Native Loopback Accelerator Functional Unit (AFU) User Guide

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UG-20092 | 2018.08.06

About this Document

Conventions

Table 1. Document Conventions
Convention	Description
#	Precedes a command that indicates the command is to be entered as root.
$	Indicates a command is to be entered as a user.
`This font`	Filenames, commands, and keywords are printed in this font. Long command lines are printed in this font. Although long command lines may wrap to the next line, the return is not part of the command; do not press enter.
`<variable_name>`	Indicates the placeholder text that appears between the angle brackets must be replaced with an appropriate value. Do not enter the angle brackets.

Acronyms

Table 2. Acronyms
Acronyms	Expansion	Description
AF	Accelerator Function	Compiled Hardware Accelerator image implemented in FPGA logic that accelerates an application.
AFU	Accelerator Functional Unit	Hardware Accelerator implemented in FPGA logic which offloads a computational operation for an application from the CPU to improve performance.
API	Application Programming Interface	A set of subroutine definitions, protocols, and tools for building software applications.
ASE	AFU Simulation Environment	Co-simulation environment that allows you to use the same host application and AF in a simulation environment. ASE is part of the Intel^® Acceleration Stack for FPGAs.
CCI-P	Core Cache Interface	CCI-P is the standard interface AFUs use to communicate with the host.
CL	Cache Line	64-byte cache line
DFH	Device Feature Header	Creates a linked list of feature headers to provide an extensible way of adding features.
FIM	FPGA Interface Manager	The FPGA hardware containing the FPGA Interface Unit (FIU) and external interfaces for memory, networking, etc. The Accelerator Function (AF) interfaces with the FIM at run time.
FIU	FPGA Interface Unit	FIU is a platform interface layer that acts as a bridge between platform interfaces like PCIe^® , UPI and AFU-side interfaces such as CCI-P.
MPF	Memory Properties Factory	The MPF is a Basic Building Block (BBB) that AFUs can use to provide CCI-P traffic shaping operations for transactions with the FIU.
Msg	Message	Message - a control notification
NLB	Native Loopback	The NLB performs reads and writes to the CCI-P link to test connectivity and throughput.
RdLine_I	Read Line Invalid	Memory Read Request, with FPGA cache hint set to invalid. The line is not cached in the FPGA, but may cause FPGA cache pollution. Note: The cache tag tracks the request status for all outstanding requests on Intel^® Ultra Path Interconnect ( Intel^® UPI). Therefore, even though RdLine_I is marked invalid upon completion, it consumes the cache tag temporarily to track the request status over UPI. This action may result in the eviction of a cache line, resulting in cache pollution. The advantage of using RdLine_I is that it is not tracked by CPU directory; thus it prevents snooping from CPU.
RdLine-S	Read Line Shared	Memory read request with FPGA cache hint set to shared. An attempt is made to keep it in the FPGA cache in a shared state.
WrLine_I	Write Line Invalid	Memory Write Request, with FPGA cache hint set to Invalid. The FIU writes the data with no intention of keeping the data in FPGA cache.
WrLine_M	Write Line Modified	Memory Write Request, with the FPGA cache hint set to Modified. The FIU writes the data and leaves it in the FPGA cache in a modified state.

Acceleration Glossary

Table 3. Acceleration Stack for Intel^® Xeon^® CPU with FPGAs Glossary
Term	Abbreviation	Description
Intel^® Acceleration Stack for Intel^® Xeon^® CPU with FPGAs	Acceleration Stack	A collection of software, firmware, and tools that provides performance-optimized connectivity between an Intel^® FPGA and an Intel^® Xeon^® processor.
Intel^® Programmable Acceleration Card with Intel^® Arria^® 10 GX FPGA	Intel^® PAC with Intel^® Arria^® 10 GX FPGA	PCIe^® accelerator card with an Intel^® Arria^® 10 FPGA. Programmable Acceleration Card is abbreviated PAC. Contains a FPGA Interface Manager (FIM) that connects to an Intel^® Xeon^® processor over PCIe^® bus.
Intel^® Xeon^® Scalable Platform with Integrated FPGA	Integrated FPGA Platform	A platform with the Intel^® Xeon^® and FPGA in a single package and sharing a coherent view of memory using the Intel Ultra Path Interconnect (UPI).

