Importing an AI Engine Kernel with Runtime Parameters - 2024.1 English

Vitis Model Composer User Guide (UG1483)

Document ID
Release Date
2024.1 English

Vitis Model Composer supports importing AI Engine kernels with runtime parameters in kernel functions alongside window and stream types. The following table lists the scalar data types that can be passed as runtime parameters.

Table 1. Scalar Data Types
<Type> Complexity Signedness
int8 Real Signed
int16 Real Signed
int32 Real Signed
int64 Real Signed
uint8 Real Unsigned
uint16 Real Unsigned
uint32 Real Unsigned
uint64 Real Unsigned
cint16 Complex Signed
cint32 Complex Signed
float Real N/A
cfloat Complex N/A
bfloat16 Real N/A

Implicit ports are inferred for each parameter (scalar and vector data types) in the function argument. The following table describes the type of port inferred for each function argument.

Formal Parameter Port Class
T Input
Const T Input
T & Inout
Const T & Input
Const T (&) [ .. ] Input
T (&)[ .. ] Inout

In the following example, the simple_rtp function has two real-time parameters. Notice the function argument select which is passed by value, and argument weight which is passed by reference.

#ifndef __RTP_KERNEL_H__
#define __RTP_KERNEL_H__
void simple_rtp(input_buffer<cint16> & in,output_buffer<cint16> & outw, int32 &weight, int32 select);
#endif //__RTP_KERNEL_H__

When imported for the above function, the AIE Kernel block looks as shown in the following figure. In Model Composer, the inout port appears as the output port on the AIE Kernel block.

Note: Vitis Model Composer ignores the inout RTP ports during code generation and only considers them for Simulink simulation. (that is, they will not be read from the PS).

Because RTPs are used alongside the window and stream ports, the procedure for importing the kernel function remains the same. When the above kernel function with RTPs are imported, the AIE Kernel block looks as shown in the following figure.

Figure 1. AIE Kernel (RTPs) Generated by Your Tool
Note: The AIE kernel block name (simple_rtp) is the same as the AI Engine kernel function name.

After a successful import, the Function tab displays automatically. You can quickly review the function definition and runtime parameter ports as shown.

Figure 2. Function Tab

Port synchronicity is the only parameter that is specific to RTPs. The following table provides details about the valid synchronicity of the Destination RTP input port with respect to the Source RTP inout port. The default port synchronicity is set to 'auto'.

Table 2. Valid Synchronicity
Source RTP Inout Port Destination RTP input Port
auto async
sync auto
sync sync
async async

If the source RTP inout port is set to 'auto' then the destination RTP input port should be 'async'. Similarly for other combinations. Model Composer throws an appropriate error when you try to use any combination which is not specified in the previous table.