16. Wireless Baseband Device Library
The Wireless Baseband library provides a common programming framework that abstracts HW accelerators based on FPGA and/or Fixed Function Accelerators that assist with 3GPP Physical Layer processing. Furthermore, it decouples the application from the compute-intensive wireless functions by abstracting their optimized libraries to appear as virtual bbdev devices.
The functional scope of the BBDEV library are those functions in relation to the 3GPP Layer 1 signal processing (channel coding, modulation, …).
The framework currently only supports FEC function.
16.1. Design Principles
The Wireless Baseband library follows the same ideology of DPDK’s Ethernet Device and Crypto Device frameworks. Wireless Baseband provides a generic acceleration abstraction framework which supports both physical (hardware) and virtual (software) wireless acceleration functions.
16.2. Device Management
16.2.1. Device Creation
Physical bbdev devices are discovered during the PCI probe/enumeration of the EAL function which is executed at DPDK initialization, based on their PCI device identifier, each unique PCI BDF (bus/bridge, device, function).
Virtual devices can be created by two mechanisms, either using the EAL command line options or from within the application using an EAL API directly.
From the command line using the –vdev EAL option
--vdev 'baseband_turbo_sw,max_nb_queues=8,socket_id=0'
Or using the rte_vdev_init API within the application code.
rte_vdev_init("baseband_turbo_sw", "max_nb_queues=2,socket_id=0")
All virtual bbdev devices support the following initialization parameters:
max_nb_queues- maximum number of queues supported by the device.socket_id- socket on which to allocate the device resources on.
16.2.2. Device Identification
Each device, whether virtual or physical is uniquely designated by two identifiers:
A unique device index used to designate the bbdev device in all functions exported by the bbdev API.
A device name used to designate the bbdev device in console messages, for administration or debugging purposes. For ease of use, the port name includes the port index.
16.2.3. Device Configuration
From the application point of view, each instance of a bbdev device consists of one or more queues identified by queue IDs. While different devices may have different capabilities (e.g. support different operation types), all queues on a device support identical configuration possibilities. A queue is configured for only one type of operation and is configured at initialization time. When an operation is enqueued to a specific queue ID, the result is dequeued from the same queue ID.
Configuration of a device has two different levels: configuration that applies to the whole device, and configuration that applies to a single queue.
Device configuration is applied with
rte_bbdev_setup_queues(dev_id,num_queues,socket_id)
and queue configuration is applied with
rte_bbdev_queue_configure(dev_id,queue_id,conf). Note that, although all
queues on a device support same capabilities, they can be configured differently
and will then behave differently.
Devices supporting interrupts can enable them by using
rte_bbdev_intr_enable(dev_id).
The configuration of each bbdev device includes the following operations:
Allocation of resources, including hardware resources if a physical device.
Resetting the device into a well-known default state.
Initialization of statistics counters.
The rte_bbdev_setup_queues API is used to setup queues for a bbdev device.
int rte_bbdev_setup_queues(uint16_t dev_id, uint16_t num_queues,
int socket_id);
num_queuesargument identifies the total number of queues to setup for this device.socket_idspecifies which socket will be used to allocate the memory.
The rte_bbdev_intr_enable API is used to enable interrupts for a bbdev
device, if supported by the driver. Should be called before starting the device.
int rte_bbdev_intr_enable(uint16_t dev_id);
16.2.4. Queues Configuration
Each bbdev devices queue is individually configured through the
rte_bbdev_queue_configure() API.
Each queue resources may be allocated on a specified socket.
struct rte_bbdev_queue_conf {
int socket;
uint32_t queue_size;
uint8_t priority;
bool deferred_start;
enum rte_bbdev_op_type op_type;
};
16.2.5. Device & Queues Management
After initialization, devices are in a stopped state, so must be started by the application. If an application is finished using a device it can close the device. Once closed, it cannot be restarted.
int rte_bbdev_start(uint16_t dev_id)
int rte_bbdev_stop(uint16_t dev_id)
int rte_bbdev_close(uint16_t dev_id)
int rte_bbdev_queue_start(uint16_t dev_id, uint16_t queue_id)
int rte_bbdev_queue_stop(uint16_t dev_id, uint16_t queue_id)
By default, all queues are started when the device is started, but they can be stopped individually.
int rte_bbdev_queue_start(uint16_t dev_id, uint16_t queue_id)
int rte_bbdev_queue_stop(uint16_t dev_id, uint16_t queue_id)
16.2.6. Logical Cores, Memory and Queues Relationships
The bbdev poll mode device driver library supports NUMA architecture, in which a processor’s logical cores and interfaces utilize it’s local memory. Therefore with baseband operations, the mbuf being operated on should be allocated from memory pools created in the local memory. The buffers should, if possible, remain on the local processor to obtain the best performance results and buffer descriptors should be populated with mbufs allocated from a mempool allocated from local memory.
