![](http://datasheet.mmic.net.cn/230000/79RC32438-200BB_datasheet_15568909/79RC32438-200BB_303.png)
IDT PCI Bus Interface
PCI Target
79RC32438 User Reference Manual
10 - 35
November 4, 2002
Notes
PCI DMA Channel 9 Configuration Register
Figure 10.19 PCI DMA Channel 9 Configuration Register (PCIDMA9C)
PCI Target
PCI target mode will support up to 11 queued commands. These commands can be either 11 queued
writes or 10 queued writes and one queued read. Exceeding these queue limits will result in the PCI host
transaction being retried until the command can be accepted.
The PCI target interface, shown in Figure 10.1, allows an external PCI master to read and write any
RC32438 local memory address in the same manner as the CPU core. This allows a PCI master to access
the RC32438 memory (i.e., DDR or a device) or any internal register. The PCI target interface allows PCI
masters to access 8/16/32-bit memory. The PCI target interface will automatically perform byte scattering
(writes) and gathering (reads) for devices on the memory and peripheral bus and DDR SDRAM. The PCI
target interface is expected to obey the same access and alignment rules as the CPU for accesses to
internal RC32438 registers.
The PCI bus interface provides four mapping regions from the PCI space to the RC32438’s local
address space. Each mapping region has a corresponding PCI Base Address (PBAx) register, PCI Base
Address Control (PBAxC) register, and PCI Base Address Mapping (PBAxM) register. These registers are
all part of the PCI configuration. The PBAx register corresponds to the BAR registers in the PCI 2.2 specifi-
cation. Their initial values and configuration however is controlled by the PBAxC register. The PBAxC
register holds the configuration information for the mapping region.
The Memory Space Indicator (MSI) field in a PBAxC controls how space is advertised (I/O or memory).
If the space is advertised by the MSI as memory, the Prefetchable (P) bit controls prefetching. If the space
is advertised as I/O, the Prefetchable bit is inactive. The Swap Bytes (SB) field in a PBAxC controls whether
bytes are swapped or passed unmodified between the IPBus and the PCI bus when the PCI bus interface is
accessed as a target. The PBAxM register holds the local address space base address of PCI transactions
that map to the local address space through PBAx.
The local address mapped by a PBAxM register may be any valid local address. These local addresses
are decoded in the same manner as CPU physical addresses. The local addresses mapped by one or more
PBAxM registers may be overlapping. PCI Base Addresses in PBAx registers should be non-overlapping. If
they are overlapping, one will be chosen.
PCI target burst transactions which attempt to burst data beyond the address space allocated to a PBAx
will terminate with a target disconnect without data. The PCI address spaces mapped by two PBAx regis-
ters may be contiguous. PCI target burst transactions which attempt to burst data across adjacent address
spaces mapped by PBAx registers will terminate with a target disconnect without data. The PCI Target
Control Register (PCITC) contains fields which control the behavior of the PCI bus interface when acting as
a PCI target.
MBS
Description:
Maximum Burst Size.
This field specifies the number the maximum number of words allowed in
a memory to PCI DMA operation. A value of 0x0 corresponds to 0x1000 (i.e., 4K word transfers).
Initial Value:
0x8
Read Value:
Previous value written
Write Effect:
Modify value
PCIDMA9C
0
31
12
MBS
20
0