As discussed in Linking the System,
there are a number of --connectivity.XXX
options that
let you define the topology of the FPGA binary, specifying the number of CUs, assigning
them to SLRs, connecting kernel ports to global memory, and establishing streaming port
connections. These commands are an integral part of the build process, critical to the
definition and construction of the application.
--connectivity.nk
--connectivity.nk <arg>
Where <arg>
is specified
as <kernel_name>:#:<cu_name1>,<cu_name2>,...<cu_name#>
.
This instantiates the specified number of CU (#
) for the specified kernel (kernel_name
) in the generated FPGA binary (.xclbin
) file during the linking process. The cu_name
is optional. If the cu_name
is not specified, the instances of the kernel are simply
numbered: kernel_name_1
, kernel_name_2
, and so forth. By default, the Vitis compiler instantiates one compute unit for
each kernel.
For example:
v++ --link --connectivity.nk vadd:3:vadd_A,vadd_B,vadd_C
[connectivity]
section head using the following
format:[connectivity]
nk=vadd:3:vadd_A,vadd_B,vadd_C
--connectivity.sc
--connectivity.sc <arg>
Create a streaming connection between two compute units through
their AXI4-Stream interfaces. Use a separate
--connectivity.sc
option for each streaming
interface connection. The order of connection must be from a streaming output port
of the first kernel to a streaming input port of the second kernel. Valid values
include:
<cu_name>.<streaming_output_port>:<cu_name>.<streaming_input_port>[:<fifo_depth>]
Where:
-
<cu_name>
is the compute unit name specified in the--connectivity.nk
option. Generally this is<kernel_name>_1
unless a different name was specified. -
<streaming_output_port>/<streaming_input_port>
is the function argument for the compute unit port that is declared as an AXI4-Stream. -
[:<fifo_depth>]
inserts a FIFO of the specified depth between the two streaming ports to prevent stalls. The value is specified as an integer.
--connectivity.sc
kernel drives
itself.For example, to connect the AXI4-Stream port s_out
of the
compute unit mem_read_1
to AXI4-Stream port s_in
of the compute unit increment_1
, use the following:
--connectivity.sc mem_read_1.s_out:increment_1.s_in
[connectivity]
section head using the following
format:[connectivity]
sc=mem_read_1.s_out:increment_1.s_in
The inclusion of the optional <fifo_depth> value lets the
v++
linker add a FIFO between the two kernels
to help prevent stalls. This uses BRAM resources from the device when specified, but
eliminates the need to update the HLS kernel to contain FIFOs. The tool also
instantiates a Clock Converter (CDC) or Datawidth Converter (DWC) IP if the
connections have different clocks, or different bus widths.
--connectivity.slr
--connectivity.slr <arg>
Use this option to assign a CU to a specific SLR on the device. The option must be repeated for each kernel or CU being assigned to an SLR.
--connectivity.slr
to assign the kernel placement, then you must also
use --connectivity.sp
to assign memory access for
the kernel.Valid values include:
<cu_name>:<SLR_NUM>
Where:
-
<cu_name>
is the name of the compute unit as specified in the--connectivity.nk
option. Generally this is<kernel_name>_1
unless a different name was specified. -
<SLR_NUM>
is the SLR number to assign the CU to. For example, SLR0, SLR1.
For example, to assign CU vadd_2
to SLR2, and CU fft_1
to SLR1, use the
following:
v++ --link --connectivity.slr vadd_2:SLR2 --connectivity.slr fft_1:SLR1
[connectivity]
section head using the following
format:[connectivity]
slr=vadd_2:SLR2
slr=fft_1:SLR1
--connectivity.sp
--connectivity.sp <arg>
Use this option to specify the assignment of kernel arguments to
system ports within the platform. A primary use case for this option is to connect
kernel arguments to specific memory resources. A separate --connectivity.sp
option is required to map each argument of a kernel
to a particular memory resource. Any argument not explicitly mapped to a memory
resource through the --connectivity.sp
option is
automatically connected to an available memory resource during the build
process.