The run-to-completion model also performs better, especially in the case of virtual bbdev devices, if the baseband operation and data buffers are in local memory instead of a remote processor’s memory. This is also true for the pipe-line model provided all logical cores used are located on the same processor.
Multiple logical cores should never share the same queue for enqueuing operations or dequeuing operations on the same bbdev device since this would require global locks and hinder performance. It is however possible to use a different logical core to dequeue an operation on a queue pair from the logical core which it was enqueued on. This means that a baseband burst enqueue/dequeue APIs are a logical place to transition from one logical core to another in a packet processing pipeline.
16.3. Device Operation Capabilities
Capabilities (in terms of operations supported, max number of queues, etc.) identify what a bbdev is capable of performing that differs from one device to another. For the full scope of the bbdev capability see the definition of the structure in the DPDK API Reference.
struct rte_bbdev_op_cap;
A device reports its capabilities when registering itself in the bbdev framework. With the aid of this capabilities mechanism, an application can query devices to discover which operations within the 3GPP physical layer they are capable of performing. Below is an example of the capabilities for a PMD it supports in relation to Turbo Encoding and Decoding operations.
static const struct rte_bbdev_op_cap bbdev_capabilities[] = {
{
.type = RTE_BBDEV_OP_TURBO_DEC,
.cap.turbo_dec = {
.capability_flags =
RTE_BBDEV_TURBO_SUBBLOCK_DEINTERLEAVE |
RTE_BBDEV_TURBO_POS_LLR_1_BIT_IN |
RTE_BBDEV_TURBO_NEG_LLR_1_BIT_IN |
RTE_BBDEV_TURBO_CRC_TYPE_24B |
RTE_BBDEV_TURBO_DEC_TB_CRC_24B_KEEP |
RTE_BBDEV_TURBO_EARLY_TERMINATION,
.max_llr_modulus = 16,
.num_buffers_src = RTE_BBDEV_TURBO_MAX_CODE_BLOCKS,
.num_buffers_hard_out =
RTE_BBDEV_TURBO_MAX_CODE_BLOCKS,
.num_buffers_soft_out = 0,
}
},
{
.type = RTE_BBDEV_OP_TURBO_ENC,
.cap.turbo_enc = {
.capability_flags =
RTE_BBDEV_TURBO_CRC_24B_ATTACH |
RTE_BBDEV_TURBO_CRC_24A_ATTACH |
RTE_BBDEV_TURBO_RATE_MATCH |
RTE_BBDEV_TURBO_RV_INDEX_BYPASS,
.num_buffers_src = RTE_BBDEV_TURBO_MAX_CODE_BLOCKS,
.num_buffers_dst = RTE_BBDEV_TURBO_MAX_CODE_BLOCKS,
}
},
RTE_BBDEV_END_OF_CAPABILITIES_LIST()
};
16.3.1. Capabilities Discovery
Discovering the features and capabilities of a bbdev device poll mode driver
is achieved through the rte_bbdev_info_get() function.
int rte_bbdev_info_get(uint16_t dev_id, struct rte_bbdev_info *dev_info)
This allows the user to query a specific bbdev PMD and get all the device
capabilities. The rte_bbdev_info structure provides two levels of
information:
Device relevant information, like: name and related rte_bus.
Driver specific information, as defined by the
struct rte_bbdev_driver_infostructure, this is where capabilities reside along with other specifics like: maximum queue sizes and priority level.
struct rte_bbdev_info {
int socket_id;
const char *dev_name;
const struct rte_device *device;
uint16_t num_queues;
bool started;
struct rte_bbdev_driver_info drv;
};
16.4. Operation Processing
Scheduling of baseband operations on DPDK’s application data path is
performed using a burst oriented asynchronous API set. A queue on a bbdev
device accepts a burst of baseband operations using enqueue burst API. On physical
bbdev devices the enqueue burst API will place the operations to be processed
on the device’s hardware input queue, for virtual devices the processing of the
baseband operations is usually completed during the enqueue call to the bbdev
device. The dequeue burst API will retrieve any processed operations available
from the queue on the bbdev device, from physical devices this is usually
directly from the device’s processed queue, and for virtual device’s from a
rte_ring where processed operations are placed after being processed on the
enqueue call.
16.4.1. Enqueue / Dequeue Burst APIs
The burst enqueue API uses a bbdev device identifier and a queue
identifier to specify the bbdev device queue to schedule the processing on.
The num_ops parameter is the number of operations to process which are
supplied in the ops array of rte_bbdev_*_op structures.
The enqueue function returns the number of operations it actually enqueued for
processing, a return value equal to num_ops means that all packets have been
enqueued.
uint16_t rte_bbdev_enqueue_enc_ops(uint16_t dev_id, uint16_t queue_id,
struct rte_bbdev_enc_op **ops, uint16_t num_ops)
uint16_t rte_bbdev_enqueue_dec_ops(uint16_t dev_id, uint16_t queue_id,
struct rte_bbdev_dec_op **ops, uint16_t num_ops)
The dequeue API uses the same format as the enqueue API of processed but
the num_ops and ops parameters are now used to specify the max processed
operations the user wishes to retrieve and the location in which to store them.
