Brew interview questions and answers -P2

1.What difference is there between using the phone's "End" key to close an applet, and using the "Clear" key to close an applet?

An OEM of a particular device (phone) designates key(s) for the following two activities:
* A key, that when pressed, will close the current application. Most OEMs designate this to be the AVK_CLR key.
* A key, that when pressed, will close all applications. Most OEMs designate this to be the AVK_END key.
* When AVK_END is pressed, BREW will immediately send EVT_APP_STOP to the active applet without first sending the AVK_END key. In addition, the FreeAppData() callback routine provided to AEEApplet_New() will be called prior to unloading the applet; no other events or callbacks will occur.
* When AVK_CLR is pressed, BREW will first send this event to the applet. If the applet does not handle the event (i.e. returns FALSE in HandleEvent), only then BREW will close the application. In the implementation of your AVK_CLR handler, remember to also call FreeAppData as follows:
case AVK_CLR:
if (pMe->OnMainMenu == TRUE) {
// App is on main menu. Therefore pressing CLR key should cause app to exit
HelloWorld_FreeAppData(pi); //clean up
return FALSE; //return FALSE so that BREW will now close application
else { // Not on main menu.
// Therefore pressing CLR key should cause app to undo one level of menu
// nesting. Show previous menu in menu hierarchy
return TRUE;
Make sure that your FreeAppletData() properly cleans up all allocated memory and resources. All objects and interfaces created by CreateInstance, CreateDialog, MALLOC, etc., must have an associated call to Release or FREE.
2.How do I deal with a Low Battery Warning?
BREW sends the running application an EVT_APP_SUSPEND event in the case of a Low Battery Warning. In order to handle low battery condition, you must correctly handle EVT_APP_SUSPEND and EVT_APP_RESUME events.

3.What notification events can an app register for?
An app can register for the following System notifications:
TAPI (Class ID: 0x01001007)
TAPI Status change event
Incoming SMS
SMS message on specific Teleservice ID
Network layer is available
Network layer is closed
Network layer available and idle
Note: INETMGR NMASK_UDP_LISTEN has been deprecated and does not work.
An app can also register to receive notifications from other dynamic apps and modules.
4.How to test application for proper handling of Suspend/Resume events on a non- provisioned phone?
On the Kyocera 3035, you can test your app's handling of Suspend/Resume events by enabling automatic Keyguard (Main Menu->Settings->Keyguard) before running your app. When the Keyguard kicks in, the running app will receive a Suspend Event. The app will receive Resume event when the screen is unlocked.
On the Sharp Z-800, you can test your app's handling of Suspend/Resume events by setting the alarm to go off a few minutes in the future (Main Menu->Setup/Tools->Alarm->Daily Alarm) and then running the BREW app. Please note that in order for the app to be suspended when the alarm goes off, BREW Priority Setting must be off (Main Menu->Setup/Tools->BREW Priority Setting).
Memory Management :

