DP83905AVQB datasheet(47/80 Pages) NSC

47 / 80 page

60 Operation of ATLANTIC Controller (Continued)

4 Clear the ATLANTIC Controller’s Remote Byte Count

registers (RBCR0 and RBCR1)

5 Read the stored value of the TXP bit from step 1

above

If this value is a 0 set the ‘‘Resend’’ variable toa0and

jump to step 6

If this value is a 1 read the ATLANTIC Controller’s

Interrupt Status Register If either the Packet Transmit-

ted bit (PTX) or Transmit Error bit (TXE) is set to a 1 set

the ‘‘Resend’’ variable to a 0 and jump to step 6 If

neither of these bits is set place a 1 in the ‘‘Resend’’

variable and jump to step 6

This step determines if there was a transmission in

progress when the stop command was issued in step 2

If there was a transmission in progress the ATLANTIC

Controller’s ISR is read to determine whether or not the

packet was recognized by the ATLANTIC Controller If

neither the PTX nor TXE bit was set then the packet

will essentially be lost and re-transmitted only after a

time-out takes place in the upper level software By de-

termining that the packet was lost at the driver level a

transmit command can be reissued to the ATLANTIC

Controller once the overflow routine is completed (as in

step 11) Also it is possible for the ATLANTIC Control-

ler to defer indefinitely when it is stopped on a busy

network Step 5 also alleviates this problem Step 5 is

essential and should not be omitted from the overflow

routine in order for the ATLANTIC Controller to oper-

ate correctly

6 Place the ATLANTIC Controller in either mode 1 or

mode 2 Ioopback This can be accomplished by setting

bits D2 and D1 of the Transmit Configuration Register

to 01 or 10 respectively

7 Issue the START command to the ATLANTIC Control-

ler This can be accomplished by Writing 22H to the

Command Register This is necessary to activate the

ATLANTIC Controller’s Remote DMA channel

8 Remove one or more packets from the receive buffer

ring

9 Reset the overwrite warning (OVW overflow) bit in the

Interrupt Status Register

10 Take the ATLANTIC Controller out of loopback This is

done by Writing the Transmit Configuration Register

with the value it contains during normal operation (Bits

D2 and D1 should both be programmed to 0)

11 lf the ‘‘Resend’’ variable is set to a 1 reset the ‘‘Re-

send’’ variable and reissue the transmit command This

is done by writing a value of 26H to the Command Reg-

ister If the ‘‘Resend’’ variable is 0 nothing needs to be

done

Note 1

If Remote DMA is not being used the ATLANTIC Controller does

not need to be started before packets can be removed from the

receive buffer ring Hence step 8 could be done before step 7

eliminating or reducing the time spent polling in step 5

Note 2

When the ATLANTIC Controller is in STOP mode the Missed

Packet Tally counter is disabled

TLF11498 – 29

FIGURE 32 Overflow Routine

DP83905AVQB Datasheet(PDF) 47 Page - National Semiconductor (TI)

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