Run-Time Parameter Specification - 2022.1 English

Vitis Model Composer User Guide (UG1483)

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2022.1 English

It is possible to modify the behavior of the AI Engine program or data-flow graph based on a dynamic condition or event using the run-time parameter. The modification could be in the data being processed, for example a modified mode of operation or a new coefficient table, or it could be in the control flow of the graph such as conditional execution or dynamically reconfiguring a graph. Either the kernels or the graphs can be defined to execute with parameters.

If an integer scalar value appears in the formal arguments of a kernel function, then that parameter becomes a run-time parameter. Run-time parameters are processed as ports alongside those created by streams and windows. Both scalar and array values can be passed as run-time parameters.

Consider the following example where a kernel function is defined with run-time parameters. Here, select is a scalar RTP port and coefficients is a vector RTP with 32 integers.

#ifndef RTP_KERNEL_H
#define RTP_KERNEL_H
void simple_param(input_window_cint16 * in,
                  output_window_cint16 *outw,
                  int select,
                  const int32 (&coefficients)[32]);
Two types of RTPs are supported:
Synchronous Parameters (or triggering parameters)
The kernel does not execute until the run-time parameter is written by a controlling processor. Upon a write, the kernel executes once, reading the new updated value. After completion, it is blocked from executing again until the parameter is updated. This allows for a different type of execution model from the normal streaming model, and can be useful for certain updating operations where blocking synchronization is important.
Asynchronous Parameters
These parameters can be changed any time by either a controlling processor such as ArmĀ® . They are read each time a kernel is invoked without any specific synchronization. These types of parameters can be used, for example, to pass new filter coefficients to a filter kernel that changes infrequently.