7. Intel® ACC200 vRAN Dedicated Accelerator Poll Mode Driver

The Intel® vRAN Dedicated Accelerator ACC200 peripheral enables cost-effective 4G and 5G next-generation virtualized Radio Access Network (vRAN) solutions integrated on Sapphire Rapids Edge Enhanced Processor (SPR-EE) Intel® 7 based Xeon® multi-core server processor.

7.1. Features

The ACC200 includes a 5G Low Density Parity Check (LDPC) encoder/decoder, rate match/dematch, Hybrid Automatic Repeat Request (HARQ) with access to DDR memory for buffer management, a 4G Turbo encoder/decoder, a Fast Fourier Transform (FFT) block providing DFT/iDFT processing offload for the 5G Sounding Reference Signal (SRS), a Queue Manager (QMGR), and a DMA subsystem. There is no dedicated on-card memory for HARQ, this is using coherent memory on the CPU side.

These correspond to the following features exposed by the PMD:

  • LDPC Encode in the Downlink (5GNR)
  • LDPC Decode in the Uplink (5GNR)
  • Turbo Encode in the Downlink (4G)
  • Turbo Decode in the Uplink (4G)
  • FFT processing
  • SR-IOV with 16 VFs per PF
  • Maximum of 256 queues per VF
  • MSI

ACC200 PMD supports the following bbdev capabilities:

  • For the LDPC encode operation:
    • RTE_BBDEV_LDPC_CRC_24B_ATTACH: set to attach CRC24B to CB(s).
    • RTE_BBDEV_LDPC_RATE_MATCH: if set then do not do Rate Match bypass.
    • RTE_BBDEV_LDPC_INTERLEAVER_BYPASS: if set then bypass interleaver.
  • For the LDPC decode operation:
    • RTE_BBDEV_LDPC_CRC_TYPE_24B_CHECK: check CRC24B from CB(s).
    • RTE_BBDEV_LDPC_CRC_TYPE_24B_DROP: drops CRC24B bits appended while decoding.
    • RTE_BBDEV_LDPC_CRC_TYPE_24A_CHECK: check CRC24A from CB(s).
    • RTE_BBDEV_LDPC_CRC_TYPE_16_CHECK: check CRC16 from CB(s).
    • RTE_BBDEV_LDPC_HQ_COMBINE_IN_ENABLE: provides an input for HARQ combining.
    • RTE_BBDEV_LDPC_HQ_COMBINE_OUT_ENABLE: provides an input for HARQ combining.
    • RTE_BBDEV_LDPC_ITERATION_STOP_ENABLE: disable early termination.
    • RTE_BBDEV_LDPC_DEC_SCATTER_GATHER: supports scatter-gather for input/output data.
    • RTE_BBDEV_LDPC_HARQ_6BIT_COMPRESSION: supports compression of the HARQ input/output.
    • RTE_BBDEV_LDPC_LLR_COMPRESSION: supports LLR input compression.
  • For the turbo encode operation:
    • RTE_BBDEV_TURBO_CRC_24B_ATTACH: set to attach CRC24B to CB(s).
    • RTE_BBDEV_TURBO_RATE_MATCH: if set then do not do Rate Match bypass.
    • RTE_BBDEV_TURBO_ENC_INTERRUPTS: set for encoder dequeue interrupts.
    • RTE_BBDEV_TURBO_RV_INDEX_BYPASS: set to bypass RV index.
    • RTE_BBDEV_TURBO_ENC_SCATTER_GATHER: supports scatter-gather for input/output data.
  • For the turbo decode operation:
    • RTE_BBDEV_TURBO_CRC_TYPE_24B: check CRC24B from CB(s).
    • RTE_BBDEV_TURBO_SUBBLOCK_DEINTERLEAVE: perform subblock de-interleave.
    • RTE_BBDEV_TURBO_DEC_INTERRUPTS: set for decoder dequeue interrupts.
    • RTE_BBDEV_TURBO_NEG_LLR_1_BIT_IN: set if negative LLR input is supported.
    • RTE_BBDEV_TURBO_DEC_TB_CRC_24B_KEEP: keep CRC24B bits appended while decoding.
    • RTE_BBDEV_TURBO_DEC_CRC_24B_DROP: option to drop the code block CRC after decoding.
    • RTE_BBDEV_TURBO_EARLY_TERMINATION: set early termination feature.
    • RTE_BBDEV_TURBO_DEC_SCATTER_GATHER: supports scatter-gather for input/output data.
    • RTE_BBDEV_TURBO_HALF_ITERATION_EVEN: set half iteration granularity.
    • RTE_BBDEV_TURBO_SOFT_OUTPUT: set the APP LLR soft output.
    • RTE_BBDEV_TURBO_EQUALIZER: set the turbo equalizer feature.
    • RTE_BBDEV_TURBO_SOFT_OUT_SATURATE: set the soft output saturation.
    • RTE_BBDEV_TURBO_CONTINUE_CRC_MATCH: set to run an extra odd iteration after CRC match.
    • RTE_BBDEV_TURBO_NEG_LLR_1_BIT_SOFT_OUT: set if negative APP LLR output supported.
    • RTE_BBDEV_TURBO_MAP_DEC: supports flexible parallel MAP engine decoding.
  • For the FFT operation:
    • RTE_BBDEV_FFT_WINDOWING: flexible windowing capability.
    • RTE_BBDEV_FFT_CS_ADJUSTMENT: flexible adjustment of Cyclic Shift time offset.
    • RTE_BBDEV_FFT_DFT_BYPASS: set for bypass the DFT and get directly into iDFT input.
    • RTE_BBDEV_FFT_IDFT_BYPASS: set for bypass the IDFT and get directly the DFT output.
    • RTE_BBDEV_FFT_WINDOWING_BYPASS: set for bypass time domain windowing.

