osd-contiki/cpu/x86/drivers/legacy_pc/nmi.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

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1.9 KiB
C

/*
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#include "helpers.h"
#define NMI_ENABLE_PORT 0x70
void
nmi_enable(void)
{
uint8_t value = inb(NMI_ENABLE_PORT);
outb(NMI_ENABLE_PORT, value & ~BIT(8));
}
/*---------------------------------------------------------------------------*/
void
nmi_disable(void)
{
uint8_t value = inb(NMI_ENABLE_PORT);
outb(NMI_ENABLE_PORT, value | BIT(8));
}