2015-09-29 23:55:54 +02:00
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/*
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2015-09-30 19:03:23 +02:00
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# PIT
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TODO get working
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2015-10-04 19:59:15 +02:00
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TODO answer with example:
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- http://stackoverflow.com/questions/13950264/does-using-tsc-as-clock-source-improve-timer-and-scheduling-granularity
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- http://stackoverflow.com/questions/26853905/use-of-irq0-pit-in-x86-linux
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- http://stackoverflow.com/questions/12229644/time-sources-in-x86-processors
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- http://stackoverflow.com/questions/26321531/pit-not-sending-interrupts-to-irq0
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TODO where is it documented?
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2015-09-30 19:03:23 +02:00
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Programmable interrupt timer.
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2015-10-04 19:59:15 +02:00
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Read this *now*: http://wiki.osdev.org/PIT
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2015-09-30 19:03:23 +02:00
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Can generate periodic interrupts, or sounds.
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2015-10-04 19:59:15 +02:00
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Has 3 channels that can generate 3 independent signals
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- channel 0 at port 0x40: generates interrupts
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- channel 1 at port 0x41: not to be used for some reason
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- channel 2 at port 0x42: linked to the speaker to generate sounds
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Port 0x43 is used to control signal properties except frequency
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(which goes in the channel ports) for the 3 channels.
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See osdev article for details.
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## PIC
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Programmable interrupt controller:
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2015-09-29 23:55:54 +02:00
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2015-10-04 19:59:15 +02:00
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- http://wiki.osdev.org/PIC
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- http://www.jamesmolloy.co.uk/tutorial_html/5.-IRQs%20and%20the%20PIT.html
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Controls interrupts. Ports:
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- 0x0020: Master PIC command
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- 0x0021: Master PIC data
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- 0x00A0: Slave PIC command
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- 0x00A1: Slave PIC Data
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### EOI
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End of interrupt.
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We must tell the PIC that we are at the end. TODO otherwise what?
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https://en.wikipedia.org/wiki/End_of_interrupt
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2015-09-30 19:03:23 +02:00
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## 1193181
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Magic number that is the frequency of the oscillator.
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http://f.osdev.org/viewtopic.php?f=1&t=15503
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2015-10-04 19:59:15 +02:00
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Frequency divisor.
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Produce 1000Hz signal.
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1193181 is the source frequency.
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This is an electronics concept:
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https://en.wikipedia.org/wiki/Frequency_divider
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2 occurrences on Linux 4.2.
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2015-09-30 19:03:23 +02:00
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## Bibliography
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- https://en.wikipedia.org/wiki/Intel_8253
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- http://kernelx.weebly.com/programmable-interval-timer.html
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2015-09-29 23:55:54 +02:00
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*/
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#include "common.h"
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2015-09-30 19:03:23 +02:00
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2015-09-29 23:55:54 +02:00
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BEGIN
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2015-10-04 19:59:15 +02:00
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/* Setup interrupt handler 0. */
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movw $handler, 0x00
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mov %cs, 0x02
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/*
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Define the properties of the wave:
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- Channel: 0
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- access mode: lobyte/hibyte
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- operating mode: rate generator
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- BCD/binary: binary
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*/
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mov $0b00110100, %al
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out %al, $0x43
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/*
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Set frequency of Channel 0.
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We have to split the 2 ax bytes,
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as we can only communicate one byte at a time here.
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*/
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.equ div, 1193181 / 1000
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mov div, %ax
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out %al, $0x40
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mov %ah, %al
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out %al, $0x40
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PUTC($0x61)
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sti
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loop:
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nop
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jmp loop
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handler:
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PUTC($0x61)
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iret
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/* TODO turn off. */
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