A.5.1. Reviewing Component Interfaces
The Component Viewer shows a visual representation of the interfaces in your component. You can view details about the following interface arguments: default, pointer, pass-by-reference, Avalon® Memory-Mapped (MM), and Avalon® Streaming.
Some interface arguments in your component can be marked as being stable. A stable interface argument is an argument that does not change while your component executes, but the argument might change between component executions. In the Component Viewer, a stable node does not have any edge connection.
The Component Viewer displays the different interfaces as outlined in the following sections:
Default Interface Arguments
Default interface arguments are any scalars or simple structs. The Component Viewer connects the default argument nodes to the corresponding channel read (RD) node.
#include "HLS/hls.h"
#include "stdio.h"
struct coordinate_t {
int x;
int y;
};
component int default_comp(int b, coordinate_t p) {
return b + p.x;
}
For each default interface argument node, you can view details about the node when you hover over the node:
Pointer, Pass-By-Reference, and Avalon® MM Master Interface Arguments
Pointer interfaces, pass-by-reference interfaces, Avalon® MM master interfaces, and global variables all correspond to addresses to memory outside of your component. Similarly to the default interface arguments, these nodes connect to the corresponding channel read (RD) node for your component.
#include "HLS/hls.h"
#include "stdio.h"
component int master_comp(
int *pointer_d,
ihc::mm_master<int, ihc::aspace<3>, ihc::awidth<4>, ihc::dwidth<32>,ihc::latency<1>, ihc::align<4> > &master_i,
int &result
)
{
result = *pointer_d + *master_i;
return result;
} 
The Component Viewer shows the following details for these interface arguments:
- Stable
- Describes whether the interface argument is stable. That is, whether the hls_stable_argument attribute was applied.
- Data width
- The width of the memory-mapped data bus in bits.
- Address width
- The width of the memory-mapped address bus in bits.
- Latency
- The guaranteed latency from when the read command exits the component to when the external memory returns valid read data. The latency is measured in clock cycles.
- Maximum burst
- The maximum number of data transfers that can associate with a read or write transaction. For fixed latency interfaces, this value is set to 1.
- Alignment
- The byte alignment of the base pointer address. The Intel® HLS Compiler uses this information to determine the amount of coalescing that is possible for loads and stores to this pointer.
The Component Viewer shows the following details for global memories:
- Memory address space number
- The memory address space number for global memory.
- Number of banks
- The number of memory banks contained in the memory.
- Argument Name:
- The names of arguments that access the global memory.
Avalon® MM Slave Register Interface Arguments
When you label an interface argument as an Avalon® MM slave register (hls_avalon_slave_register_argument), then the interface argument is implemented in the control and status register (CSR) slave interface. The Component Viewer puts the slave register arguments inside a CSR container.
#include "HLS/hls.h"
#include "stdio.h"
component int slavereg_comp(
int hls_avalon_slave_register_argument slave_scalar_f,
int* hls_avalon_slave_register_argument slave_pointer_g
) {
return slave_scalar_f + *slave_pointer_g;
} 
The resulting memory map is described in the automatically generated header file <component_name>_csr.h. This header file is available in the menu in the source code pane. Clicking on the CSR container node in the Component Viewer also opens up the header file:
If you use the hls_avalon_slave_component macro, then the “do” and “return” streams (control and status registers) are implemented in the CSR interface:
#include "HLS/hls.h"
#include "stdio.h"
hls_avalon_slave_component
component int slavereg_comp(
int hls_avalon_slave_register_argument slave_scalar_f,
int* hls_avalon_slave_register_argument slave_pointer_g
) {
return slave_scalar_f + *slave_pointer_g;
}Avalon® MM Slave Memory Interface Arguments
When you declare a pointer argument as a slave memory, the Component Viewer shows the slave memory interface with a <slave memory name> LD/ST node that is connected to the Local Memory node in the component.
#include "HLS/hls.h"
#include "stdio.h"
hls_avalon_slave_component
component int slavemem_comp(
hls_avalon_slave_memory_argument(4096) int* slave_mem_h,
int index,
int hls_avalon_slave_register_argument slave_scalar_f
) {
return slave_mem_h[index] * slave_scalar_f;
} 
If you look at the same Avalon® MM slave memory interface in the Component Memory Viewer report, the same <slave memory name> LD/ST node is shown to be connected to an external RW port.
Avalon® Streaming Interface Arguments
A streaming interface is shown in the Component Viewer by a <stream name> node connected to the corresponding RD node (for stream_in<>) or WR node (for stream_out<>).
#include "HLS/hls.h"
#include "stdio.h"
component int stream_comp(
ihc::stream_in<int> &stream_in_c,
ihc::stream_out<int> &stream_out_e,
int scalar_b
) {
stream_out_e.write(scalar_b + 1);
return stream_in_c.read() + scalar_b * 2;
}
The Component Viewer shows the following details for streaming interface arguments:
- Width
- The width of the data bus in bits.
- Depth
-
The depth of the stream in words
The word size of the stream is the size of the stream datatype.
- Bits per symbol
- Describes how the data is broken into symbols on the data bus.
- Uses Packets
- Indicates whether the interface exposes the startofpacket and endofpacket sideband signals on the stream interfaces. The signals can be access by the packet-based reads and writes.
- Uses Valid
- (stream_in) Indicates whether a valid signal is present on the stream interface. When Yes, the upstream source must provide valid data on every cycle that ready is asserted.
- Uses Reader
- (stream_in) Indicates whether a ready signal is present on the stream interface. When Yes, the downstream sink must be able to accept data on every cycle that valid is asserted.
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