TDA4VM: scatter/gather operations on c7x

Akhil,

Here we go....

Some info available on using the Scatter-gather feature.

For more info please refer :- 4.6. ENET — Platform Development Kit (PDK) - JACINTO User Guide

When you install processor SDK RTOS for J721e, https://www.ti.com/tool/PROCESSOR-SDK-J721E

you will find the user guide in the following path..

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\ti-processor-sdk-rtos-j721e-evm-08_06_01_03.tar\ti-processor-sdk-rtos-j721e-evm-08_06_01_03\pdk_jacinto_08_06_01_03\docs\userguide\jacinto\modules\enet.html

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4.6.2.1.2. Scatter-Gather

Starting in SDK 8.5, Enet LLD provides support for UDMA scatter-gather feature for packet transmission only. Scatter-gather is currently not supported for packet reception.

There are Enet LLD API changes introduced for scatter-gather which break compatibility with previous SDKs. The main changes in the parameters used by the application to pass the Ethernet frame buffer and the buffer length to the driver.

For the sake of comparison with previous API, let’s consider the case of a single continuous buffer (i.e. number of scatter segments of 1).

The application can pass up to four segments for packet transmission as defined by ENET_UDMA_CPSW_MAX_SG_LIST. It’s worth noting that Enet LLD uses the same EnetDma_PktInfo type for packet reception but only a single segment is enforced as scatter-gather for packet reception is currently not enabled.

The scatter-gather list information is provided by the application to the driver via EnetUdma_PktInfo::sgList parameter of the packet info structure. Application must set the number of segments (EnetUdma_PktInfo::sgList.numScatterSegments), and the buffer pointer and length of each segment in EnetUdma_PktInfo::sgList.list[] array.

The relevant structures are shown below:

/*! Scatter gather list entry */
typedef struct EnetUdma_SGListEntry_s
{
    /*! Pointer to scatter fragment */
    uint8_t *bufPtr;
    /*! Length of valid data in the scatter fragment */
    uint32_t segmentFilledLen;
    /*! Length of allocated buffer for scatter fragment */
    uint32_t segmentAllocLen;
} EnetUdma_SGListEntry;

/*! Packet scatter list info */
typedef struct EnetUdma_SGList_s
{
    /*! Number of valid scatter segments in the packet */
    uint32_t numScatterSegments;
    /*! Array of scatterList having info on each individual scatter segement */
    EnetUdma_SGListEntry list[ENET_UDMA_CPSW_MAX_SG_LIST];
} EnetUdma_SGList;

/*! Packet data structure */
typedef struct EnetUdma_PktInfo_s
{
    ...
    /*! Scatter Gather list information for packets to be transmitted. */
    EnetUdma_SGList sgList;
} EnetUdma_PktInfo;

/*! Opaque handle that represents a DMA packet */
typedef struct EnetUdma_PktInfo_s EnetDma_Pkt;

Scatter-gather for packet transmission is also enabled in Enet LLD integration with lwIP stack. Note that LWIP_NETIF_TX_SINGLE_PBUF must be disabled for lwIP to pass multiple segments to the adaptation layer and to the Enet driver.

Scatter-gather feature is enabled by default in Enet LLD loopback test and lwIP example applications.

Regards

Shankari G