The API call returns the actual number of processed operations returned, this
can never be larger than num_ops.
uint16_t rte_bbdev_dequeue_enc_ops(uint16_t dev_id, uint16_t queue_id,
struct rte_bbdev_enc_op **ops, uint16_t num_ops)
uint16_t rte_bbdev_dequeue_dec_ops(uint16_t dev_id, uint16_t queue_id,
struct rte_bbdev_dec_op **ops, uint16_t num_ops)
16.4.2. Operation Representation
An encode bbdev operation is represented by rte_bbdev_enc_op structure,
and by rte_bbdev_dec_op for decode. These structures act as metadata
containers for all necessary information required for the bbdev operation to be
processed on a particular bbdev device poll mode driver.
struct rte_bbdev_enc_op {
int status;
struct rte_mempool *mempool;
void *opaque_data;
union {
struct rte_bbdev_op_turbo_enc turbo_enc;
struct rte_bbdev_op_ldpc_enc ldpc_enc;
}
};
struct rte_bbdev_dec_op {
int status;
struct rte_mempool *mempool;
void *opaque_data;
union {
struct rte_bbdev_op_turbo_dec turbo_enc;
struct rte_bbdev_op_ldpc_dec ldpc_enc;
}
};
The operation structure by itself defines the operation type. It includes an operation status, a reference to the operation specific data, which can vary in size and content depending on the operation being provisioned. It also contains the source mempool for the operation, if it is allocated from a mempool.
If bbdev operations are allocated from a bbdev operation mempool, see next section, there is also the ability to allocate private memory with the operation for applications purposes.
Application software is responsible for specifying all the operation specific
fields in the rte_bbdev_*_op structure which are then used by the bbdev PMD
to process the requested operation.
16.4.3. Operation Management and Allocation
The bbdev library provides an API set for managing bbdev operations which utilize the Mempool Library to allocate operation buffers. Therefore, it ensures that the bbdev operation is interleaved optimally across the channels and ranks for optimal processing.
struct rte_mempool *
rte_bbdev_op_pool_create(const char *name, enum rte_bbdev_op_type type,
unsigned int num_elements, unsigned int cache_size,
int socket_id)
rte_bbdev_*_op_alloc_bulk() and rte_bbdev_*_op_free_bulk() are used to
allocate bbdev operations of a specific type from a given bbdev operation mempool.
int rte_bbdev_enc_op_alloc_bulk(struct rte_mempool *mempool,
struct rte_bbdev_enc_op **ops, uint16_t num_ops)
int rte_bbdev_dec_op_alloc_bulk(struct rte_mempool *mempool,
struct rte_bbdev_dec_op **ops, uint16_t num_ops)
rte_bbdev_*_op_free_bulk() is called by the application to return an
operation to its allocating pool.
void rte_bbdev_dec_op_free_bulk(struct rte_bbdev_dec_op **ops,
unsigned int num_ops)
void rte_bbdev_enc_op_free_bulk(struct rte_bbdev_enc_op **ops,
unsigned int num_ops)
16.4.4. BBDEV Inbound/Outbound Memory
The bbdev operation structure contains all the mutable data relating to performing Turbo and LDPC coding on a referenced mbuf data buffer. It is used for either encode or decode operations.
FEC |
In |
Out |
|---|---|---|
Turbo Encode |
input |
output |
Turbo Decode |
input |
hard output |
soft output (optional) |
||
LDPC Encode |
input |
output |
LDPC Decode |
input |
hard output |
HQ combine (optional) |
HQ combine (optional) |
|
soft output (optional) |
It is expected that the application provides input and output mbuf pointers allocated and ready to use.
The baseband framework supports FEC coding on Code Blocks (CB) and Transport Blocks (TB).
For the output buffer(s), the application is required to provide an allocated and free mbuf, to which the resulting output will be written.
The support of split “scattered” buffers is a driver-specific feature, so it is reported individually by the supporting driver as a capability.
Input and output data buffers are identified by rte_bbdev_op_data structure,
as follows:
struct rte_bbdev_op_data {
struct rte_mbuf *data;
uint32_t offset;
uint32_t length;
};
This structure has three elements:
data: This is the mbuf data structure representing the data for BBDEV operation.This mbuf pointer can point to one Code Block (CB) data buffer or multiple CBs contiguously located next to each other. A Transport Block (TB) represents a whole piece of data that is divided into one or more CBs. Maximum number of CBs can be contained in one TB is defined by
RTE_BBDEV_(TURBO/LDPC)MAX_CODE_BLOCKS.An mbuf data structure cannot represent more than one TB. The smallest piece of data that can be contained in one mbuf is one CB. An mbuf can include one contiguous CB, subset of contiguous CBs that are belonging to one TB, or all contiguous CBs that belong to one TB.
