PCI Bus Host Bridge
Élan™SC520 Microcontroller User’s Manual
9-23
Figure 9-14
External PCI Bus Master Posted Write to SDRAM
The following sequence annotates the external PCI bus master posted write to SDRAM
shown in Figure 9-14.
■
Clock #1: An external PCI master initiates a write transaction to the ÉlanSC520
microcontroller’s SDRAM.
■
Clock #3: The PCI host bridge always asserts DEVSEL with medium timing. In this
example, the write FIFO is not full, so TRDY is also asserted to accept the write data.
If either the write FIFO or the address FIFO had been full, then the PCI host bridge would
immediately issue a retry to the external master by asserting STOP instead of TRDY.
■
Clocks #4–#10: The write FIFO is not full, so TRDY remains asserted to accept the
write data. The PCI host bridge does not insert wait states into the PCI transaction by
deasserting TRDY. If the FIFO becomes full during the transaction but the external PCI
master indicates it is willing to burst more data (by keeping FRAME asserted), the host
bridge issues a disconnect by deasserting TRDY and asserting STOP (see
Section 9.5.4.9.3). The external master can insert wait states into the PCI transaction
by deasserting IRDY. The host bridge is posting the write data (it will be written to SDRAM
sometime later).
■
Clock #7: The PCI host bridge has synchronized the first PCI data phase (Clock #4)
and requests access to the SDRAM controller.
■
Clock #9: The SDRAM controller is granted to the PCI host bridge and the PCI bus data
can be written to SDRAM. The hb_gnt signal may be delayed if the Am5
x
86 CPU or GP-
DMA is accessing SDRAM.
1
2
3
4
5
6
7
8
9
10
address
data1
data2
data3
write cmd
be1
be2
be3
data4
be4
data5
data6
data7
be5
be6
be7
CLKPCIIN
ADx
CBEx
FRAME
IRDY
TRDY
DEVSEL
hb_req
hb_gnt
Notes:
The diagram includes the following internal signals:
• hb_req: PCI host bridge requesting the Am5
x
86 CPU bus to access the SDRAM controller.
• hb_gnt: PCI host bridge has been granted Am5
x
86 CPU bus and can access the SDRAM controller.
See Chapter 8, “System Arbitration”, for information on Am5
x
86 CPU bus arbitration.
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...