TAMC900 User Manual Issue 2.0.1
Page 22 of 71
Bit
DMAEN
steers the data transport into the Tracking Buffer and to the associated DMA Engine. Moreover it
controls the DMA transmission. Accordingly, if the bit is not set, no DMA transmission can be started
respectively performed. This means that e.g. in the case that the DMA Engine has been started and the
DMA enable bit is reset during operation the processing
•
of the current packet is performed but no further packets are generated,
•
all dynamic DMA information is held.
Stopping DMA transmission should only be done by using the DMAEN bit since all
information especially the one up to with memory address valid data have been placed is
visible.
The master enable is placed in the Global Channel Configuration register. If the channel is not activated
there, the channel is held in reset. This allows configuring the channel completely before activation. Thus all
changes occur concurrently and not consecutively.
The master activation of a channel causes (assuming that the channel has been configured) that
•
ADC data can be read through the register interface (*)
•
the channel’s DMA (Base) Descriptor Addresses register content is used to load DMA descriptor
information
•
DMA information (e.g. Channel DMA Buffer Fill-Level) is set in the register map
•
in dependence of the trigger mode, the QDR-II memory starts monitoring the ADC data
The asterisk marked aspect is already available after the Enable bit in the Channel Configuration register
(see below) has been set.
4.7.3 Descriptor Change
As afore-mentioned the DMA operation makes use of DMA descriptors. There is one base address
Descriptor address per channel which is used as entry point to the linked list.
Several processing flags can be set for a descriptor
before
the channel has been activated. Changes
after
activation may be destructive. Hence, only if a channel is
not
operating, a new base address can be set. This
causes a reload of the selected address.
A change of an already loaded descriptor e.g. the DMA window length will not be detected. In such a case
the base address must be assigned again or the channels need to be re-enabled.
Manipulating the content of a DMA (Base) Descriptor Addresses register while the
accompany DMA Engine is active is not allowed. Moreover changing a Descriptor in memory
during its processing is also not allowed.