Texas Instruments TMS320DM646x manual Transmit Buffer Descriptor Format

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Architecture

2.5.4Transmit Buffer Descriptor Format

A transmit (TX) buffer descriptor (Figure 7) is a contiguous block of four 32-bit data words aligned on a 32-bit boundary that describes a packet or a packet fragment. Example 1 shows the transmit buffer descriptor described by a C structure.

				Figure 7. Transmit Buffer Descriptor Format
Word 0
31							0
					Next Descriptor Pointer
Word 1
31							0
					Buffer Pointer
Word 2
31					16	15	0
			Buffer Offset				Buffer Length
Word 3
31	30	29	28	27	26	25	16
SOP	EOP	OWNER	EOQ	TDOWNCMPLT	PASSCRC		Reserved
15							0
					Packet Length

Example 1. Transmit 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

24	Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO)	SPRUEQ6–December 2007
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