The Native Loopback Accelerator Functional Unit (AFU)

Native Loopback (NLB) AFU Overview

The NLB sample AFUs comprise a set of Verilog and System Verilog files to test memory reads and writes, bandwidth, and latency.

This package includes three AFUs that you can build from the same RTL source. Your configuration of the RTL source code creates these AFUs.

The NLB Sample Accelerator Function (AF)

The $OPAE_PLATFORM_ROOT/hw/samples directory stores source code for the following NLB sample AFUs:

nlb_mode_0
nlb_mode_0_stp
nlb_mode_3

Note: The $DCP_LOC/hw/samples directory stores the NLB sample AFUs source code for the 1.0 Production release package.

To understand the NLB sample AFU source code structure and how to build it, refer to the Intel^® Acceleration Stack Quick Start Guide for Intel^® Programmable Acceleration Card with Intel^® Arria^® 10 GX FPGA .

The release package provides the following three sample AFs:

NLB mode 0 AF: requires hello_fpga or fpgadiag utility to perform the lpbk1 test.
NLB mode 3 AF: requires fpgadiag utility to perform the trupt, read, and write tests.
NLB mode 0 stp AF: requires hello_fpga or fpgadiag utility to perform the lpbak1 test.
Note: The nlb_mode_0_stp is the same AFU as nlb_mode_0 but with Signal Tap debug feature enabled.

The fpgadiag and hello_fpga utilities help the appropriate AF to diagnose, test and report on the FPGA hardware.

Figure 1. Native Loopback (nlb_lpbk.sv) Top Level Wrapper

The following files implement the loopback function shown in the figure above:

Table 4. NLB Files
File Name	Description
nlb_lpbk.sv	Top-level wrapper for NLB that instantiates the requestor and arbiter.
arbiter.sv	Instantiates the test AF.
requestor.sv	Accepts requests from the arbiter and formats the requests according to the CCI-P specification. Also implements flow control.
nlb_csr.sv	Implements a 64-bit read/write `Control and Status (CSR)` registers. The registers support both 32- and 64-bit reads and writes.
nlb_gram_sdp.sv	Implements a generic dual-port RAM with one write port and one read port.

NLB is a reference implementation of an AFU compatible with the Intel^® Acceleration Stack for Intel^® Xeon^® CPU with FPGAs Core Cache Interface (CCI-P) Reference Manual. NLB’s primary function is to validate host connectivity using different memory access patterns. NLB also measures bandwidth and read/write latency. The bandwidth test has the following options:

100% read
100% write
50% read and 50% writes

Native Loopback Control and Status Register Descriptions

Table 5. CSR Names, Addresses and Descriptions
Byte Address (OPAE)	Word Address (CCI-P)	Access	Name	Width	Description
0x0000	0x0000	RO	`DFH`	64	AF Device Feature Header.
0x0008	0x0002	RO	`AFU_ID_L`	64	AF ID low.
0x0010	0x0004	RO	`AFU_ID_H`	64	AF ID high.
0x0018	0x0006	Rsvd	`CSR_DFH_RSVD0`	64	Mandatory Reserved 0.
0x0020	0x0008	RO	`CSR_DFH_RSVD1`	64	Mandatory Reserved 1.
0x0100	0x0040	RW	`CSR_SCRATCHPAD0`	64	Scratchpad register 0.
0x0108	0x0042	RW	`CSR_SCRATCHPAD1`	64	Scratchpad register 2.
0x0110	0x0044	RW	`CSR_AFU_DSM_BASEL`	32	Lower 32-bits of AF DSM base address. The lower 6 bits are 4x00 because the address is aligned to the 64-byte cache line size.
0x0114	0x0045	RW	`CSR_AFU_DSM_BASEH`	32	Upper 32-bits of AF DSM base address.
0x0120	0x0048	RW	`CSR_SRC_ADDR`	64	Start physical address for source buffer. All read requests target this region.
0x0128	0x004A	RW	`CSR_DST_ADDR`	64	Start physical address for destination buffer. All write requests target this region
0x0130	0x004C	RW	`CSR_NUM_LINES`	32	Number of cache lines.
0x0138	0x004E	RW	`CSR_CTL`	32	Controls test flow, start, stop, force completion.
0x0140	0x0050	RW	`CSR_CFG`	32	Configures test parameters.
0x0148	0x0052	RW	`CSR_INACT_THRESH`	32	Inactivity threshold limit.
0x0150	0x0054	RW	`CSR_INTERRUPT0`	32	SW allocates Interrupt APIC ID and Vector to device.
DSM Offset Map
0x0040	0x0010	RO	`DSM_STATUS`	32	Test status and error register.

