This page explains the exception display system used by NitroSDK to show information about exceptions generated on ARM processors.
NitroSDK includes a system for displaying information when processor exceptions occur. The register and type of exception get displayed. The exception display system is enabled by initialization using OS_InitException()OS_Init()OS_Init()
This initialization function sets the SDK exception vector (the address for transfer of control when an exception occurs) to the address of the function that displays exceptions. IS-NITRO-DEBUGGER does not perform this exception display process because some debug features make use of exceptions. The current operating environment is determined automatically, so nothing is required from the application.
The exception display system is a debug feature, so it is disabled in the FINALROM build.
The ARM processor specifications allow you to set the exception vectors at either addresses 0x00000000 to 0x0000001C or 0xFFFF0000 to 0xFFFF001C. The former are called normal vectors, while the latter are called high vectors.
OS_SetExceptionVectorLower()0x0000000 to 0x0000001C (normal vectors).
OS_SetExceptionVectorUpper()0xFFFF0000 to 0xFFFF001C (high vectors).
NitroSDK uses the high vectors by default. Unless you have a special reason, use the high vectors and do not change the settings.
When exceptions occur, control can be transferred to a user-specified exception handler. To do this, register the handler with OS_SetUserExceptionHandler()
The following exceptions exist for ARM:
| Exception type | Normal vector address | High vector address |
|---|---|---|
| Reset | 0x00000000 |
0xFFFF0000 |
| Undefined instructions | 0x00000004 |
0xFFFF0004 |
| Software interrupt | 0x00000008 |
0xFFFF0008 |
| Pre-fetch abort | 0x0000000C |
0xFFFF000C |
| Data abort | 0x00000010 |
0xFFFF0010 |
| IRQ | 0x00000018 |
0xFFFF0018 |
| FIQ | 0x0000001C |
0xFFFF001C |
Because IRQ exceptions are used as interrupts, they are excluded from the process flow described below. (For more details, see
When an exception occurs, control is transferred to the pertinent vector address, as shown in the table above. This normally involves use of high vector addresses.
After that, if IS-NITRO-DEBUGGER is being used, control is transferred to a special debugger process routine. The program is reset for this debugger process, so the flow steps described below are for cases where IS-NITRO-DEBUGGER is not being used.
If IS-NITRO-DEBUGGER is not being used, control is transferred to the address stored in DTCM's HW_EXCP_VECTOR_BUF0x3FDC. In the ARM7, this address takes position at the dedicated work RAM offset 0x7FDC. Here, what gets set is the address of the NitroSDK function for displaying exception information. (This is set by OS_InitException()
The user handler is called within this routine (if a user handler was registered with OS_SetUserExceptionHandler()
In the example below, a data abort exception has occurred. The high vector fake address for a data abort exception is 0xFFFF0010, so the process jumps to 0xFFFF0010. This leads to the address stored in HW_EXCP_VECTOR_BUF

List of OS Functions (Exception)
11/16/2004 Initial version