If a BBDEV PMD supports the extended capability “Scatter-Gather”, then it is capable of collecting (gathering) non-contiguous (scattered) data from multiple locations in the memory. This capability is reported by the capability flags:
RTE_BBDEV_TURBO_ENC_SCATTER_GATHER,RTE_BBDEV_TURBO_DEC_SCATTER_GATHER,RTE_BBDEV_LDPC_ENC_SCATTER_GATHER,RTE_BBDEV_LDPC_DEC_SCATTER_GATHER.
Chained mbuf data structures are only accepted if a BBDEV PMD supports this feature. A chained mbuf can represent one non-contiguous CB or multiple non-contiguous CBs. The first mbuf segment in the given chained mbuf represents the first piece of the CB. Offset is only applicable to the first segment.
lengthis the total length of the CB.BBDEV driver is responsible for identifying where the split is and enqueue the split data to its internal queues.
If BBDEV PMD does not support this feature, it will assume inbound mbuf data contains one segment.
The output mbuf data though is always one segment, even if the input was a chained mbuf.
offset: This is the starting point of the BBDEV (encode/decode) operation, in bytes.BBDEV starts to read data past this offset. In case of chained mbuf, this offset applies only to the first mbuf segment.
length: This is the total data length to be processed in one operation, in bytes.In case the mbuf data is representing one CB, this is the length of the CB undergoing the operation. If it is for multiple CBs, this is the total length of those CBs undergoing the operation. If it is for one TB, this is the total length of the TB under operation. In case of chained mbuf, this data length includes the lengths of the “scattered” data segments undergoing the operation.
16.4.5. BBDEV Turbo Encode Operation
struct rte_bbdev_op_turbo_enc {
struct rte_bbdev_op_data input;
struct rte_bbdev_op_data output;
uint32_t op_flags;
uint8_t rv_index;
uint8_t code_block_mode;
union {
struct rte_bbdev_op_enc_cb_params cb_params;
struct rte_bbdev_op_enc_tb_params tb_params;
};
};
The Turbo encode structure includes the input and output mbuf
data pointers. The provided mbuf pointer of input needs to be big
enough to stretch for extra CRC trailers.
Parameter |
Description |
|---|---|
input |
input CB or TB data |
output |
rate matched CB or TB output buffer |
op_flags |
bitmask of all active operation capabilities |
rv_index |
redundancy version index [0..3] |
code_block_mode |
code block or transport block mode |
cb_params |
code block specific parameters (code block mode only) |
tb_params |
transport block specific parameters (transport block mode only) |
The encode interface works on both the code block (CB) and the transport block (TB). An operation executes in “CB-mode” when the CB is standalone. While “TB-mode” executes when an operation performs on one or multiple CBs that belong to a TB. Therefore, a given data can be standalone CB, full-size TB or partial TB. Partial TB means that only a subset of CBs belonging to a bigger TB are being enqueued.
NOTE: It is assumed that all enqueued ops in one
rte_bbdev_enqueue_enc_ops()call belong to one mode, either CB-mode or TB-mode.
In case that the TB is smaller than Z (6144 bits), then effectively the TB = CB. CRC24A is appended to the tail of the CB. The application is responsible for calculating and appending CRC24A before calling BBDEV in case that the underlying driver does not support CRC24A generation.
In CB-mode, CRC24A/B is an optional operation.
The CB parameter k is the size of the CB (this maps to K as described
in 3GPP TS 36.212 section 5.1.2), this size is inclusive of CRC24A/B.
The length is inclusive of CRC24A/B and equals to k in this case.
Not all BBDEV PMDs are capable of CRC24A/B calculation. Flags
RTE_BBDEV_TURBO_CRC_24A_ATTACH and RTE_BBDEV_TURBO_CRC_24B_ATTACH
informs the application with relevant capability. These flags can be set in the
op_flags parameter to indicate to BBDEV to calculate and append CRC24A/B
to CB before going forward with Turbo encoding.
Output format of the CB encode will have the encoded CB in e size output
(this maps to E described in 3GPP TS 36.212 section 5.1.4.1.2). The output mbuf
buffer size needs to be big enough to hold the encoded buffer of size e.
In TB-mode, CRC24A is assumed to be pre-calculated and appended to the inbound TB mbuf data buffer. The output mbuf data structure is expected to be allocated by the application with enough room for the output data.
The difference between the partial and full-size TB is that we need to know the
index of the first CB in this group and the number of CBs contained within.
The first CB index is given by r but the number of the remaining CBs is
calculated automatically by BBDEV before passing down to the driver.
The number of remaining CBs should not be confused with c. c is the
total number of CBs that composes the whole TB (this maps to C as
described in 3GPP TS 36.212 section 5.1.2).
The length is total size of the CBs inclusive of any CRC24A and CRC24B in
case they were appended by the application.
The case when one CB belongs to TB and is being enqueued individually to BBDEV, this case is considered as a special case of partial TB where its number of CBs is 1. Therefore, it requires to get processed in TB-mode.
