contiki/cpu/x86/drivers/legacy_pc/rtc.c
Andre Guedes cb0510ebcf x86: Disable NMI while initializing RTC
According to [1], we should disable non-maskable and maskable interrupts
while initializing RTC. Otherwise, the RTC may be left in an undefined
state (non-functional) if an interrupt occurs. Currently, maskable
interrupts are already disabled, but NMI is not.

This patch adds helpers APIs to enable/disable non-maskable interrupts
(NMI) and changes rtc_init() to disable NMI while initializing the RTC.

NMI enable/disable code is legacy-PC specific therefore it was put in
driver/legacy_pc/ directory.

Regarding the RTC initialization changes, just calling nmi_disable() and
nmi_enable is not enough since NMI and RTC share the same IO port. So We
should also set the NMI_ENABLE bit while selecting the RTC_INDEX.

Additionally, the nmi_disable() call is not strictly required since we
set the NMI_ENABLE bit while selecting the RTC_INDEX. However, to make
clear hat we are disabling NMI and to improve readability (by matching
NMI disable/enable), the nmi_disable() call was purposely used.

[1] http://wiki.osdev.org/RTC
2015-12-21 08:06:14 -02:00

96 lines
3.3 KiB
C

/*
* Copyright (C) 2015, Intel Corporation. All rights reserved.
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*/
#include "drivers/legacy_pc/rtc.h"
#include "drivers/legacy_pc/pic.h"
#include "drivers/legacy_pc/nmi.h"
#include "helpers.h"
#include "interrupt.h"
#define RTC_INDEX_REGISTER 0x70
#define RTC_TARGET_REGISTER 0x71
#define RTC_IRQ 8
#define RTC_INT PIC_INT(RTC_IRQ)
static void (*user_callback)(void);
static void
rtc_handler()
{
user_callback();
/* Clear Register C otherwise interrupts will not happen again.
* Register C is automatically cleared when it is read so we do
* a dummy read to clear it.
*/
outb(RTC_INDEX_REGISTER, 0x0C);
inb(RTC_TARGET_REGISTER);
/* Issue the End of Interrupt to PIC */
pic_eoi(RTC_IRQ);
}
/*---------------------------------------------------------------------------*/
/* Initialize the Real Time Clock.
* @frequency: RTC has very specific values for frequency. They are: 2, 4, 8,
* 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, and 8192 Hz.
* value otherwise it will not work properly.
* @callback: This callback is called every time the RTC IRQ is raised.
* It is executed in interrupt context.
*/
void
rtc_init(rtc_frequency_t frequency, void (*callback)(void))
{
uint8_t reg_a, reg_b;
user_callback = callback;
SET_INTERRUPT_HANDLER(RTC_INT, 0, rtc_handler);
nmi_disable();
/* Select interrupt period to 7.8125 ms */
outb(RTC_INDEX_REGISTER, 0x8A);
reg_a = inb(RTC_TARGET_REGISTER);
reg_a &= 0xF0;
reg_a |= frequency;
outb(RTC_INDEX_REGISTER, 0x8A);
outb(RTC_TARGET_REGISTER, reg_a);
/* Enable periodic interrupt */
outb(RTC_INDEX_REGISTER, 0x8B);
reg_b = inb(RTC_TARGET_REGISTER);
outb(RTC_INDEX_REGISTER, 0x8B);
outb(RTC_TARGET_REGISTER, reg_b | BIT(6));
nmi_enable();
pic_unmask_irq(RTC_IRQ);
}