AXI Channel Options - AXI Channel Options - 6.0 English

Enabled when there is more than one DDS channel (as opposed to AXI channel). Limited options are also available when only the PHASE channel is present. Options are:

Not Required: In this mode, no TLAST signals are present on the input PHASE channel or the output channels. In multichannel configurations, TLAST on the CONFIG channel is used to denote the last channel to be reconfigured, and is always present, regardless of this setting.
Vector Framing: A TLAST pulse on the input PHASE channel and output channels denotes the last channel in a cycle of channels (for example, 12^th of 12 channels). If the TLAST pulse is not applied at the correct time to match the channel state of the core, an event is flagged on the event_s_phase_tlast_missing or event_s_phase_tlast_unexpected event outputs.
Packet Framing: A TLAST pulse is conveyed from the input PHASE channel to the output channels with the same latency as TDATA. TLAST in this configuration can be used to trigger a reconfiguration. This mode is intended as a service to ease system design for cases where signals must accompany the datastream, but which have no application in the DDS.
Config Triggered: This option causes the core to generate an output TLAST on the last TDM channel before a new configuration is applied to the core. Subsequent output samples are generated using the new core configuration. This mode is only available when the CONFIG channel is present.

When selected, the output channels have a TREADY and hence support the AXI4handshake protocol with inherent back pressure. If there is an input PHASE channel, the presence of its TREADY is also determined by this control, so that the datapath from input PHASE channel to output channels as a whole supports back pressure or not.

The core supports two distinct uses of the TUSER field; to denote the time-division-multiplex channel index or as conduit to pass a user field (auxiliary data associated with TDATA) from input PHASE channel to output channels. These choices are independent for the input PHASE channel. However, because the selection of a user field implies the desire to convey the TUSER field from input to output, the selection of a user field on the input PHASE channel forces a user field to be present in each of the output channel TUSER ports. Options for the input PHASE channel are shown below. Options for the each output channel are constrained by the input PHASE channel choice, but are otherwise independent.

Not required: Neither of the above uses is required; the channel in question does not have a TUSER field.
Chan ID field: In this mode, the TUSER field identifies the time-division-multiplexed channel for the transfer. For the input PHASE channel, this gives the user a mechanism to synchronize to the internal DDS channel state. If the applied channel ID does not match the internal state of the core, an event is flagged on the event_s_phase_chanid_incorrect output.
User Field: In this mode, the core ignores the content of the TUSER field, but passes it unaltered from input PHASE channel to the output channels.
User and Chan ID field: In this mode the TUSER field has both a user field and a channel ID field, with the channel ID field in the least significant bits. The minimal number of bits required to describe the channel determines the width of the channel ID field; for example, seven channels require three bits.
User field width: This field determines the width of the bit field that is conveyed from input to output unaltered by the DDS. It does not include the width of the channel ID field, if it is present.

The output form is indirectly controlled by the SIN/COS Output Type parameter. When the output type is set to an integer, the two's complement and sign and magnitude options are available to the Output Form. When the output type is set to floating point, only the single precision float is available.

In general, the output of SINE and COSINE is in two's complement form. However, when quadrant symmetry is used, the output form can be changed to sign and magnitude. Selecting sign and magnitude removes the inverters following the SIN/COS LUT. This cuts resource use relative to two's complement. The single precision float behaves similarly to sign and magnitude. It is intended for use with a mixer stage where the sign information can be handled separate to the magnitude by changing the sign of the components in a complex multiplication. A mixer (complex multiplier with inputs a + jb and c + jd) can be expressed as:

Real = ac − bd

Imaginary = ad + bc

In this case, a and b from the DDS are signed, two's complement. However, if a and b are expressed as sign and magnitude, the sign from each of a and b can be used to modify the sign of each of the terms in the mixer equation. For instance, if a alone is negative, the mixer equation becomes:

Real = −ac −bd

Imaginary = −ad + bc

If the mixer stage is implemented using DSP slices, this sign manipulation can be implemented by changing the DSP48 slice opmode signal.

This selection deals with the timing of reconfiguration when both CONFIG and PHASE channels are present. The configuration channel takes configuration data asynchronously to the phase of the channel counter and stores the reconfiguration data in a buffer. This selection determines when that new configuration data takes effect on the datapath:

On Vector: In this mode, the reconfiguration data is applied when the channel counter rolls over to start a new cycle of time-division-multiplexed channels.
On Packet: In this mode, available when TLAST is set to packet framing, a TLAST on the input PHASE channel triggers the reconfiguration. This mode is targeted at cases where each set of configuration data is to be associated with the packets implied by the input TLAST indicator.

AXI Channel Options - AXI Channel Options - 6.0 English - PG141

DDS Compiler LogiCORE IP Product Guide (PG141)