Texas Instruments TMS320DM36X manual Example 2. Receive Buffer Descriptor in C Structure Format

www.ti.com Architecture

Example 2. Receive Buffer Descriptor in C Structure Format

/*

//EMAC Descriptor

//The following is the format of a single buffer descriptor

//on the EMAC.

*/
typedef struct _EMAC_Desc {
struct _EMAC_Desc *pNext;		/* Pointer to next descriptor in chain	*/
Uint8	*pBuffer;	/* Pointer to data buffer	*/
Uint32	BufOffLen;	/* Buffer Offset(MSW) and Length(LSW)	*/
Uint32	PktFlgLen;	/* Packet Flags(MSW) and Length(LSW)	*/

} EMAC_Desc;
/* Packet Flags	*/
#define EMAC_DSC_FLAG_SOP	0x80000000u
#define EMAC_DSC_FLAG_EOP	0x40000000u
#define EMAC_DSC_FLAG_OWNER	0x20000000u
#define EMAC_DSC_FLAG_EOQ	0x10000000u
#define EMAC_DSC_FLAG_TDOWNCMPLT	0x08000000u
#define EMAC_DSC_FLAG_PASSCRC	0x04000000u
#define EMAC_DSC_FLAG_JABBER	0x02000000u
#define EMAC_DSC_FLAG_OVERSIZE	0x01000000u
#define EMAC_DSC_FLAG_FRAGMENT	0x00800000u
#define EMAC_DSC_FLAG_UNDERSIZED	0x00400000u
#define EMAC_DSC_FLAG_CONTROL	0x00200000u
#define EMAC_DSC_FLAG_OVERRUN	0x00100000u
#define EMAC_DSC_FLAG_CODEERROR	0x00080000u
#define EMAC_DSC_FLAG_ALIGNERROR	0x00040000u
#define EMAC_DSC_FLAG_CRCERROR	0x00020000u
#define EMAC_DSC_FLAG_NOMATCH	0x00010000u

2.6.5.3Buffer Offset

This 16-bit field must be initialized to zero by the software application before adding the descriptor to a receive queue.

Whether or not this field is updated depends on the setting of the RXBUFFEROFFSET register. When the offset register is set to a non-zero value, the received packet is written to the packet buffer at an offset given by the value of the register, and this value is also written to the buffer offset field of the descriptor.

When a packet is fragmented over multiple buffers because it does not fit in the first buffer supplied, the buffer offset only applies to the first buffer in the list, which is where the start of packet (SOP) flag is set in the corresponding buffer descriptor. In other words, the buffer offset field is only updated by the EMAC on SOP descriptors.

The range of legal values for the BUFFEROFFSET register is 0 to (Buffer Length – 1) for the smallest value of buffer length for all descriptors in the list.

SPRUFI5B –March 2009 –Revised December 2010 Ethernet Media Access Controller (EMAC)/Management Data Input/Output 27

Submit Documentation Feedback (MDIO)

© 2009–2010, Texas Instruments Incorporated