PROGRAMMER
′′
S MODEL
S3C2500B
2-16
2.11 INTERRUPT LATENCIES
The worst case latency for FIQ, assuming that it is enabled, consists of the longest time the request can take to
pass through the synchroniser (
Tsyncmax
if asynchronous), plus the time for the longest instruction to complete
(
Tldm
, the longest instruction is an LDM which loads all the registers including the PC), plus the time for the data
abort entry (
Texc
), plus the time for FIQ entry (
Tfiq
). At the end of this time ARM9TDMI will be executing the
instruction at 0x1C.
Tsyncmax
is 3 processor cycles,
Tldm
is 20 cycles,
Texc
is 3 cycles, and
Tfiq
is 2 cycles. The total time is
therefore 28 processor cycles. This is just over 1.4 microseconds in a system which uses a continuous 20 MHz
processor clock. The maximum IRQ latency calculation is similar, but must allow for the fact that FIQ has higher
priority and could delay entry into the IRQ handling routine for an arbitrary length of time. The minimum latency
for FIQ or IRQ consists of the shortest time the request can take through the synchroniser (Tsyncmin) plus
Tfiq
.
This is 4 processor cycles.
2.12 RESET
When the nRESET signal goes LOW, ARM9TDMI abandons the executing instruction and then continues to fetch
instructions from incrementing word addresses.
When nRESET goes HIGH again, ARM9TDMI:
1.
Overwrites R14_svc and SPSR_svc by copying the current values of the PC and CPSR into them. The value
of the saved PC and SPSR is not defined.
2.
Forces M[4:0] to 10011 (Supervisor mode), sets the I and F bits in the CPSR, and clears the CPSR's T bit.
3.
Forces the PC to fetch the next instruction from address 0x00.
4. Execution resumes in ARM state.
Summary of Contents for S3C2500B
Page 2: ...S3C2500B 32 BIT RISC MICROPROCESSOR USER S MANUAL Revision 1 ...
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Page 80: ...PRODUCT OVERVIEW S3C2500B 1 46 NOTES ...
Page 296: ...MEMORY CONTROLLER S3C2500B 5 60 NOTES ...
Page 531: ...GDMA CONTROLLER S3C2500B 12 24 NOTES ...
Page 593: ...I O PORTS S3C2500B 15 12 NOTES ...