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S3C2440A RISC MICROPROCESSOR INTERRUPT CONTROLLER
14-7
INTERRUPT CONTROLLER SPECIAL REGISTERS
There are five control registers in the interrupt controller: source pending register, interrupt mode register, mask
register, priority register, and interrupt pending register.
All the interrupt requests from the interrupt sources are first registered in the source pending register. They are
divided into two groups including Fast Interrupt Request (FIQ) and Interrupt Request (IRQ), based on the interrupt
mode register. The arbitration procedure for multiple IRQs is based on the priority register.
SOURCE PENDING (SRCPND) REGISTER
The SRCPND register is composed of 32 bits each of which is related to an interrupt source. Each bit is set to 1 if
the corresponding interrupt source generates the interrupt request and waits for the interrupt to be serviced.
Accordingly, this register indicates which interrupt source is waiting for the request to be serviced. Note that each
bit of the SRCPND register is automatically set by the interrupt sources regardless of the masking bits in the
INTMASK register. In addition, the SRCPND register is not affected by the priority logic of interrupt controller.
In the interrupt service routine for a specific interrupt source, the corresponding bit of the SRCPND register has to
be cleared to get the interrupt request from the same source correctly. If you return from the ISR without clearing
the bit, the interrupt controller operates as if another interrupt request came in from the same source. In other
words, if a specific bit of the SRCPND register is set to 1, it is always considered as a valid interrupt request
waiting to be serviced.
The time to clear the corresponding bit depends on the user's requirement. If you want to receive another valid
request from the same source, you should clear the corresponding bit first, and then enable the interrupt.
You can clear a specific bit of the SRCPND register by writing a data to this register. It clears only the bit positions
of the SRCPND corresponding to those set to one in the data. The bit positions corresponding to those that are set
to 0 in the data remains as they are.
Register Address R/W Description Reset Value
SRCPND 0X4A000000 R/W Indicate the interrupt request status.
0 = The interrupt has not been requested.
1 = The interrupt source has asserted the interrupt
request.
0x00000000