Section 22 PCI Controller (PCIC)
SH7751 Group, SH7751R Group
Page 932 of 1128
R01UH0457EJ0301 Rev. 3.01
Sep 24, 2013
Inter-PCI Device Arbitration:
The PCI bus arbitration circuit in the PCIC can be used when the
PCIC is operating as the host device. The arbitration circuit can be connected to up to four
external PCI devices (devices that can operate as master devices) that request bus privileges.
If multiple bus privilege requests are made simultaneously by the PCI devices, the bus privilege is
grated in the predetermined order of priority. There are two orders of priority: fixed, and pseudo
round robin. The mode is selected by setting the bus master arbitration mode control bit (BMABT)
of the PCI control register (PCICR).
•
Priority-fixed mode (BMABT = 0)
In priority-fixed mode, the priority order of bus privilege requests is fixed and cannot be
changed. The order is as follows:
PCIC (device 0) > device 1 > device 2 > device 3 > device 4
That is, the PCIC has the highest order of priority and device 4 has the lowest. When bus
privilege requests occur simultaneously, the device with the highest order of priority takes
precedence. Here, device 1 is the PCI device using bus privilege request pins
PCIREQ1
and
PCIGNT1
, device 2 uses
PCIREQ2
and
PCIGNT2
, device 3 uses
PCIREQ3
and
PCIGNT3
,
and device 4 uses
PCIREQ4
and
PCIGNT4
. When the PCIC is operating as the host device, no
bus privilege request signals are output from the PCIC to the PCI bus arbitration circuit.
•
Pseudo round-robin mode (BMABT = 1)
In pseudo round-robin mode, when a device takes the bus privilege, the priority order of that
device becomes lowest.
In the initial state, the priority order is set to the same as in the fixed mode. Here, device 1
outputs a bus privilege request, after which the priority order changes to …
PCIC > device 2 > device 3 > device 4 > device 1.
If the PCIC then outputs a bus privilege request and takes the bus privilege, the priority order
changes to …
Device 2 > device 3 > device 4 > device 1 > PCIC.
Likewise, if device 3 outputs a bus privilege request and takes the bus privilege, the priority
order becomes …
Device 2 > device 4 > device 1 > PCIC > device 3.
In this way, the priority order of the master device that takes the bus privilege always changes
to lowest after the data transfer is completed.
Содержание SH7751 Group
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Страница 388: ...Section 12 Timer Unit TMU SH7751 Group SH7751R Group Page 334 of 1128 R01UH0457EJ0301 Rev 3 01 Sep 24 2013 ...
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Страница 876: ...Section 20 User Break Controller UBC SH7751 Group SH7751R Group Page 822 of 1128 R01UH0457EJ0301 Rev 3 01 Sep 24 2013 ...
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Страница 1152: ...Appendix C Mode Pin Settings SH7751 Group SH7751R Group Page 1098 of 1128 R01UH0457EJ0301 Rev 3 01 Sep 24 2013 ...
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