PCI Bus Host Bridge
9-24
Élan™SC520 Microcontroller User’s Manual
9.5.4.9.2
External PCI Master SDRAM Read (Delayed Transaction)
Figure 9-15 shows an external PCI bus master read transaction to the ÉlanSC520
microcontroller’s SDRAM.
Figure 9-15
External PCI Master SDRAM Read (Delayed Transaction)
The following sequence annotates the external PCI master SDRAM read shown in
Figure 9-15.
■
Clock #1: An external PCI bus master initiates a read transaction to ÉlanSC520
microcontroller’s SDRAM.
■
Clock #3: The PCI host bridge target controller accepts the transaction by asserting
DEVSEL. TRDY is not asserted, because there is no data in the target read FIFO (this
is a new transaction).
■
Clock #4: The PCI host bridge target controller asserts STOP, signaling a retry to the
external PCI bus master. Because no data was transferred, the external PCI bus master
is required to retry the transaction. (This figure assumes that the ÉlanSC520
microcontroller is configured for automatic delayed transactions.) The host bridge
latches the transaction information and will prefetch the requested read data. This is
now a delayed transaction, and the PCI bus master is required to relinquish bus
ownership and re-arbitrate to retry the cycle. If there is already a previous delayed
transaction pending, the current transaction will not be latched. Note that, in this example,
STOP is asserted for two clock periods, because a target is required to keep this signal
asserted until FRAME is deasserted.
■
Clock #7: The PCI host bridge has synchronized the delayed transaction request and
requests access to the SDRAM controller to prefetch the data requested by the external
PCI master.
■
Clock #8: The CPU bus is granted to the PCI host bridge, and the PCI bus data can be
read from SDRAM. The hb_gnt signal may be delayed if the Am5
x
86 CPU or GP-DMA
controller is accessing SDRAM. The host bridge prefetches up to the next cache line in
response to a memory-read or memory-read-line command and up to 64 doublewords
in response to a memory-read-multiple command.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
FPG
EH
DGGUHV
V
DGGUHVV
FPG
GDWD
GDWD
GDWD
EH
EH EH
CLKPCIIN
ADx
CBEx
FRAME
IRDY
TRDY
DEVSEL
STOP
hb_req
hb_gnt
Содержание Elan SC520
Страница 1: ...lan SC520 Microcontroller User s Manual Order 22004A...
Страница 4: ...iv lan SC520 Microcontroller User s Manual...
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...