
IDT DMA Controller
PES32NT24xG2 User Manual
15 - 3
January 30, 2013
Notes
The DMA supports two addressing modes: linear addressing and constant addressing. The simplest
form of DMA addressing is linear addressing. In linear addressing, a sequential block of data consisting of
BCOUNT bytes is transferred from a starting address SADDR to a destination address DADDR. Linear
addressing is graphically illustrated in Figure 15.2.
Figure 15.2 Linear Addressing
The operations performed by a DMA channel during linear addressing are shown in Figure 15.3. The
starting address of the operation along with the byte count are initialized. Data is then sequentially read or
written until the byte count is exhausted. While the operation is shown to proceed a byte at a time, blocks of
data are transferred as described in tbd. Source addressing refers to the process of reading data from
source memory while destination addressing refers to the process of writing data to the destination memory.
In this example, both source and destination addressing use linear addressing; however, this need not be
the case in general.
Figure 15.3 Linear Addressing Operations
The general addressing operations implemented by a DMA channel are shown in Figure 15.4 and the
associated parameters are described in Table 15.1. Although both the source and destination addressing
algorithms are the same, different parameter initialization may result in different behavior.
PCI Express
Memory Address
Space
BCOUNT
BCOUNT
PCI Express
Memory Address
Space
DADDR
SADDR
addr = SADDR
for (i=0; i<BCOUNT; i++) {
data = memRead(addr)
addr = addr + 1
}
addr = DADDR
for (i=0; i<BCOUNT; i++) {
memWrite(addr,data)
addr = addr + 1
}
(a) Source Addressing
(b) Destination Addressing
Содержание PCI Express 89HPES32NT24xG2
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