MOTOROLA
INTEGER CPU
MMC2001
2-4
REFERENCE MANUAL
The alternate file is selected for use via a control bit in the PSR. The status, control,
and scratch registers are accessed via the move from control register (mfcr) and
move to control register (mtcr) instructions. When the alternate file is selected via the
AF bit in the PSR, general-purpose operands are accessed from it. When the AF bit
is cleared, operands are accessed from the normal file. This alternate file is provided
to allow very low overhead context switching capability for real-time event handling.
Figure 2-1 Programming Model
The supervisor programming model includes the PSR, which contains operation con-
trol and status information. In addition, a set of exception shadow registers is pro-
vided to save the state of the PSR and the program counter at the time an exception
occurs. A separate set of shadow registers is provided for fast interrupt support to
minimize context saving overhead.
Five scratch registers are provided for supervisor software use in handling exception
events. A single register is provided to alter the base address of the exception vector
table. Two registers are provided for global control and status.
R0
R1
R2
R3
R4
R5
R6
R7
R8
R9
R12
R13
R14
R15
R11
R10
C
R0’
R1
R2
R3
R4
R5
R6
R7
R8
R9
R12
R13
R14
R15
R11
R10
R0
R1
R2
R3
R4
R5
R6
R7
R8
R9
R12
R13
R14
R15
R11
R10
User Programmer’s
Model
Alternate file
Supervisor Programmer’s
Model
PC
PC
C
* bit 0 of PSR
PSR
VBR
EPSR
FPSR
EPC
FPC
SS0
SS1
SS2
CR0
CR1
CR2
CR3
CR4
CR5
CR6
CR7
CR8
CR9
SS4
CR10
GCR
CR11
SS3
GSR
CR12
Freescale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
nc.
..