The figure below visualizes the encoding of CBs using BBDEV interface in TB-mode. CB-mode is a reduced version, where only one CB exists:
Fig. 16.2 Turbo encoding of Code Blocks in mbuf structure
16.4.6. BBDEV Turbo Decode Operation
struct rte_bbdev_op_turbo_dec {
struct rte_bbdev_op_data input;
struct rte_bbdev_op_data hard_output;
struct rte_bbdev_op_data soft_output;
uint32_t op_flags;
uint8_t rv_index;
uint8_t iter_min:4;
uint8_t iter_max:4;
uint8_t iter_count;
uint8_t ext_scale;
uint8_t num_maps;
uint8_t code_block_mode;
union {
struct rte_bbdev_op_dec_cb_params cb_params;
struct rte_bbdev_op_dec_tb_params tb_params;
};
};
The Turbo decode structure includes the input, hard_output and
optionally the soft_output mbuf data pointers.
Parameter |
Description |
|---|---|
input |
virtual circular buffer, wk, size 3*Kpi for each CB |
hard output |
hard decisions buffer, decoded output, size K for each CB |
soft output |
soft LLR output buffer (optional) |
op_flags |
bitmask of all active operation capabilities |
rv_index |
redundancy version index [0..3] |
iter_max |
maximum number of iterations to perform in decode all CBs |
iter_min |
minimum number of iterations to perform in decoding all CBs |
iter_count |
number of iterations to performed in decoding all CBs |
ext_scale |
scale factor on extrinsic info (5 bits) |
num_maps |
number of MAP engines to use in decode |
code_block_mode |
code block or transport block mode |
cb_params |
code block specific parameters (code block mode only) |
tb_params |
transport block specific parameters (transport block mode only) |
Similarly, the decode interface works on both the code block (CB) and the transport block (TB). An operation executes in “CB-mode” when the CB is standalone. While “TB-mode” executes when an operation performs on one or multiple CBs that belong to a TB. Therefore, a given data can be standalone CB, full-size TB or partial TB. Partial TB means that only a subset of CBs belonging to a bigger TB are being enqueued.
NOTE: It is assumed that all enqueued ops in one
rte_bbdev_enqueue_dec_ops()call belong to one mode, either CB-mode or TB-mode.
The CB parameter k is the size of the decoded CB (this maps to K as described in
3GPP TS 36.212 section 5.1.2), this size is inclusive of CRC24A/B.
The length is inclusive of CRC24A/B and equals to k in this case.
The input encoded CB data is the Virtual Circular Buffer data stream, wk, with the null padding included as described in 3GPP TS 36.212 section 5.1.4.1.2 and shown in 3GPP TS 36.212 section 5.1.4.1 Figure 5.1.4-1. The size of the virtual circular buffer is 3*Kpi, where Kpi is the 32 byte aligned value of K, as specified in 3GPP TS 36.212 section 5.1.4.1.1.
Each byte in the input circular buffer is the LLR value of each bit of the original CB.
hard_output is a mandatory capability that all BBDEV PMDs support. This is
the decoded CBs of K sizes (CRC24A/B is the last 24-bit in each decoded CB).
Soft output is an optional capability for BBDEV PMDs. Setting flag
RTE_BBDEV_TURBO_DEC_TB_CRC_24B_KEEP in op_flags directs BBDEV to retain
CRC24B at the end of each CB. This might be useful for the application in debug
mode.
An LLR rate matched output is computed in the soft_output buffer structure
for the given CB parameter e size (this maps to E described in
3GPP TS 36.212 section 5.1.4.1.2). The output mbuf buffer size needs to be big
enough to hold the encoded buffer of size e.
The first CB Virtual Circular Buffer (VCB) index is given by r but the
number of the remaining CB VCBs is calculated automatically by BBDEV before
passing down to the driver.
The number of remaining CB VCBs should not be confused with c. c is the
total number of CBs that composes the whole TB (this maps to C as
described in 3GPP TS 36.212 section 5.1.2).
The length is total size of the CBs inclusive of any CRC24A and CRC24B in
case they were appended by the application.
The case when one CB belongs to TB and is being enqueued individually to BBDEV, this case is considered as a special case of partial TB where its number of CBs is 1. Therefore, it requires to get processed in TB-mode.
The output mbuf data structure is expected to be allocated by the application with enough room for the output data.
The figure below visualizes the decoding of CBs using BBDEV interface in TB-mode. CB-mode is a reduced version, where only one CB exists:
Fig. 16.3 Turbo decoding of Code Blocks in mbuf structure
16.4.7. BBDEV LDPC Encode Operation
The operation flags that can be set for each LDPC encode operation are given below.
NOTE: The actual operation flags that may be used with a specific BBDEV PMD are dependent on the driver capabilities as reported via
rte_bbdev_info_get(), and may be a subset of those below.