7.2. Installation

Section 3 of the DPDK manual provides instructions on installing and compiling DPDK.

DPDK requires hugepages to be configured as detailed in section 2 of the DPDK manual. The bbdev test application has been tested with a configuration 40 x 1GB hugepages. The hugepage configuration of a server may be examined using:

grep Huge* /proc/meminfo

7.3. Initialization

When the device first powers up, its PCI Physical Functions (PF) can be listed through these commands for ACC200:

sudo lspci -vd8086:57c0

The physical and virtual functions are compatible with Linux UIO drivers: vfio and igb_uio. However, in order to work the 5G/4G FEC device first needs to be bound to one of these Linux drivers through DPDK.

7.3.1. Bind PF UIO driver(s)

Install the DPDK igb_uio driver, bind it with the PF PCI device ID and use lspci to confirm the PF device is under use by igb_uio DPDK UIO driver.

The igb_uio driver may be bound to the PF PCI device using one of two methods for ACC200:

#. PCI functions (physical or virtual, depending on the use case) can be bound to the UIO driver by repeating this command for every function.

cd <dpdk-top-level-directory>
insmod build/kmod/igb_uio.ko
echo "8086 57c0" > /sys/bus/pci/drivers/igb_uio/new_id
lspci -vd8086:57c0
  1. Another way to bind PF with DPDK UIO driver is by using the dpdk-devbind.py tool
cd <dpdk-top-level-directory>
usertools/dpdk-devbind.py -b igb_uio 0000:f7:00.0

where the PCI device ID (example: 0000:f7:00.0) is obtained using lspci -vd8086:57c0.

In a similar way the PF may be bound with vfio-pci as any PCIe device.

7.3.2. Enable Virtual Functions

Now, it should be visible in the printouts that PCI PF is under igb_uio control “Kernel driver in use: igb_uio

To show the number of available VFs on the device, read sriov_totalvfs file.

cat /sys/bus/pci/devices/0000\:<b>\:<d>.<f>/sriov_totalvfs

where 0000\:<b>\:<d>.<f> is the PCI device ID

To enable VFs via igb_uio, echo the number of virtual functions intended to enable to max_vfs file.

echo <num-of-vfs> > /sys/bus/pci/devices/0000\:<b>\:<d>.<f>/max_vfs

Afterwards, all VFs must be bound to appropriate UIO drivers as required, same way it was done with the physical function previously.

Enabling SR-IOV via VFIO driver is pretty much the same, except that the file name is different:

echo <num-of-vfs> > /sys/bus/pci/devices/0000\:<b>\:<d>.<f>/sriov_numvfs

7.3.3. Configure the VFs through PF

The PCI virtual functions must be configured before working or getting assigned to VMs/Containers. The configuration involves allocating the number of hardware queues, priorities, load balance, bandwidth and other settings necessary for the device to perform FEC functions.

This configuration needs to be executed at least once after reboot or PCI FLR and can be achieved by using the functions rte_acc200_configure(), which sets up the parameters defined in the compatible acc200_conf structure.

7.4. Test Application

The bbdev class is provided with a test application, test-bbdev.py and range of test data for testing the functionality of the device, depending on the device’s capabilities. The test application is located under app/test-bbdev folder and has the following options:

"-p", "--testapp-path": specifies path to the bbdev test app.
"-e", "--eal-params": EAL arguments which are passed to the test app.
"-t", "--timeout": Timeout in seconds (default=300).
"-c", "--test-cases": Defines test cases to run. Run all if not specified.
"-v", "--test-vector": Test vector path.
"-n", "--num-ops": Number of operations to process on device (default=32).
"-b", "--burst-size": Operations enqueue/dequeue burst size (default=32).
"-s", "--snr": SNR in dB used when generating LLRs for bler tests.
"-s", "--iter_max": Number of iterations for LDPC decoder.
"-l", "--num-lcores": Number of lcores to run (default=16).
"-i", "--init-device": Initialise PF device with default values.

To execute the test application tool using simple decode or encode data, type one of the following:

./test-bbdev.py -c validation -n 64 -b 1 -v ./ldpc_dec_default.data
./test-bbdev.py -c validation -n 64 -b 1 -v ./ldpc_enc_default.data

The test application test-bbdev.py, supports the ability to configure the PF device with a default set of values, if the “-i” or “- -init-device” option is included. The default values are defined in test_bbdev_perf.c.

7.4.1. Test Vectors

In addition to the simple LDPC decoder and LDPC encoder tests, bbdev also provides a range of additional tests under the test_vectors folder, which may be useful. The results of these tests will depend on the device capabilities which may cause some test cases to be skipped, but no failure should be reported.

7.4.2. Alternate Baseband Device configuration tool

On top of the embedded configuration feature supported in test-bbdev using “- -init-device” option mentioned above, there is also a tool available to perform that device configuration using a companion application. The pf_bb_config application notably enables then to run bbdev-test from the VF and not only limited to the PF as captured above.

See for more details: https://github.com/intel/pf-bb-config

Specifically for the bbdev ACC200 PMD, the command below can be used:

pf_bb_config ACC200 -c ./acc200/acc200_config_vf_5g.cfg
test-bbdev.py -e="-c 0xff0 -a${VF_PCI_ADDR}" -c validation -n 64 -b 64 -l 1 -v ./ldpc_dec_default.data