2-32
Functional Description
2.10.5 Masking and Enabling Interrupts
lists the registers used for masking and enabling interrupts. For
testing purposes, certain types of interrupts can be forced by writing
individual bits in the
register (
). These
interrupts can be masked by clearing the corresponding bit in the
register (
). Even if the interrupt is masked,
the corresponding bit in the ISR will be set if the interrupting condition
occurs.
Masking an interrupt prevents it from being seen by the microcontroller
core in the SYM53C040. You can allow hardware interrupts either by
enabling them in the appropriate register bits, or by masking the
interrupts and polling for them. In general, it is recommended to enable
as few interrupts as possible and mask/poll for them instead. With the
microcontroller and the serial transfer rates on the Two-Wire Serial bus,
masking and polling for interrupts is less disruptive to the microcontroller
and does not impede performance. An exception to this recommendation
would be SCSI and 8067 interrupts, since the bus speeds and the need
to complete transfers quickly suggest that interrupts should be enabled.
2.10.6 Polling and Hardware Interrupts
The microcontroller core is informed of an interrupt condition by polling
or hardware interrupts. Polling means that the microcontroller must
continually loop and read a register until it detects a bit set that indicates
an interrupt. This method is the fastest, but consumes microcontroller
time that could be used for other tasks. The other method for detecting
interrupts is hardware interrupts, where the interrupting condition asserts
one of the microcontroller external interrupt signals. This interrupts the
microcontroller, and causes it to execute an interrupt service routine. A
hybrid approach is common, using hardware interrupts for conditions that
might occur infrequently or after a long wait; and polling for interrupts that
typically occur after only a short wait.
2.10.7 Interrupt Service Routine
When the microcontroller core receives an interrupt, it reads the
register (
) to determine the source of the interrupt.
Once it determines the source of the interrupt, it reads the appropriate
Содержание Symbios SYM53C040
Страница 12: ...xii Preface...
Страница 90: ...4 18 SCSI and DMA Registers...
Страница 98: ...5 8 SFF 8067 Registers...
Страница 110: ...6 12 Two Wire Serial Registers...
Страница 126: ...7 16 Miscellaneous Registers...
Страница 160: ...8 34 System Registers...
Страница 184: ...9 24 Electrical Characteristics...
Страница 194: ...A 10 Register Summary...
Страница 214: ......