ColdFire Core
MCF5253 Reference Manual, Rev. 1
Freescale Semiconductor
3-11
Because ColdFire processors do not support hardware stacking of multiple exceptions, it is the
responsibility of the operating system to check for trace mode after processing other exception types. For
example, consider the execution of a TRAP instruction while in trace mode. The processor will initiate the
TRAP exception and then pass control to the corresponding handler. If the system requires that a trace
exception be processed, it is the responsibility of the TRAP exception handler to check for this condition
(SR[15] in the exception stack frame asserted) and pass control to the trace handler before returning from
the original exception.
3.5.7
Debug Interrupt
This special type of program interrupt is covered in detail in
Chapter 20, “Background Debug Mode
This exception is generated in response to a hardware breakpoint register trigger. The
processor does not generate an IACK cycle but rather calculates the vector number internally (vector
number 12).
3.5.8
RTE and Format Error Exceptions
When an RTE instruction is executed, the processor first examines the 4-bit format field to validate the
frame type. For a ColdFire 5200 processor, any attempted execution of an RTE where the format is not
equal to {4,5,6,7} generates a format error. The exception stack frame for the format error is created
without disturbing the original RTE frame and the stacked PC pointing to the RTE instruction.
The selection of the format value provides some limited debug support for porting code from 68000
applications. On 680x0 family processors, the SR was located at the top of the stack. On those processors,
bit[30] of the longword addressed by the system stack pointer is typically zero. Thus, if an RTE is
attempted using this “old” format, it generates a format error on a ColdFire 5200 processor.
If the format field defines a valid type, the processor: (1) reloads the SR operand, (2) fetches the second
longword operand, (3) adjusts the stack pointer by adding the format value to the auto-incremented address
after the fetch of the first longword, and then (4) transfers control to the instruction address defined by the
second longword operand within the stack frame.
3.5.9
TRAP Instruction Exceptions
Executing TRAP always forces an exception and is useful for implementing system calls. The trap
instruction may be used to change from user to supervisor mode.
3.5.10
Interrupt Exception
The interrupt exception processing, with interrupt recognition and vector fetching, includes uninitialized
and spurious interrupts as well as those where the requesting device supplies the 8-bit interrupt vector.
Autovectoring may optionally be supported through the System Integration module (SIM).
Summary of Contents for MCF5253
Page 1: ...Document Number MCF5253RM Rev 1 08 2008 MCF5253 Reference Manual...
Page 26: ...MCF5253 Reference Manual Rev 1 xxvi Freescale Semiconductor...
Page 32: ...MCF5253 Reference Manual Rev 1 xxxii Freescale Semiconductor...
Page 46: ...MCF5253 Introduction MCF5253 Reference Manual Rev 1 1 14 Freescale Semiconductor...
Page 62: ...Signal Description MCF5253 Reference Manual Rev 1 2 16 Freescale Semiconductor...
Page 98: ...Instruction Cache MCF5253 Reference Manual Rev 1 5 10 Freescale Semiconductor...
Page 104: ...Static RAM SRAM MCF5253 Reference Manual Rev 1 6 6 Freescale Semiconductor...
Page 128: ...Synchronous DRAM Controller Module MCF5253 Reference Manual Rev 1 7 24 Freescale Semiconductor...
Page 144: ...Bus Operation MCF5253 Reference Manual Rev 1 8 16 Freescale Semiconductor...
Page 176: ...System Integration Module SIM MCF5253 Reference Manual Rev 1 9 32 Freescale Semiconductor...
Page 198: ...Analog to Digital Converter ADC MCF5253 Reference Manual Rev 1 12 6 Freescale Semiconductor...
Page 246: ...DMA Controller MCF5253 Reference Manual Rev 1 14 18 Freescale Semiconductor...
Page 282: ...UART Modules MCF5253 Reference Manual Rev 1 15 36 Freescale Semiconductor...
Page 344: ...Audio Interface Module AIM MCF5253 Reference Manual Rev 1 17 46 Freescale Semiconductor...
Page 362: ...I2 C Modules MCF5253 Reference Manual Rev 1 18 18 Freescale Semiconductor...
Page 370: ...Boot ROM MCF5253 Reference Manual Rev 1 19 8 Freescale Semiconductor...
