System Arbitration
Élan™SC520 Microcontroller User’s Manual
8-19
maintain ownership of the CPU bus until it deasserts hb_req. The external PCI master
samples GNT0 asserted and asserts FRAME to begin the PCI transaction.
■
Clock #8: GNT0 is deasserted because either the external master is parked on the CPU
or another master has requested the bus.
■
Clock #11: The host bridge samples the end of the PCI transaction and has sampled
hb_gnt deasserted, so it deasserts hb_req to allow the next CPU bus master access to
the CPU bus.
8.4.5
Interrupts
The system arbiter has one interrupt signal routed to the ÉlanSC520 microcontroller’s PCI
host bridge. This interrupt source shares the interrupt controller input used by any PCI host
bridge interrupts that are enabled in the Host Bridge Master Interrupt Control
(HBMSTIRQCTL) register (MMCR offset 66h) register and the Host Bridge Target Interrupt
Control (HBTGTIRQCTL) (MMCR offset 62h) register.
The following condition can be programmed to generate an interrupt from the system arbiter.
■
When the PCI bus arbiter has asserted a GNT in response to a request (the bus is not
parked) and a PCI transaction was not started within 16 clocks after the bus became
idle, per the
PCI Local Bus Specification, Revision 2.2.
The GNT_TO_INT_ENB bit in the System Arbiter Control (SYSARBCTL) register (MMCR
offset 70h) is used to enable interrupts that are generated when the PCI bus arbiter detects
a grant time-out. Before the GNT_TO_INT_ENB bit is set, the PCI Host Bridge Interrupt
Mapping (PCIHOSTMAP) register (MMCR offset D14h) must be configured to route the
interrupt to the appropriate interrupt request level and priority.
The REQ/GNT number of the PCI master that did not start a transaction is reported in the
GNT_TO_STA bit of the PCI Bus Arbiter Status (PCIARBSTA) register (MMCR offset 71h).
Note that the GNT_TO_STA bit is set on PCI bus arbiter grant time-outs regardless of the
GNT_TO_INT_ENB bit value.
8.4.6
Software Considerations
The system arbiter can operate in concurrent or nonconcurrent arbitration mode (see
“Operating Modes” on page 8-3). Write posting from the CPU to the PCI bus should be
disabled while configured in nonconcurrent arbitration mode. When changing between
nonconcurrent and concurrent arbitration mode, all system arbiter requests should be
disabled, as follows:
■
GP-DMA channels should be disabled to prevent the DMA controller from requesting
the CPU bus.
■
External PCI bus master requests should be inhibited.
■
The Am5
x
86 CPU should not attempt to access the PCI bus.
A PCI bus master that does not start a transaction within 16 clocks after the bus is idle can
be considered broken. The PCI bus arbiter checks for this condition and provides status
on which PCI bus master GNT was asserted when this condition was detected. Software
can read this status and disable the broken master’s REQ to the PCI bus arbiter through
the System Arbiter Master Enable (SYSARBMENB) register (MMCR offset 72h). This
prevents the broken master from wasting PCI bandwidth.
Note that the PCI bus arbiter does not automatically disable the broken master’s REQ
signal.
Содержание Elan SC520
Страница 1: ...lan SC520 Microcontroller User s Manual Order 22004A...
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Страница 28: ...Introduction xxviii lan SC520 Microcontroller User s Manual...
Страница 42: ...Architectural Overview 1 14 lan SC520 Microcontroller User s Manual...
Страница 78: ...System Initialization 3 22 lan SC520 Microcontroller User s Manual...
Страница 108: ...Clock Generation and Control 5 10 lan SC520 Microcontroller User s Manual...
Страница 118: ...Reset Generation 6 10 lan SC520 Microcontroller User s Manual...
Страница 148: ...System Arbitration 8 24 lan SC520 Microcontroller User s Manual...
Страница 214: ...SDRAM Controller 10 36 lan SC520 Microcontroller User s Manual...
Страница 230: ...Write Buffer and Read Buffer 11 16 lan SC520 Microcontroller User s Manual...
Страница 288: ...GP Bus DMA Controller 14 22 lan SC520 Microcontroller User s Manual...
Страница 316: ...Programmable Interval Timer 16 8 lan SC520 Microcontroller User s Manual...
Страница 328: ...Software Timer 18 4 lan SC520 Microcontroller User s Manual...
Страница 346: ...Real Time Clock 20 12 lan SC520 Microcontroller User s Manual...
Страница 360: ...UART Serial Ports 21 14 lan SC520 Microcontroller User s Manual...
Страница 414: ...AMDebug Technology 26 8 lan SC520 Microcontroller User s Manual...