System Configuration and Protection
MPC561/MPC563 Reference Manual, Rev. 1.2
6-14
Freescale Semiconductor
6.1.4.4.1
Lower Priority Request Masking
This feature (if enabled) simplifies the masking of lower priority interrupt requests when a request of
certain priority is in service in applications that require interrupt nesting. The highest (pending) request is
also masked by itself. The masking is accomplished in the following way.
Upon asserting an interrupt request the BBC generates an acknowledge signal to notify the interrupt
controller that the request and the branch table offset have been latched. The interrupt controller then sets
a bit in the SISR register (interrupt in-service register), according to the asserted request. All other requests
whose priority is lower than or equal to the one that is currently in-service, become masked. The mask
remains set until the SISR bit is cleared by software (by the interrupt handler routine), writing a ‘1’ value
to the corresponding bit. The lower priority request masking diagram is presented in
.
The lower priority request masking feature is disabled by HRESET and it may be enabled by setting the
LPMASK_EN bit in the SIUMCR register.
NOTE
In the regular mode of the interrupt controller the lower priority request
masking feature is not available.
The feature must be activated only together with exception table relocation in the BBC module.
Figure 6-4. Lower Priority Request Masking—One Bit Diagram
6.1.4.4.2
Backward Compatibility with MPC555/MPC556
The enhanced interrupt controller is a feature that may be enabled according to a user’s application using
the EICEN control bit in SIUMCR register, which can be set and cleared at any time by software. If the bit
is cleared, the default interrupt controller operation is available, as described in
Interrupt Controller Operation (MPC555/MPC556-Compatible Mode)
.” The regular operation is fully
compatible with the interrupt controller already implemented in MPC555/MPC556.
illustrates the interrupt controller functionality in the MPC561/MPC563.
Enable
control bit
From bit i - 1
To bit i + 1
Set
Reset by
software
SIPEND [i]
SIMASK [i]
To RCPU
SISR[i]
generation
(OR between
all the bits)
To SIVEC
generation
IMPU
(LPMASK_EN)
Reset
External
interrupt
request
acknowledge
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...