VHDL Source: olo_base_dyn_sft
This entity implements a dynamic shift (barrel shift) implemented in multiple stages in order to achieve good timing. The number of bits to shift can be selected at runtime for each data-sample.
| Name | Type | Default | Description |
|---|---|---|---|
| Width_g | positive | - | Data width |
| Direction_g | string | - | Direction to shift. Allowed values are "LEFT" (shift towards MSB) and "RIGHT" (shift towards LSB). |
| MaxShift_g | positive | - | Maximum number of bits to shift. MaxShift_g must be smaller or equal to Width_g. |
| SignExtend_g | boolean | false | Controls whether the sign bit is replicated (true) or zeros are shifted in (false) for Direction_g = "LEFT". true is used to perform arithmetic left-shifts for signed numbers. |
| SelBitsPerStage_g | positive | 4 | Number of bits from In_Shift to implement in each stage. This parameter controls how many pipeline stages are implenented: Stages = ceil(log2(MaxShift_g+1))/SelBitsPerStage Smaller values lead to better timing performance, bigger values to less stages (less latency). |
| Name | In/Out | Length | Default | Description |
|---|---|---|---|---|
| Clk | in | 1 | - | Clock |
| Rst | in | 1 | - | Reset input (high-active, synchronous to Clk) |
| Name | In/Out | Length | Default | Description |
|---|---|---|---|---|
| In_Data | in | Width_g | - | Input data |
| In_Shift | in | ceil(log2(MaxShift_g+1)) | - | Number of bits to shift the corresponding In_Data sample. |
| In_Valid | in | 1 | '1' | AXI4-Stream handshaking signal for In_Data |
| Name | In/Out | Length | Default | Description |
|---|---|---|---|---|
| Out_Data | out | Width_g | N/A | Output data |
| In_Valid | out | 1 | '1' | AXI4-Stream handshaking signal for Out_Data |
Below figure shows the implementation for MaxShift_g=15 and SelBitsPerStage_g=2.
For example a shift by 7 bits is implemented as shift by 3 bits in the first stage plus shift by 4 bits in the second stage.
