Samsung S3C84E5 user manual ENABLE/DISABLE Interrupt Instructions EI, DI

S3C84E5/C84E9/P84E9 INTERRUPT STRUCTURE

ENABLE/DISABLE INTERRUPT INSTRUCTIONS (EI, DI)

Executing the Enable Interrupts (EI) instruction globally enables the interrupt structure. All interrupts are then serviced as they occur according to the established priorities.

NOTE

The system initialization routine executed after a reset must always contain an EI instruction to globally enable the interrupt structure.

During the normal operation, you can execute the DI (Disable Interrupt) instruction at any time to globally disable interrupt processing. The EI and DI instructions change the value of bit 0 in the SYM register.

SYSTEM-LEVEL INTERRUPT CONTROL REGISTERS

In addition to the control registers for specific interrupt sources, four system-level registers control interrupt processing:

—The interrupt mask register, IMR, enables (un-masks) or disables (masks) interrupt levels.

—The interrupt priority register, IPR, controls the relative priorities of interrupt levels.

—The interrupt request register, IRQ, contains interrupt pending flags for each interrupt level (as opposed to each interrupt source).

—The system mode register, SYM, enables or disables global interrupt processing (SYM settings also enable fast interrupts and control the activity of external interface, if implemented).

Table 5-2. Interrupt Control Register Overview

Control Register	ID	R/W	Function Description
Interrupt mask register	IMR	R/W	Bit settings in the IMR register enable or disable interrupt
			processing for each of the eight interrupt levels: IRQ0–IRQ7.
Interrupt priority register	IPR	R/W	Controls the relative processing priorities of the interrupt levels.
			The seven levels of S3C84E5/C84E9/P84E9 are organized into
			three groups: A, B, and C. Group A is IRQ0 and IRQ1, group B
			is IRQ2, IRQ3 and IRQ4, and group C is IRQ5, IRQ6, and IRQ7.
Interrupt request register	IRQ	R	This register contains a request pending bit for each interrupt
			level.
System mode register	SYM	R/W	This register enables/disables fast interrupt processing, dynamic
			global interrupt processing.

NOTE: Before IMR register is changed to any value, all interrupts must be disable.

Using DI instruction is recommended.

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