
S3C8248/C8245/P8245/C8247/C8249/P8249
INTERRUPT STRUCTURE
5-15
INTERRUPT SOURCE POLLING SEQUENCE
The interrupt request polling and servicing sequence is as follows:
1.
A source generates an interrupt request by setting the interrupt request bit to "1".
2.
The CPU polling procedure identifies a pending condition for that source.
3.
The CPU checks the source's interrupt level.
4.
The CPU generates an interrupt acknowledge signal.
5.
Interrupt logic determines the interrupt's vector address.
6.
The service routine starts and the source's pending bit is cleared to "0" (by hardware or by software).
7.
The CPU continues polling for interrupt requests.
INTERRUPT SERVICE ROUTINES
Before an interrupt request is serviced, the following conditions must be met:
— Interrupt processing must be globally enabled (EI, SYM.0 = "1")
— The interrupt level must be enabled (IMR register)
— The interrupt level must have the highest priority if more than one levels are currently requesting service
— The interrupt must be enabled at the interrupt's source (peripheral control register)
When all the above conditions are met, the interrupt request is acknowledged at the end of the instruction cycle.
The CPU then initiates an interrupt machine cycle that completes the following processing sequence:
1.
Reset (clear to "0") the interrupt enable bit in the SYM register (SYM.0) to disable all subsequent interrupts.
2.
Save the program counter (PC) and status flags to the system stack.
3.
Branch to the interrupt vector to fetch the address of the service routine.
4.
Pass control to the interrupt service routine.
When the interrupt service routine is completed, the CPU issues an Interrupt Return (IRET). The IRET restores
the PC and status flags, setting SYM.0 to "1". It allows the CPU to process the next interrupt request.
Summary of Contents for C8245
Page 31: ...ADDRESS SPACES S3C8248 C8245 P8245 C8247 C8249 P8249 2 20 NOTES ...
Page 107: ...INTERRUPT STRUCTURE S3C8248 C8245 P8245 C8247 C8249 P8249 5 18 NOTES ...
Page 195: ...INSTRUCTION SET S3C8248 C8245 P8245 C8247 C8249 P8249 6 88 NOTES ...
Page 221: ...I O PORTS S3C8248 C8245 P8245 C8247 C8249 P8249 9 16 NOTES ...
Page 245: ...16 BIT TIMER 0 1 S3C8248 C8245 P8245 C8247 C8249 P8249 12 10 NOTES ...
Page 249: ...WATCH TIMER S3C8248 C8245 P8245 C8247 C8249 P8249 13 4 NOTES ...
Page 267: ...A D CONVERTER S3C8248 C8245 P8245 C8247 C8249 P8249 15 6 NOTES ...
Page 299: ...S3P8245 P8249 OTP S3C8248 C8245 P8245 C8247 C8249 P8249 21 8 NOTES ...
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