S3c2440支持多达36个内部中断源和24个外部中断源，分别使用内部终端屏蔽寄存器INTMSK和外部中断寄存器MSK进行屏蔽控制。其中，外部中断源通过GPIO以复用的方式成为内部中断源的一部分。
但是我们清楚，INTMSK是一个32位的寄存器，最多只能支持32中断，它是如何对应这么多中断的呢？
首先我们先看INTMSK对应的位。
INTERRUPT MASK (INTMSK) REGISTER (Continued)
INT_ADC [31] 0 = Service available, 1 = Masked 1
INT_RTC [30] 0 = Service available, 1 = Masked 1
INT_SPI1 [29] 0 = Service available, 1 = Masked 1
INT_UART0 [28] 0 = Service available, 1 = Masked 1
INT_IIC [27] 0 = Service available, 1 = Masked 1
INT_USBH [26] 0 = Service available, 1 = Masked 1
INT_USBD [25] 0 = Service available, 1 = Masked 1
INT_NFCON [24] 0 = Service available, 1 = Masked 1
INT_UART1 [23] 0 = Service available, 1 = Masked 1
INT_SPI0 [22] 0 = Service available, 1 = Masked 1
INT_SDI [21] 0 = Service available, 1 = Masked 1
INT_DMA3 [20] 0 = Service available, 1 = Masked 1
INT_DMA2 [19] 0 = Service available, 1 = Masked 1
INT_DMA1 [18] 0 = Service available, 1 = Masked 1
INT_DMA0 [17] 0 = Service available, 1 = Masked 1
INT_LCD [16] 0 = Service available, 1 = Masked 1
INT_UART2 [15] 0 = Service available, 1 = Masked 1
INT_TIMER4 [14] 0 = Service available, 1 = Masked 1
INT_TIMER3 [13] 0 = Service available, 1 = Masked 1
INT_TIMER2 [12] 0 = Service available, 1 = Masked 1
INT_TIMER1 [11] 0 = Service available, 1 = Masked 1
INT_TIMER0 [10] 0 = Service available, 1 = Masked 1
INT_WDT_AC97 [9] 0 = Service available, 1 = Masked 1
INT_TICK [8] 0 = Service available, 1 = Masked 1
nBATT_FLT [7] 0 = Service available, 1 = Masked 1
INT_CAM [6] 0 = Service available, 1 = Masked 1
EINT8_23 [5] 0 = Service available, 1 = Masked 1
EINT4_7 [4] 0 = Service available, 1 = Masked 1
EINT3 [3] 0 = Service available, 1 = Masked 1
EINT2 [2] 0 = Service available, 1 = Masked 1
EINT1 [1] 0 = Service available, 1 = Masked 1
EINT0 [0] 0 = Service available, 1 = Masked 1
我们发现INTMSK的第5，6位对应了EINT4_7, EINT8_23，20个外部中断，也就是所，这20个GPIO引脚只能触发这两个中断。
但是当中断到来时，我们如果判断是由哪一个GPIO引脚触发的呢？这个时候我们可以通过查询EINTMASK来判断中断源。
EINTMASK Bit Description
EINT23 [23] 0 = enable interrupt 1= masked
EINT22 [22] 0 = enable interrupt 1= masked
EINT21 [21] 0 = enable interrupt 1= masked
EINT20 [20] 0 = enable interrupt 1= masked
EINT19 [19] 0 = enable interrupt 1= masked
EINT18 [18] 0 = enable interrupt 1= masked
EINT17 [17] 0 = enable interrupt 1= masked
EINT16 [16] 0 = enable interrupt 1= masked
EINT15 [15] 0 = enable interrupt 1= masked
EINT14 [14] 0 = enable interrupt 1= masked
EINT13 [13] 0 = enable interrupt 1= masked
EINT12 [12] 0 = enable interrupt 1= masked
EINT11 [11] 0 = enable interrupt 1= masked
EINT10 [10] 0 = enable interrupt 1= masked
EINT9 [9] 0 = enable interrupt 1= masked
EINT8 [8] 0 = enable interrupt 1= masked
EINT7 [7] 0 = enable interrupt 1= masked
EINT6 [6] 0 = enable interrupt 1= masked
EINT5 [5] 0 = enable interrupt 1= masked
EINT4 [4] 0 = enable interrupt 1= masked
Reserved [3:0] Reserved
但是还有一个疑问，不是说60个中断源吗？除去24个外部中断源应该还有60-24 -(32-6)=10个内部中断源啊。他们在哪呢？
其实这里涉及到了子中断源的概念。
Sub Sources Descriptions Source
INT_AC97 AC97 interrupt INT_WDT_AC97
INT_WDT Watchdoc interrupt INT_WDT_AC97
INT_CAM_P P-port capture interrupt in camera interface INT_CAM
INT_CAM_C C-port capture interrupt in camera interface INT_CAM
INT_ADC_S ADC interrupt INT_ADC
INT_TC Touch screen interrupt (pen up/down) INT_ADC
INT_ERR2 UART2 error interrupt INT_UART2
INT_TXD2 UART2 transmit interrupt INT_UART2
INT_RXD2 UART2 receive interrupt INT_UART2
INT_ERR1 UART1 error interrupt INT_UART1
INT_TXD1 UART1 transmit interrupt I NT_UART1
INT_RXD1 UART1 receive interrupt INT_UART1
INT_ERR0 UART0 error interrupt INT_UART0
INT_TXD0 UART0 transmit interrupt INT_UART0
INT_RXD0 UART0 receive interrupt NT_UART0