ADLINK PCIe-9814 - Manual (Page 26)

16 Operations
being limited by memory limitations. In non-scatter-gather mode,
the maximum DMA data transfer size is 2 MB double words (8 MB
bytes); in scatter-gather mode, there is no limitation on DMA data
transfer size except the physical storage capacity of the system.
Users can also link descriptor nodes circularly to achieve a multi-
buffered DMA. Figure 3-2 illustrates a linked list comprising three
DMA descriptors. Each descriptor contains a PCI address, PCI
dual address, a transfer size, and the pointer to the next descrip-
tor. PCI address and PCI dual address support 64-bit addresses
which can be mapped into more than 4 GB of address space, but
the subsequent descriptor address must be less than 4GB.
Figure 3-2: Linked List of PCI Address DMA Descriptors
3.2.4 Synchronous Digital Input
The PCIe-9814 has three synchronous digital input channels,
SDI0, SDI1 and SDI1. These three digital input lines can be sam-
pled synchronously with the Timebase clock for mixed signal
applications. Thus the data transfer can reach 80 Mbit/s when
using internal 80 MS/s Timebase clock. These three digital input
lines are combined with ADC data and located in 3 LSB when SDI
function is enabled, as shown.
Local Memory
( FIFO)
PCI Express Bus
First PCI Address
First Dual Address
Transfer Size
Next Descriptor
PCI Address
Dual Address
Transfer Size
Next Descriptor
PCI Address
Dual Address
Transfer Size
Next Descriptor