--connectivity.sp
option as
this provides the greatest connection flexibility. However, you can also specify
kernel interface ports with this option. Valid values include:
<cu_name>.<kernel_argument_name>:<sptag[min:max]>
Where:
-
<cu_name>
is the name of the compute unit as specified in the--connectivity.nk
option. Generally this is<kernel_name>_1
unless a different name was specified. -
<kernel_argument_name>
is the name of the function argument for the kernel, or the compute unit interface port. -
<sptag>
represents a system port tag, such as for memory controller interface names from the target platform. Valid<sptag>
names include DDR, PLRAM, and HBM. -
[min:max]
enables the use of a range of memory, such as DDR[0:2]. A single index is also supported: DDR[2].
<sptag>
and range of memory resources for a target platform can
be obtained using the platforminfo
command. Refer
to platforminfo Utility for more information.The following example maps the input argument (A) for the specified CU of the VADD kernel to DDR[0:3], input argument (B) to HBM[0:31], and writes the output argument (C) to PLRAM[2]:
v++ --link --connectivity.sp vadd_1.A:DDR[0:3] --connectivity.sp vadd_1.B:HBM[0:31] \
--connectivity.sp vadd_1.C:PLRAM[2]
[connectivity]
section head using the following
format:[connectivity]
sp=vadd_1.A:DDR[0:3]
sp=vadd_1.B:HBM[0:31]
sp=vadd_1.C:PLRAM[2]
--connectivity.noc.connect
--connectivity.noc.connect <arg>
Where <arg>
is in the form
of <compute_unit_name>.<kernel_interface_name>:<noc
interface>
, and specifies a connection between the PL kernel
interface and the Versal NoC. Valid values are
internal memory controllers, or master interfaces on the Versal NoC cell.
The Vitis compiler estimates kernel bandwidth requirements based on NoC connectivity and M_AXI properties (datawidth * clock freq) across the dynamic region, and automatically sets NoC configuration settings for read and write bandwidth, scaling as needed to avoid exceeding the available bandwidth.
[connectivity]
noc.read_bw=mm2s.M_AXI:2000.16
noc.write_bw=mm2s.M_AXI:2010.16
noc.connect=mm2s.M_AXI:M00_INI
--connectivity.noc.read_bw
--connectivity.noc.read_bw <arg>
Where <arg>
is in the form
<compute_unit_name>.<kernel_interface_name>:<Bandwidth>.<Avg_burst_length>
,
and specifies both the bandwidth and burst length of the connection. The bandwidth
is specified in MB/s.
This option specifies expected read traffic characteristics on M_AXI interfaces to let you override the automatic Versal NoC configuration.
--connectivity.noc.write_bw
--connectivity.noc.write_bw <arg>
Where <arg> is in the form <compute_unit_name>.<kernel_interface_name>:<Bandwidth>.<Avg_burst_length>
,
and specifies both the bandwidth and burst length of the connection. The bandwidth
is specified in MB/s.
This option specifies expected write traffic characteristics on M_AXI interfaces to let you override the automatic Versal NoC configuration.
--connectivity.connect
--connectivity.connect <X:Y>
This option can be used to make connections through the Vivado IP integrator, but v++
does not perform any error checking on the specified connections.
Use this to specify general connections between kernels and non-AXI elements of the
target platform, such as connections to GT ports.
connect_bd_net
or
connect_bd_intf_net
commands. The specific
format of <X:Y>
is:
src/hierarchy_name/cell_name/pin_name:dst/hierarchy_name/cell_name/pin_name
These cannot include connections between AXI4-Stream interfaces which require the use of --conectivity.sc
, or M_AXI interfaces which require
the use of --connectivity.sp
as described
above.
[connectivity]
section head using the following
format:[connectivity]
connect=<X:Y>