
TAMC900 User Manual Issue 2.0.1
Page 23 of 71
4.7.4 Channel Start/Stop
There are some constraints on the configurability of a channel in context of its channel group initially
mentioned in this chapter. Additionally, the channel start conditions for data processing are summarized
afterwards.
The DMA operation can be performed if
•
DMA operation is enabled
•
a valid DMA descriptor is defined and loaded
•
the associated QDR-II memory is ready for use
•
the Channel Group Trigger is configured
•
the channel itself (channel configuration) is enabled
•
the channel’s global control bits are set
If one condition is not met, the corresponding channel cannot be used.
Besides these conditions it has to be considered that the QDR-II memories have been filled with valid data
as far as required for Pre-Trigger Data Gathering if used.
An active channel is stopped automatically if its associated Linked List has been processed. Stopping the
processing while it is running (if necessary) should be done via the DMA Enable Bit (see chapter “Channel
Activation”).
Since the channels are handled concurrently the length of the channel DMA windows is
defined separately. Consequently, one channel can still be active while the others the group
have already finished.
4.8 Restrictions
4.8.1 Processing Limit
The PCI Express adaptation is currently limited to 1 GByte/sec. Due to header overhead a fraction of
approximately 88.89% (888 MByte/sec) can be
continuously
transmitted via the module. Exceeding this
limitation causes the DMA processing to stop after the internal buffer structure has collapsed.
For all channels at least 256 k samples can be obtained independently of the transmission rate caused by
the integration of the QDR-II memory in the transmission path (refer chapter “Tracking Buffer”).
The amount of data can be composed over all channels.