Intel® High Level Synthesis Compiler Pro Edition: Reference Manual

ID 683349
Date 6/20/2022

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4.4. Avalon® Memory-Mapped Host Interfaces

A component can interface with an external memory over an Avalon® Memory-Mapped (MM) Host interface.
You can specify the Avalon® MM Host interface implicitly using a function pointer argument or reference argument, or explicitly using the mm_host<> class defined in the "HLS/hls.h" header file. Describe a customized Avalon® MM Host interface in your code by including a reference to an mm_host<> object in your component function signature.

Each mm_host argument of a component results in an input conduit for the address. That input conduit is associated with the component start and busy signals. In addition to this input conduit, a unique Avalon® MM Host interface is created for each address space. Host interfaces that share the same address space are arbitrated on the same interface.

Avalon® MM Host interfaces on components always issue requests that address only bytes (not words). For example, the following code example results in 0x0018 on the mm_host interface because 0x0018 = 0x0006 << 2.
// 32-bit wide word

ihc::mm_master<uint32_t, ihc::dwidth<32>, ihc::awidth<16>, ihc::latency<0>, ihc::waitrequest<true>, ihc::aspace<1>> mm_a;
uint32_t value = mm_a[0x0006];
In contrast, the following code example results in 0x0006 on the mm_host interface because 0x0006 = 0x0006 << 2.
// 8-bit wide word

ihc::mm_master<uint8_t, ihc::dwidth<32>, ihc::awidth<16>, ihc::latency<0>, ihc::waitrequest<true>, ihc::aspace<2>> mm_b;
uint32_t value = mm_a[0x0006];

For more information about Avalon® MM Host interfaces, refer to "Avalon Memory-Mapped Interfaces" in Avalon Interface Specifications.

Table 13.   Intel® HLS Compiler Pro Edition Memory-Mapped Interfaces Summary
Template Object or Parameter Description
ihc::mm_host The underlying pointer type.
ihc::dwidth The width of the memory-mapped data bus in bits
ihc::awidth The width of the memory-mapped address bus in bits.
ihc::aspace The address space of the interface that associates with the host.
ihc::latency The guaranteed latency from when a read command exits the component when the external memory returns valid read data.
ihc::maxburst The maximum number of data transfers that can associate with a read or write transaction.
ihc::align The alignment of the base pointer address in bytes.
ihc::readwrite_mode The port direction of the interface.

Adds the waitrequest signal that is asserted by the agent when it is unable to respond to a read or write request.

getInterfaceAtIndex This testbench function is used to index into an mm_host object.