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Interrupt Controller (CF1_INTC)
MCF51CN128 Reference Manual, Rev. 6
Freescale Semiconductor
8-17
8.4
Functional Description
The basic operation of the CF1_INTC is detailed in the preceding sections. This section describes special
rules applicable to non-maskable level seven interrupt requests and the module’s interfaces.
8.4.1
Handling of Non-Maskable Level 7 Interrupt Requests
The CPU treats level seven interrupts as non-maskable, edge-sensitive requests, while levels one through
six are maskable, level-sensitive requests. As a result of this definition, level seven interrupt requests are
a special case. The edge-sensitive nature of these requests means the encoded 3-bit level input from the
CF1_INTC to the V1 ColdFire core must change state before the CPU detects an interrupt. A
non-maskable interrupt (NMI) is generated each time the encoded interrupt level changes to level seven
(regardless of the SR[I] field) and each time the SR[I] mask changes from seven to a lower value while the
encoded request level remains at seven.
8.5
Initialization Information
The reset state of the CF1_INTC module enables the default IRQ mappings and clears any software-forced
interrupt requests (INTC_FRC is cleared). Immediately after reset, the CF1_INTC begins its
cycle-by-cycle evaluation of any asserted interrupt requests and forms the appropriate encoded interrupt
level and vector information for the V1 Coldfire processor core. The ability to mask individual interrupt
requests using the interrupt controller’s IMR is always available, regardless of the level of a particular
interrupt request.
8.6
Application Information
This section discusses three application topics: emulation of the HCS08’s one level interrupt nesting
structure, elevating the priority of two IRQs, and more details on the operation of the software interrupt
acknowledge (SWIACK) mechanism.
8.6.1
Emulation of the HCS08’s 1-Level IRQ Handling
, the HCS08 architecture specifies a 1-level IRQ nesting capability. Interrupt masking
is controlled by CCR[I], the interrupt mask flag: clearing CCR[I] enables interrupts, while setting CCR[I]
Table 8-12. INTC_SWIACK, INTC_LVL
n
IACK Field Descriptions
Field
Description
7
Reserved, must be cleared.
6–0
VECN
Vector number. Indicates the appropriate vector number.
For the SWIACK register, it is the highest-level, highest-priority request currently being asserted in the CF1_INTC
module. If there are no pending requests, VECN is zero.
For the LVL
n
IACK register, it is the highest priority request within the specified level-
n
. If there are no pending
requests within the level, VECN is 0x18 (24) to signal a spurious interrupt.