IDT PCI Express 89HPES32NT24xG2, User Manual, Page: 293 / 744

IDT DMA Controller
PES32NT24xG2 User Manual 15 - 5 January 30, 2013
Notes
The programming of the addressing parameters must meet the following rules.
1. BCOUNT <= (SSCOUNT * SSSIZE)
2. (SSCOUNT * SSSIZE) = (DSCOUNT * DSSIZE)
An addressing operation completes execution when the byte count is exhausted or, in case the above
rules are violated, when stride addressing completes.
– When (SSCOUNT * SSSIZE) < BCOUNT, source addressing expires before the byte count
expires and the transfer terminates. The DMA may be configured to report this condition as an
error.
– When (DSCOUNT * DSSIZE) < BCOUNT, destination addressing expires before the byte count
expires and the transfer terminates. The DMA may be configured to report this condition as an
error.
Linear Addressing Example
The simplest form of DMA addressing is a linear addressing from a source address to a destination
address as shown in Figure 15.2.
Table 15.2 illustrates the parameters necessary to transfer 1 KB of data from a source address of
0x0100_0000 to a destination address of 0x0200_0001.
– BCOUNT is set to 1024 indicating the total number of bytes to transfer.
– SADDR is set to the source address 0x0100_0000 and DADDR is set to the destination address
0x0200_0001.
– Since strides are not used in this example, SSSIZE and DSSIZE are set to zero. A value of zero
indicates an infinite stride. This results in the inner loop executing in Figure 15.4 until the byte
count is exhausted.
– All stride counts (i.e., SSCOUNT and DSCOUNT) are set to one to indicate one iteration through
the outer loop.
– Since strides are not used, all stride distances (SSDIST and DSDIST) are set to zero.
A zero length linear addressing operation (i.e., one with the BCOUNT field set to zero) may be used as
a synchronization barrier. Such an operation results in a memory read request to the source address of one
DWord with no byte enables set. The operation completes when the corresponding completion is received.
No write is performed to the destination address.
– A zero length linear addressing operation may be used to ensure that data associated with
memory writes from a previous DMA descriptor operation have reached their ultimate destination
before the DMA channel is allowed to proceed.
Constant Addressing Example
By setting the stride distance to a negative value, the DMA can perform constant addressing. Constant
addressing is used to repeatedly read/write the same address(es) and is often used when moving data to/
from a memory mapped FIFO.
The parameters in Table 15.3 illustrate an example where constant addressing is used to repeatedly
read DWord data from a memory mapped FIFO and transfer (DMA) the data to a destination buffer. In this
example, there are 1024 bytes are read a DWORD at a time from the address 0x0100_0000. This operation
is graphically depicted in Figure 15.5.
BCOUNT 1024
SADDR 0x0100_0000 DADDR 0x0200_0001
SSSIZE 0 DSSIZE 0
SSCOUNT 1 DSCOUNT 1
SSDIST 0 DSDIST 0
Table 15.2 Linear Addressing DMA Example