Description of LDPC encode capability flags |
|---|
|
|
|
|
|
|
|
|
The structure passed for each LDPC encode operation is given below,
with the operation flags forming a bitmask in the op_flags field.
struct rte_bbdev_op_ldpc_enc {
struct rte_bbdev_op_data input;
struct rte_bbdev_op_data output;
uint32_t op_flags;
uint8_t rv_index;
uint8_t basegraph;
uint16_t z_c;
uint16_t n_cb;
uint8_t q_m;
uint16_t n_filler;
uint8_t code_block_mode;
union {
struct rte_bbdev_op_enc_ldpc_cb_params cb_params;
struct rte_bbdev_op_enc_ldpc_tb_params tb_params;
};
};
The LDPC encode parameters are set out in the table below.
Parameter |
Description |
|
|---|---|---|
input |
input CB or TB data |
|
output |
rate matched CB or TB output buffer |
|
op_flags |
bitmask of all active operation capabilities |
|
rv_index |
redundancy version index [0..3] |
|
basegraph |
Basegraph 1 or 2 |
|
z_c |
Zc, LDPC lifting size |
|
n_cb |
Ncb, length of the circular buffer in bits. |
|
q_m |
Qm, modulation order {2,4,6,8,10} |
|
n_filler |
number of filler bits |
|
code_block_mode |
code block or transport block mode |
|
op_flags |
bitmask of all active operation capabilities |
|
cb_params |
code block specific parameters (code block mode only) |
|
e |
E, length of the rate matched output sequence in bits |
|
tb_params |
transport block specific parameters (transport block mode only) |
|
c |
number of CBs in the TB or partial TB |
|
r |
index of the first CB in the inbound mbuf data |
|
c_ab |
number of CBs that use Ea before switching to Eb |
|
ea |
Ea, length of the RM output sequence in bits, r < cab |
|
eb |
Eb, length of the RM output sequence in bits, r >= cab |
|
The mbuf input input is mandatory for all BBDEV PMDs and is the
incoming code block or transport block data.
The mbuf output output is mandatory and is the encoded CB(s). In
CB-mode ut contains the encoded CB of size e (E in 3GPP TS 38.212
section 6.2.5). In TB-mode it contains multiple contiguous encoded CBs
of size ea or eb.
The output buffer is allocated by the application with enough room
for the output data.
The encode interface works on both a code block (CB) and a transport block (TB) basis.
NOTE: All enqueued ops in one
rte_bbdev_enqueue_enc_ops()call belong to one mode, either CB-mode or TB-mode.
The valid modes of operation are:
CB-mode: one CB (attach CRC24B if required)
CB-mode: one CB making up one TB (attach CRC24A if required)
TB-mode: one or more CB of a partial TB (attach CRC24B(s) if required)
TB-mode: one or more CB of a complete TB (attach CRC24AB(s) if required)
In CB-mode if RTE_BBDEV_LDPC_CRC_24A_ATTACH is set then CRC24A
is appended to the CB. If RTE_BBDEV_LDPC_CRC_24A_ATTACH is not
set the application is responsible for calculating and appending CRC24A
before calling BBDEV. The input data mbuf length is inclusive of
CRC24A/B where present and is equal to the code block size K.
In TB-mode, CRC24A is assumed to be pre-calculated and appended to the
inbound TB data buffer, unless the RTE_BBDEV_LDPC_CRC_24A_ATTACH
flag is set when it is the responsibility of BBDEV. The input data
mbuf length is total size of the CBs inclusive of any CRC24A and
CRC24B in the case they were appended by the application.
Not all BBDEV PMDs may be capable of CRC24A/B calculation. Flags
RTE_BBDEV_LDPC_CRC_24A_ATTACH and RTE_BBDEV_LDPC_CRC_24B_ATTACH
inform the application of the relevant capability. These flags can be set
in the op_flags parameter to indicate BBDEV to calculate and append
CRC24A to CB before going forward with LDPC encoding.
The difference between the partial and full-size TB is that BBDEV needs
the index of the first CB in this group and the number of CBs in the group.
The first CB index is given by r but the number of the CBs is
calculated by BBDEV before signalling to the driver.
The number of CBs in the group should not be confused with c, the
total number of CBs in the full TB (C as per 3GPP TS 38.212 section 5.2.2)
Figure Fig. 16.2 above showing the Turbo encoding of CBs using BBDEV interface in TB-mode is also valid for LDPC encode.
16.4.8. BBDEV LDPC Decode Operation
The operation flags that can be set for each LDPC decode operation are given below.
NOTE: The actual operation flags that may be used with a specific BBDEV PMD are dependent on the driver capabilities as reported via
rte_bbdev_info_get(), and may be a subset of those below.
