of interrupt" signal. More...

Detailed Description

Programmable Interrupt Controller.

The PIC manages IRQs (hardware interrupts). It maps actual IRQs to interrupt vectors. After booting, the IRQs need to be remapped to avoid conflicts.

See also

http://wiki.osdev.org/8259_PIC

http://www.lowlevel.eu/wiki/PIC

Function Documentation

void pic_init

(

)

Initializes the PIC.

Before PIC initialization the interrupt vectors look like this:

• 00-1F: Exceptions
• 08-0F: IRQ0-7 (PIC1) - conflicts with exceptions!
• 70-77: IRQ8-15 (PIC2)

We "bend" the mapping "IRQ -> interrupt vector" to prevent those conflicts by re-initializing the master and slave PICs and setting the interrupt vectors 0x20 and 0x28 respectively.

So after initialization we have this:

• 00-1F: Exceptions
• 20-27: IRQ0-7 (PIC1) - no more conflicts, all IRQs 0-15 are in a row
• 28-2F: IRQ8-15 (PIC2)
• 30-FF: freely usable (syscalls)

Definition at line 25 of file pic.c.

void pic_send_eoi

(

uint8_t

intr

)

Sends an "end of interrupt" signal.

This tells the master PIC that we're ready to process new interrupts. No new interrupts are fired until an EOI is sent.

Parameters

intr	the interrupt vector that has been handled

For IRQ8-15 (issued by slave), we send an EOI to the slave PIC as well.

Definition at line 61 of file pic.c.

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