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x86: Disable NMI while initializing RTC

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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
This commit is contained in:
Andre Guedes 2015-05-06 15:24:43 -03:00 • committed by Jesus Sanchez-Palencia
parent a8849b2909
commit cb0510ebcf
4 changed files with 95 additions and 5 deletions
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13
cpu/x86/drivers/legacy_pc/rtc.c
View file

@ -30,6 +30,7 @@
#include "drivers/legacy_pc/rtc.h"
#include "drivers/legacy_pc/pic.h"
#include "drivers/legacy_pc/nmi.h"
#include "helpers.h"
#include "interrupt.h"
@ -72,19 +73,23 @@ rtc_init(rtc_frequency_t frequency, void (*callback)(void))
SET_INTERRUPT_HANDLER(RTC_INT, 0, rtc_handler);
nmi_disable();
/* Select interrupt period to 7.8125 ms */
outb(RTC_INDEX_REGISTER, 0x0A);
outb(RTC_INDEX_REGISTER, 0x8A);
reg_a = inb(RTC_TARGET_REGISTER);
reg_a &= 0xF0;
reg_a |= frequency;
outb(RTC_INDEX_REGISTER, 0x0A);
outb(RTC_INDEX_REGISTER, 0x8A);
outb(RTC_TARGET_REGISTER, reg_a);
/* Enable periodic interrupt */
outb(RTC_INDEX_REGISTER, 0x0B);
outb(RTC_INDEX_REGISTER, 0x8B);
reg_b = inb(RTC_TARGET_REGISTER);
outb(RTC_INDEX_REGISTER, 0x0B);
outb(RTC_INDEX_REGISTER, 0x8B);
outb(RTC_TARGET_REGISTER, reg_b | BIT(6));
nmi_enable();
pic_unmask_irq(RTC_IRQ);
}