Description of LDPC decode capability flags |
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The structure passed for each LDPC decode operation is given below,
with the operation flags forming a bitmask in the op_flags field.
struct rte_bbdev_op_ldpc_dec {
struct rte_bbdev_op_data input;
struct rte_bbdev_op_data hard_output;
struct rte_bbdev_op_data soft_output;
struct rte_bbdev_op_data harq_combined_input;
struct rte_bbdev_op_data harq_combined_output;
uint32_t op_flags;
uint8_t rv_index;
uint8_t basegraph;
uint16_t z_c;
uint16_t n_cb;
uint8_t q_m;
uint16_t n_filler;
uint8_t iter_max;
uint8_t iter_count;
uint8_t code_block_mode;
union {
struct rte_bbdev_op_dec_ldpc_cb_params cb_params;
struct rte_bbdev_op_dec_ldpc_tb_params tb_params;
};
};
The LDPC decode parameters are set out in the table below.
Parameter |
Description |
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|---|---|---|
input |
input CB or TB data |
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hard_output |
hard decisions buffer, decoded output |
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soft_output |
soft LLR output buffer (optional) |
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harq_comb_input |
HARQ combined input buffer (optional) |
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harq_comb_output |
HARQ combined output buffer (optional) |
|
op_flags |
bitmask of all active operation capabilities |
|
rv_index |
redundancy version index [0..3] |
|
basegraph |
Basegraph 1 or 2 |
|
z_c |
Zc, LDPC lifting size |
|
n_cb |
Ncb, length of the circular buffer in bits. |
|
q_m |
Qm, modulation order {1,2,4,6,8} from pi/2-BPSK to 256QAM |
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n_filler |
number of filler bits |
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iter_max |
maximum number of iterations to perform in decode all CBs |
|
iter_count |
number of iterations performed in decoding all CBs |
|
code_block_mode |
code block or transport block mode |
|
op_flags |
bitmask of all active operation capabilities |
|
cb_params |
code block specific parameters (code block mode only) |
|
e |
E, length of the rate matched output sequence in bits |
|
tb_params |
transport block specific parameters (transport block mode only) |
|
c |
number of CBs in the TB or partial TB |
|
r |
index of the first CB in the inbound mbuf data |
|
c_ab |
number of CBs that use Ea before switching to Eb |
|
ea |
Ea, length of the RM output sequence in bits, r < cab |
|
eb |
Eb, length of the RM output sequence in bits r >= cab |
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The mbuf input input encoded CB data is mandatory for all BBDEV PMDs
and is the Virtual Circular Buffer data stream with null padding.
Each byte in the input circular buffer is the LLR value of each bit of
the original CB.
The mbuf output hard_output is mandatory and is the decoded CBs size
K (CRC24A/B is the last 24-bit in each decoded CB).
The mbuf output soft_output is optional and is an LLR rate matched
output of size e (this is E as per 3GPP TS 38.212 section 6.2.5).
The mbuf input harq_combine_input is optional and is a buffer with
the input to the HARQ combination function of the device. If the
capability RTE_BBDEV_LDPC_INTERNAL_HARQ_MEMORY_IN_ENABLE is set
then the HARQ is stored in memory internal to the device and not visible
to BBDEV.
The mbuf output harq_combine_output is optional and is a buffer for
the output of the HARQ combination function of the device. If the
capability RTE_BBDEV_LDPC_INTERNAL_HARQ_MEMORY_OUT_ENABLE is set
then the HARQ is stored in memory internal to the device and not visible
to BBDEV.
Note
More explicitly for a typical usage of HARQ retransmission in a VRAN application using a HW PMD, there will be 2 cases.
For 1st transmission, only the HARQ output is enabled:
the harq_combined_output.offset is provided to a given address. ie. typically an integer index * 32K, where the index is tracked by the application based on code block index for a given UE and HARQ process.
the related operation flag would notably include RTE_BBDEV_LDPC_HQ_COMBINE_OUT_ENABLE and RTE_BBDEV_LDPC_HARQ_6BIT_COMPRESSION.
note that no explicit flush or reset of the memory is required.
For 2nd transmission, an input is also required to benefit from HARQ combination gain:
the changes mentioned above are the same (note that rvIndex may be adjusted).
the operation flag would additionally include the LDPC_HQ_COMBINE_IN_ENABLE flag.
the harq_combined_input.offset must be set to the address of the related code block (ie. same as the harq_combine_output index above for the same code block, HARQ process, UE).
the harq_combined_input.length must be set to the length which was provided back in the related harq_combined_output.length when it has processed and dequeued (previous HARQ iteration).
The output mbuf data structures are expected to be allocated by the application with enough room for the output data.
As with the LDPC encode, the decode interface works on both a code block (CB) and a transport block (TB) basis.
NOTE: All enqueued ops in one
rte_bbdev_enqueue_dec_ops()call belong to one mode, either CB-mode or TB-mode.
The valid modes of operation are:
CB-mode: one CB (check CRC24B if required)
CB-mode: one CB making up one TB (check CRC24A if required)
TB-mode: one or more CB making up a partial TB (check CRC24B(s) if required)
TB-mode: one or more CB making up a complete TB (check CRC24B(s) if required)
The mbuf length is inclusive of CRC24A/B where present and is equal
the code block size K.
