Texas Instruments TMS320C645x DSP - Manual (Page 30)

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2.5.4 Transmit Buffer Descriptor Format
EMAC Functional Architecture
A transmit (TX) buffer descriptor ( Figure 9 ) 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 9. Transmit Descriptor Format
(a) Word 0
31 0
Next Descriptor Pointer
(b) Word 1
31 0
Buffer Pointer
(c) Word 2
31 16 15 0
Buffer Offset Buffer Length
(d) Word 3
31 30 29 28 27 26 25 16
SOP EOP OWNER EOQ TDOWN PASS Reserved
CMPLT CRC
15 0
Packet Length
Example 1. Transmit 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
30 Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO) SPRU975B – August 2006
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