The kernel interfaces are used to exchange data with the host application,
other kernels, or device I/Os. Both user-managed and XRT-managed have exactly the same
interface requirements as listed here:
- Programmable interface
-
AXI4-Lite slave interface. Kernels can only
have a single AXI4-Lite interface.
- Data interfaces
- Any number and combination of AXI4 memory
mapped and AXI4-Stream interfaces.
- Clock and resets
- As described in Clock and Reset Requirements.
Tip: XRT-managed kernels have
specific requirements for control registers in the
AXI4-Lite interface (including start and stop bits) as described in
Control Requirements for XRT-Managed Kernels. User-managed kernels can implement
whatever control scheme the user specifies.
The following table elaborates the type of interface required based on
the characteristics of the data movement in your application.
Table 1. Kernel Interface Types
| Register (AXI4-Lite) |
Memory Mapped (M_AXI) |
Streaming (AXI4-Stream) |
- Register interfaces must be implemented using a
single AXI4-Lite
interface.
- Designed for transferring scalars between the
host application and the kernel.
- Register reads and writes are initiated by the host application.
- The kernel acts as a slave.
|
- Memory mapped interfaces must be implemented
using one or more AXI4
Masters interfaces.
- Designed for bi-directional data transfers with global memory (DDR,
PLRAM, HBM).
- Introduces additional latency for memory
transfers.
- The kernel acts as a master accessing data
stored into global memory.
- The host application allocates the buffer for
the size of the dataset.
- The base address of the buffer is provided by the host application to
the kernel via the AXI4-Lite
interface.
|
- Streaming interfaces must be implemented using
one or more AXI4-Stream
interfaces.
- Designed for uni-directional data transfers
between kernels.
- The access pattern is sequential.
- Does not use global memory.
- Data set is unbounded.
- A sideband signal can be used to indicate the
last value in the stream.
|