Table 6. CSR Bit Fields with Examples. This table lists the CSR bit fields that depend on the value of the `CSR_NUM_LINES`, `<N>`. In the example below `<N>` = 14.
Name	Bit Field	Access	Description
`CSR_SRC_ADDR`	[63:`<N>`]	RW	2^(N+6)MB aligned address points to the start of the read buffer.
`CSR_SRC_ADDR`	[`<N>`-1:0]	RW	0x0.
`CSR_DST_ADDR`	[63:`<N>`]	RW	2^(N+6)MB aligned address points to the start of the write buffer.
`CSR_DST_ADDR`	[`<N>`-1:0]	RW	0x0.
`CSR_NUM_LINES`	[31:`<N>`]	RW	0x0.
`CSR_NUM_LINES`	[`<N>`-1:0]	RW	Number of cache lines to read or write. This threshold may be different for each test AF. Note: Ensure that source and destination buffers are large enough to accommodate the `<N>` cache lines. `CSR_NUM_LINES` should be less than or equal to `<N>`.
For the following values, assume `<N>`=14. Then, `CSR_SRC_ADDR` and `CSR_DST_ADDR` accept 2^20 (0x100000).
`CSR_SRC_ADDR`	[31:14]	RW	1MB aligned address.
`CSR_SRC_ADDR`	[13:0]	RW	0x0.
`CSR_DST_ADDR`	[31:14]	RW	1MB aligned address.
`CSR_DST_ADDR`	[13:0]	RW	0x0.
`CSR_NUM_LINES`	[31:14]	RW	0x0.
`CSR_NUM_LINES`	[13:0]	RW	Number of cache lines to read or write. This threshold may be different for each test AF. Note: Ensure that source and destination buffers are large enough to accommodate the `<N>` cache lines.

Table 7. Additional CSR Bit Fields
Name	Bit Field	Access	Description
`CSR_CTL`	[31:3]	RW	Reserved.
	[2]	RW	Force test completion. Writes test completion flag and other performance counters to `csr_stat`. After forcing test completion, the hardware state is identical to a non-forced test completion.
	[1]	RW	Starts test execution.
	[0]	RW	Active low test reset. When low, all configuration parameters change to their default values.
`CSR_CFG`	[29]	RW	`cr_interrupt_testmode` tests interrupts. Generates an interrupt at the end of each test.
	[28]	RW	`cr_interrupt_on_error` sends an interrupt when upon error detection.
	[27:20]	RW	`cr_test_cfg` configures the behavior of each test mode.
	[13:12]	RW	`cr_chsel` selects the virtual channel.
	[10:9]	RW	`cr_rdsel` configures the read request type. The encodings have the following valid values: 1'b00: `RdLine_S` 2'b01: `RdLine_I` 2'b11: `Mixed mode`
	[8]	RW	`cr_delay_en` enables random delay insertion between requests.
	[6:5]	RW	Configures test mode,`cr_multiCL-len`. Valid values are 0,1,and 3.
	[4:2]	RW	`cr_mode`, configures test mode. The following values are valid: 3'b000: LPBK1 3'b001: Read 3'b010: Write 3'b011: TRPUT For more information about the test mode, refer to the Test Modes topic below.
	[1]	RW	`c_cont` selects test rollover or test termination. When 1'b0, the test terminates. Updates the status CSR when`CSR_NUM_LINES` count is reached. When 1'b1, the test rolls over to the start address after it reaches the `CSR_NUM_LINES` count. In rollover mode, the test terminates only upon error.
	[0]	RW	`cr_wrthru_en` switches between `WrLine_I` and `Wrline_M` request types. 1'b0: `WrLine_M` 1'b1: `WrLine_I`
`CSR_INACT_THRESHOLD`	[31:0]	RW	Inactivity threshold limit. Detects the duration of stalls during a test run. Counts the number of consecutive idle cycles. If the `inactivity count > CSR_INACT_THRESHOLD`, no requests are sent, no responses are received, and the `inact_timeout` signal is set. Writing 1 to `CSR_CTL[1]` activates this counter.
`CSR_INTERRUPT0`	[23:16]	RW	The Interrupt Vector Number for the device.
`CSR_INTERRUPT0`	[15:0]	RW	`apic_id` is the APIC OD for the device.
`DSM_STATUS`	[511:256]	RO	Error dump form Test Mode.
	[255:224]	RO	End Overhead.
	[223:192]	RO	Start Overhead.
	[191:160]	RO	Number of Writes.
	[159:128]	RO	Number of Reads.
	[127:64]	RO	Number of Clocks.
	[63:32]	RO	Test error register.
	[31:16]	RO	Compare and exchange success counter.
	[15:1]	RO	Unique ID for each DSM status write.
	[0]	RO	Test completion flag.