5.How to recover the phone from an "UndefInst Exception?"
"Undef Inst Exception" stands for "undefined instruction exception," and means that the program pointer has jumped to a code segment that contains an undefined instruction. This can be the result of memory corruption, a stack overrun, or version-related incompatibilities between applet code and the BREW image on the phone.
Memory is tighter on the phone than when running on the emulator. Therefore, memory and stack overrun problems will be more likely to show up on the phone. You should double check memory related areas of your code, especially auto variable arrays and the maximum total size of allocated memory.
To clear the phone, pull the battery out for a few seconds.
6.What is a "Re-entrant Data Abort?"
The "Re-entrant Data Abort" exception is often caused by stack overrun. When an applet is running on the phone the stack size is small, and you are more likely to see stack overrun problems than when running on the emulator. Solutions to this problem are reducing the size or number of objects on the stack, and using objects allocated on the heap instead of automatic variables.
Note: Version-related incompatibilities between applet code and the BREW image on the phone can also lead to this type of exception.
7.What is a "Pref Abort Exception?"
A "Pref Abort Exception" usually indicates that memory important to the phone operating system has been trashed. The two most common causes of this exception are data corruption (i.e. running off the end of an array), and stack overruns.
8.What is an "SWI Exception?"
An "SWI Exception" is usually related to heap memory mismanagement. The most common causes of heap memory corruption are: overwriting the bounds of your allocated arrays, freeing objects more than once, and writing to wild or NULL pointers.
In addition to the more common causes, stack overrun can also lead to SWI Exceptions.
Note: It is recommended that large buffers be allocated on the heap rather than on the stack as automatic variables.
9.Why does the emulator display a blank screen with my application's name when my application exits?
Problem: When an application exits while running on the emulator, instead of returning to the main menu screen, a blank screen is displayed with the application name in the upper left corner.
This behavior is caused by not freeing all allocated memory before exiting the application. Any buffer you allocate using MALLOC or IHEAP_Malloc() must be freed using FREE or IHEAP_Free(). For any instance of a BREW class that you create, you must call the corresponding release function to free that instance.
10.How does the memory architecture in BREW work?
BREW device has Flash RAM and Heap RAM. You can treat Flash RAM as a hard drive. Programs are stored there, but not run from it. You can treat Heap RAM as you would always treat a memory heap. Say you have an application that is 35k in size. This will take 35k from the Flash RAM to store on the device. When the application is run, the 35k will be loaded into Heap RAM in its entirety plus however much Heap RAM it needs to allocate. When the applet is released, this Heap RAM is freed. It will still occupy space on the Flash RAM until it is removed from the device.
11.What is the size limit for an applet?
The size of a BREW applet is limited by the amount of free file system space that is available, and by the amount of available RAM.
BREW applets, when executed, are loaded into RAM; any RAM left over can be used for memory allocation, loading resources, creating controls, etc. How much RAM is available depends on the type of phone, and its configuration. On a QCP-3035, for instance, the available RAM is 90K, 30K of which belongs to BREW and other phone related tasks, leaving 60K available for use by an applet. The memory available on each of the phones running BREW is available here.
Another limiting factor for applet size is heap fragmentation. If the largest available memory block is smaller than the size of the applet, then the applet will not be loaded. Use IHEAP_CheckAvail() to determine whether a memory block of sufficient size can be allocated. IHEAP_GetMemStats() can be used to determine the amount of RAM already used. If you have an applet that is too large for a particular device, a work-around is to split the application into multiple applets. Memory Allocation provides more information on how to avoid heap fragmentation.
Note: In order test a low memory condition on the BREW Emulator reduce the heap size in the Device Configuration file by the appropriate amount. BREW's System Info screen reports the amount of available flash memory, not the amount of available RAM.
12.Why can't an applet be run directly from flash RAM?
BREW loads the apps into Heap RAM because files on EFS are stored as non- contiguous blocks.
13.What's the difference between MALLOC() and IHEAP_Malloc() function in BREW-SDK?
MALLOC and IHEAP_Malloc() are identical, just as FREE and IHEAP_Free() are identical. In earlier versions of the BREW SDK, malloc was part of the IHEAP Interface, and was later made into a helper function for ease of use. Both are still available for backward compatibility, but it is recommended that, use MALLOC and FREE rather than IHEAP_Malloc() and IHEAP_Free().
An app needs to create IHeap interface only when it wants to get current memory usage statistics (IHEAP_GetMemStats()) or check if a memory block of a certain size can be allocated (IHEAP_CheckAvail()).
14.What events must an applet handle?
In addition to the obvious EVT_APP_START and EVT_APP_STOP, your applet must support EVT_APP_SUSPEND and EVT_APP_RESUME in order to pass True BREW Testing.
15.How to test an application on the emulator to determine if it behaves properly under low memory conditions?
This can be achieved by reducing the heap size in the device configurator file (.qsc file) to almost the size of the .mod file. Any run time allocations by the applications should fail and you can test if your application deals with those failures correctly.
* Since the size of the mod file a is a lot less then the dll that runs in the emulator, the emulator approximates the size of the mod file to be 10% of dll.
* To properly run this test, create a separate directory that contains only the MIF of the application under test and have emulator point to this new directory (File->Change MIF Dir).

No comments:

Top Blogs