The first CB Virtual Circular Buffer (VCB) index is given by r but the
number of the remaining CB VCBs is calculated automatically by BBDEV
and passed down to the driver.
The number of remaining CB VCBs should not be confused with c, the
total number of CBs in the full TB (C as per 3GPP TS 38.212 section 5.2.2)
The length is total size of the CBs inclusive of any CRC24A and CRC24B in
case they were appended by the application.
Figure Fig. 16.3 above showing the Turbo decoding of CBs using BBDEV interface in TB-mode is also valid for LDPC decode.
16.5. Sample code
The baseband device sample application gives an introduction on how to use the bbdev framework, by giving a sample code performing a loop-back operation with a baseband processor capable of transceiving data packets.
The following sample C-like pseudo-code shows the basic steps to encode several buffers using (sw_turbo) bbdev PMD.
/* EAL Init */
ret = rte_eal_init(argc, argv);
if (ret < 0)
rte_exit(EXIT_FAILURE, "Invalid EAL arguments\n");
/* Get number of available bbdev devices */
nb_bbdevs = rte_bbdev_count();
if (nb_bbdevs == 0)
rte_exit(EXIT_FAILURE, "No bbdevs detected!\n");
/* Create bbdev op pools */
bbdev_op_pool[RTE_BBDEV_OP_TURBO_ENC] =
rte_bbdev_op_pool_create("bbdev_op_pool_enc",
RTE_BBDEV_OP_TURBO_ENC, NB_MBUF, 128, rte_socket_id());
/* Get information for this device */
rte_bbdev_info_get(dev_id, &info);
/* Setup BBDEV device queues */
ret = rte_bbdev_setup_queues(dev_id, qs_nb, info.socket_id);
if (ret < 0)
rte_exit(EXIT_FAILURE,
"ERROR(%d): BBDEV %u not configured properly\n",
ret, dev_id);
/* setup device queues */
qconf.socket = info.socket_id;
qconf.queue_size = info.drv.queue_size_lim;
qconf.op_type = RTE_BBDEV_OP_TURBO_ENC;
for (q_id = 0; q_id < qs_nb; q_id++) {
/* Configure all queues belonging to this bbdev device */
ret = rte_bbdev_queue_configure(dev_id, q_id, &qconf);
if (ret < 0)
rte_exit(EXIT_FAILURE,
"ERROR(%d): BBDEV %u queue %u not configured properly\n",
ret, dev_id, q_id);
}
/* Start bbdev device */
ret = rte_bbdev_start(dev_id);
/* Create the mbuf mempool for pkts */
mbuf_pool = rte_pktmbuf_pool_create("bbdev_mbuf_pool",
NB_MBUF, MEMPOOL_CACHE_SIZE, 0,
RTE_MBUF_DEFAULT_BUF_SIZE, rte_socket_id());
if (mbuf_pool == NULL)
rte_exit(EXIT_FAILURE,
"Unable to create '%s' pool\n", pool_name);
while (!global_exit_flag) {
/* Allocate burst of op structures in preparation for enqueue */
if (rte_bbdev_enc_op_alloc_bulk(bbdev_op_pool[RTE_BBDEV_OP_TURBO_ENC],
ops_burst, op_num) != 0)
continue;
/* Allocate input mbuf pkts */
ret = rte_pktmbuf_alloc_bulk(mbuf_pool, input_pkts_burst, MAX_PKT_BURST);
if (ret < 0)
continue;
/* Allocate output mbuf pkts */
ret = rte_pktmbuf_alloc_bulk(mbuf_pool, output_pkts_burst, MAX_PKT_BURST);
if (ret < 0)
continue;
for (j = 0; j < op_num; j++) {
/* Append the size of the ethernet header */
rte_pktmbuf_append(input_pkts_burst[j],
sizeof(struct rte_ether_hdr));
/* set op */
ops_burst[j]->turbo_enc.input.offset =
sizeof(struct rte_ether_hdr);
ops_burst[j]->turbo_enc->input.length =
rte_pktmbuf_pkt_len(bbdev_pkts[j]);
ops_burst[j]->turbo_enc->input.data =
input_pkts_burst[j];
ops_burst[j]->turbo_enc->output.offset =
sizeof(struct rte_ether_hdr);
ops_burst[j]->turbo_enc->output.data =
output_pkts_burst[j];
}
/* Enqueue packets on BBDEV device */
op_num = rte_bbdev_enqueue_enc_ops(qconf->bbdev_id,
qconf->bbdev_qs[q], ops_burst,
MAX_PKT_BURST);
/* Dequeue packets from BBDEV device*/
op_num = rte_bbdev_dequeue_enc_ops(qconf->bbdev_id,
qconf->bbdev_qs[q], ops_burst,
MAX_PKT_BURST);
}
16.5.1. BBDEV Device API
The bbdev Library API is described in the DPDK API Reference document.