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Enhanced Time Processing Unit (eTPU2)
Freescale Semiconductor
29-81
PXR40 Microcontroller Reference Manual, Rev. 1
29.4.2.3.3
Channel Number Priority
If more than one channel of a priority level is requesting service, the lowest numbered channel is granted
service first. For example, if channels 0, 5, and 9 are all high-level channels requesting service during a
high time slot, channel 0 is granted service first. Continuing this example, if channel 0 requests service
again immediately after being serviced, it is not serviced again until channels 5 and 9 are serviced. This
scheme is implemented so that continuously-requesting low numbered channels do not take all the time on
the eTPU execution unit and leave no time for other channels.
The scheduler uses registers to keep track of which channels have been serviced and which require
servicing. Each channel has two register bit: a service request register (SRR) and a service grant register
(SGR). The SRR is set when a channel requests service. After the channel has been granted service, the
SGR is set and the SRR is cleared.
SGRs are not cleared individually by channel, but rather as priority level groups. The clearing of a group
of SGRs begins a new cycle for that priority level. An SGR group is cleared on the condition that a channel
of that priority level has just been serviced, and no other channel of that priority level is requesting service
(has a set SRR) and has not been granted service (has a clear SGR).
For example, if a middle-priority channel has just been serviced (either in a middle-priority time slot or a
high or low-priority time slot gained by priority passing), the SRRs and SGRs of all middle-priority
channels are compared. If there is no middle-priority channel with its SRR set and SGR cleared, the
scheduler clears all middle-level SGRs. If there is a middle-level channel with its SRR set and SGR
cleared, the scheduler does not clear the SGR group, and the requesting middle-level channel is serviced
on the next middle-level time slot (or possibly sooner by priority passing).
29.4.2.3.4
SDM Collision Rate
Most function threads read or write to the eTPU SDM at least once. Because both the eTPU Microengine
and Host can access the SDM but not at the same time, the Microengine may suspend execution during the
SDM access while waiting for the Host to finish accessing the SDM. At other times the Host may wait for
the Microengine. Wait states can take up to two eTPU clocks, when the Host accesses the SDM directly,
without using CDC. Microengine(s) wait-states must be added into the worst-case latency calculation. The
system designer should estimate the percentage of SDM accesses in the system that will result in
Microengine wait-states. This percentage is called the RAM collision rate (RCR). In each collision with
direct Host accesses to the SDM the Microengine(s) wait for two eTPU clocks.
In eTPU the Coherent Dual-parameter Controller (CDC) may also access the SDM for atomic transfers of
two parameters. eTPU Microengine may wait on this operation (if it is in service time) until the transfer is
complete. CDC always transfers two parameters, making four consecutive accesses (read, write, read,
write) of one eTPU clock each. The system designer should estimate the percentage of SDM accesses in
the system that will result in a Microengine wait due to coherent transfer, and multiply it with the average
number of eTPU clocks the Microengine waits for each transfer. This percentage is called Coherent
Parameter Collision Rate (CPCR).
In addition, Microengine to Microengine multiple parameter coherent communication, using the hardware
semaphores, may hold one Microengine which waits to lock the semaphore while the other Microengine
is holding it. This waiting is due to a software loop, not hardware wait-states. Note that single parameter
access of one Microengine does not affect the timing of the other Microengine due to SDM time interlace.
Содержание PXR4030
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Страница 120: ...Signal Descriptions 3 54 Freescale Semiconductor PXR40 Microcontroller Reference Manual Rev 1...
Страница 158: ...Power Management Controller PMC 5 26 Freescale Semiconductor PXR40 Microcontroller Reference Manual Rev 1...
Страница 182: ...Frequency Modulated Phase Locked Loop FMPLL 6 24 Freescale Semiconductor PXR40 Microcontroller Reference Manual Rev 1...
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Страница 496: ...Error Correction Status Module ECSM 17 18 Freescale Semiconductor PXR40 Microcontroller Reference Manual Rev 1...
Страница 524: ...Periodic Interrupt Timer PIT_RTI 20 12 Freescale Semiconductor PXR40 Microcontroller Reference Manual Rev 1...
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