Test Modes

CSR_CFG[4:2] configures the test mode. The following four tests are available:

LPBK1: This is a memory copy test. The AF copies CSR_NUM_LINES from the source buffer to the destination buffer. Upon test completion, the software compares the source and destination buffers.
Read: This test stresses the read path and measures read bandwidth or latency. The AF reads CSR_NUM_LINES starting from the CSR_SRC_ADDR. This is only a bandwidth or latency test. It does not verify the data read.
Write: This test stresses the write path and measures write bandwidth or latency. The AF reads CSR_NUM_LINES starting from the CSR_SRC_ADDR. This is only a bandwidth or latency test. It does not verify the data written.
TRPUT: This test combines the reads and writes. It reads CSR_NUM_LINES starting from CSR_SRC_ADDR location and writes CSR_NUM_LINES to CSR_SRC_ADDR. It also measures read and write bandwidth. This test does not check the data. The reads and writes have no dependencies

The following table shows the CSR_CFG encodings for the four tests. This table sets and CSR_NUM_LINES, <N>=14. You can change the number of cache lines by updating the CSR_NUM_LINES register.

Table 8. Test Modes
Test Mode	Encoding CSR_CFG[4:2]	Cache Line Threshold CSR_NUM_LINES	Cache Line Threshold for `<N>`=14
LPBK1	3'b000	2^<N>	14'h3FFF
Read	3'b001	2^<N>	14'h3FFF
Write	3'b010	2^<N>	14'h3FFF
TRPUT	3'b011	2^<N>	14'h3FFF

FPGA Diagnostics: fpgadiag

The fpgadiag utililty includes several tests to diagnose, test, and report on the FPGA hardware. Use the fpgadiag utility to run all the test modes. For more information about using the fpgadiag utility, refer to the fpgadiag section in the OPAE FPGA Tools Guide.

NLB Mode0 Hello_FPGA Test Flow

Software initializes Device Status Memory (DSM) to zero.
Software writes the DSM BASE address to the AFU.
CSR Write(DSM_BASE_H), CSRWrite(DSM_BASE_L)
Software prepares source and destination memory buffer. This preparation is test specific.
Software writes CSR_CTL[2:0]= 0x1. This write brings the test out of reset and into configuration mode. Configuration can proceed only when CSR_CTL[0]=1 & CSR_CTL[1]=1.
Software configures the test parameters, such as src, destaddress, csr_cfg, num lines, and so on.
Software CSR writes CSR_CTL[2:0]= 0x3. The AF begins test execution.
Test completion:
- Hardware completes when the test completes or detects an error. Upon completion, the hardware AF updates DSM_STATUS. Software polls DSM_STATUS[31:0]==1 to detect test completion.
- Software can force test completion by writing CSR writes CSR_CTL[2:0]=0x7. Hardware AF updates DSM_STATUS.

Document Revision History for the Native Loopback Accelerator Functional Unit (AFU) User Guide

Document Version	Intel^® Acceleration Stack Version	Changes
2018.08.06	1.1 Production (supported with Intel^® Quartus^® Prime Pro Edition 17.1.1) and 1.0 Production (supported with Intel^® Quartus^® Prime Pro Edition 17.0.0)	Updated the location of the source code for the NLB sample AFU in The NLB Sample Accelerator Function (AF) section.
2018.04.11	1.0 Production (supported with Intel^® Quartus^® Prime Pro Edition 17.0.0)	Added new `nlb_mode_0_stp` NLB sample AFU. Updated the location of the source code for the NLB sample AFU in The NLB Sample Accelerator Function (AF) section.
2017.12.22	1.0 Beta (supported with Intel^® Quartus^® Prime Pro Edition 17.0.0)	Initial release.