WinCE

Here is another really informative article by the Windows CE Base team.:)

http://blogs.msdn.com/ce_base/archive/2007/11/26/How-does-Windows-Embedded-CE-6.0-start_3F00_.aspx

In my previous post, I have explained how to add an interrupt when source code is available.

Now I will explain how to handle an interrupt by writing an IST in the driver. For the reason of continuity, I am using the same power button driver and the Wireless Activity Interrupt (as I explain with in post "Adding Interrupt in OAL").

1. Create an even to be associated with the interrupt

HANDLE g_WlanActiveEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
if( !g_WlanActiveEvent)
{
RETAILMSG(1, (TEXT("WlanActivityMonitorStart: Failed to create Intterupt Event\r\n")));
goto CleanUp;
}

2. Associate the Interrupt with the event using SYSINTR value

UINT32 g_SysIntr = SYSINTR_WLAN;
......
result = InterruptInitialize(g_SysIntr, g_WlanActiveEvent, NULL, 0);
if(!result)
{
RETAILMSG(1, (TEXT("WlanActivityMonitorStart: InterruptInitialize() failed. GetLastError=0x%x\r
\n"),GetLastError()));
goto CleanUp;
}

3. Start a thread for handling the interrupt.

g_WlanThread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE) WlanThread, NULL, 0, NULL);
if ( g_WlanThread == NULL )
{
RETAILMSG(1, (TEXT("WlanActivityMonitorStart: Failed to create WlanActive
Intterupt Thread\r\n")));
goto CleanUp;
}

4. In the thread, wait for the event to happen using the WaitForSingleObject or WaitForMultipleObjects API.

INT WlanThread (VOID)
{
while(!g_FlagExitThrd)
{
WaitForSingleObject(g_WlanActiveEvent, INFINITE);
.............
}
return ERROR_SUCCESS;
}

5. Perform the necessary operations to service that interrupt. Here I am pulsing another event to notify some other sets of appication.

WaitForSingleObject(g_WlanActiveEvent, INFINITE);
InterruptMask(g_SysIntr,TRUE);

if (g_WlanEvent)
{
RETAILMSG(1, (TEXT("WlanThread: Intterupt \r\n")));
PulseEvent(g_WlanEvent);
}

Sleep (1000); // Sleep to ignore some activity as this line toggles a lot
InterruptMask(g_SysIntr,FALSE);

6. Signal the completion of interrupt handling using InterruptDone

InterruptDone(g_SysIntr);

When we are having the whole BSP source, there will be cases in which we may need to add interrupt in OAL. This can be accommodate a new driver or add a new functionality to the existing one.

For explaining the procedure I am using the Mainstone BSP that is available in windows ce. Lets assume that we want to add an interrupt for Wireless LAN activity. This interrupt line will be a GPIO line which is mapped to GPIO 91 of PXA.

These are the files that need modification:
* bsp_cfg.h (Src\Inc)
* intr.c (OAL)

In 'bsp_cfg.h', you need to define a SYSINTR (if needed) for the new interrupt that you are about to add.

.............
#define SYSINTR_PWRBTN (SYSINTR_FIRMWARE+14) // 30
#define SYSINTR_WLANACTIVE (SYSINTR_FIRMWARE+15) // 31 - The new interrupt
................

Now in OAL, intr.c, make the following changes:
1. In BSPIntrInit() function, add a call to OALIntrStaticTranslate() to map the
the new SYSINTR v alue to the GPIO.

...............
OALIntrStaticTranslate (SYSINTR_WLAN,IRQ_GPIOXX_2_GPIO91);
...............

2. In BSPIntrEnableIrq(), add the case of enabling the GPIO Interrupt

.................
else if (irq == IRQ_GPIOXX_2_GPIO91)
{
EnableGPIO91Irq(); // define this function for enabling falling or rising
//edge detect and clear edge detect
}
.................

3. In BSPIntrDisableIrq(), add the case of enabling the GPIO Interrupt

.................
else if (irq == IRQ_GPIOXX_2_GPIO91)
{
DisableGPIO91Irq(); // define this function for clearing falling rising
//edge detect so that interrupt wont come
}
.................

4. Define the functions for enabling and disabling the gpio interrupt

............
//~~ Function for disabling gpio91 interrupt
static void EnableGPIO91Irq(void)
{
SETREG32((PULONG)&g_pGPIORegs->GRER2, XLLP_BIT_27);
}

//~~ Function for enabling gpio91 interrupt
static void DisableGPIO91Irq(void)
{
CLRREG32((PULONG)&g_pGPIORegs->GEDR2, XLLP_BIT_27);
CLRREG32((PULONG)&g_pGPIORegs->GRER2, XLLP_BIT_27);
}

This is how we add a new interrupt in OAL.

My friend mukesh has written in his blog, how to dynamically add an interrupt handler, when OAL source code is not available.

In the next posts, I will explain how to add an IST (Interrupt Service Thread) to take care of this interrupt.