DP83916 datasheet(40/96 Pages) NSC

40 / 96 page

40 SONIC-16 Registers (Continued)

438 Transmit Registers

The transmit registers described in this section are part of

the User Register set The UTDA and CTDA must be initial-

ized prior to issuing the transmit command (setting the TXP

bit) in the Command register

Upper Transmit Descriptor Address Register (UTDA)

This register contains the upper address bits (Ak2316l)

for accessing the transmit descriptor area (TDA) and is con-

catenated with the contents of the CTDA when the SONIC-

16 accesses the TDA in system memory The TDA can be

as large as 32k words and can be located anywhere in sys-

tem memory This register is unaffected by a hardware or

software reset

Current Transmit Descriptor Address Register (CTDA)

The 16-bit CTDA register contains the lower address bits

(Ak151l) of the 23-bit transmit descriptor address During

initialization this register must be programmed with the low-

er address bits of the transmit descriptor The SONIC-16

concatenates the contents of this register with the contents

of the UTDA to point to the transmit descriptor Bit 0 of this

end of the list This register is unaffected by a hardware or

software reset

439 Receive Registers

The receive registers described in this section are part of

the User Register set A software reset has no effect on

these registers and a hardware reset only affects the EOBC

and RSC registers The receive registers must be initialized

prior to issuing the receive command (setting the RXEN bit)

in the Command register

Upper Receive Descriptor Address Register (URDA)

This register contains the upper address bits (Ak2316l)

for accessing the receive descriptor area (RDA) and is con-

catenated with the contents of the CRDA when the SONIC-

16 accesses the RDA in system memory The RDA can be

as large as 32k words and can be located anywhere in sys-

tem memory This register is unaffected by a hardware or

software reset

Current Receive Descriptor Address Register (CRDA)

The CRDA is a 16-bit readwrite register used to locate the

received packet descriptor block within the RDA It contains

the lower address bits (Ak151l) The SONIC-16 concate-

nates the contents of the CRDA with the contents of the

URDA to form the complete 23-bit address The resulting

23-bit address points to the first field of the descriptor block

Bit 0 of this register is the End of List (EOL) bit and is used

to denote the end of the list This register is unaffected by a

hardware or software reset

End of Buffer Word Count Register (EOBC)

The SONIC-

16 uses the contents of this register to determine where to

place the next packet At the end of packet reception the

SONIC-16 compares the contents of the EOBC register with

the contents of the Remaining Buffer Word Count registers

(RBWC01) to determine whether (1) to place the next

packet in the same RBA or (2) to place the next packet in

another RBA If the EOBC is less than or equal to the re-

maining number of words in the RBA after a packet is re-

ceived (ie EOBC s RBWC01) the SONIC-16 buffers the

next packet in the same RBA If the EOBC is greater than

the remaining number of words in the RBA after a packet is

received (ie EOBC l RBWC01) the Last Packet in RBA

bit LPKT in the Receive Control Register section 433 is

set and the SONIC-16 fetches the next resource descriptor

Hence the next packet received will be buffered in a new

RBA A hardware reset sets this register to 02F8H (760

words or 1520 bytes) See sections 342 and 3444 for

more information about using EOBC

Upper Receive Resource Address Register (URRA)

The

URRA is a 16-bit readwrite register It is programmed with

the base address of the receive resource area (RRA) This

8-bit upper address value (Ak2316l) locates the receive

resource area in system memory

SONIC-16 uses the

URRA register when accessing the receive descriptors with-

in the RRA by concatenating the lower address value from

one of four receive resource registers (RSA REA RWP or

RRP)

Resource Start Address Register (RSA)

The RSA is a

15-bit readwrite register The LSB is not used and always

reads back as a 0 The RSA is programmed with the lower

15-bit address (Ak151l) of the starting address of the

receive resource area SONIC-16 concatenates the con-

tents of this register with the contents of the URRA to form

the complete 23-bit address

Resource End Address Register (REA)

The REA is a

15-bit readwrite register The LSB is not used and always

reads back as a 0 The REA is programmed with the lower

15-bit address (Ak151l) of the ending address of the re-

ceive resource area SONIC-16 concatenates the contents

of this register with the contents of the URRA to form the

complete 23-bit address

Resource Read Pointer Register (RRP)

The RRP is a

15-bit readwrite register The LSB is not used and always

reads back as a 0 The RRP is programmed with the lower

15-bit address (Ak151l) of the first field of the next de-

scriptor the SONIC-16 will read SONIC-16 concatenates

the contents of this register with the contents of the URRA

to form the complete 23-bit address

Resource Write Pointer Register (RWP)

The RWP is a

15-bit readwrite register The LSB is not used and always

reads back as a 0 The RWP is programmed with the lower

15-bit address (Ak151l) of the next available location the

system can add a descriptor SONIC-16 concatenates the

contents of this register with the contents of the URRA to

form the complete 23-bit address

Receive Sequence Counter Register (RSC)

This is a

16-bit readwrite register containing two fields The SONIC-

16 uses this register to provide status information on the

number of packets within a RBA and the number of RBAs

The RSC register contains two 8-bit (modulo 256) counters

After each packet is received the packet sequence number

is incremented The SONIC-16 maintains a single sequence

number for each RBA When the SONIC-16 uses the next

RBA the packet sequence number is reset to zero and the

RBA sequence number is incremented This register is reset

to 0 by a hardware reset or by writing zero to it A software

reset has no affect

RBA Sequence Number

Packet Sequence Number

(Modulo 256)

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