SMSC COM20020 manual Transmit Command Chaining

M S B

T R I

T R I

R I

TA

P O R

T E S T

R E C O N

T M A

T M A

L S B

TTA

TTA

FIGURE 9 - COMMAND CHAINING STATUS REGISTER QUEUE

∙ Up to two outstanding transmit interrupts

COMMAND CHAINING

and two outstanding receive interrupts are

stored by the device, along with their

The Command Chaining operation allows

respective status bits.

consecutive transmissions

and

receptions to

∙ The Interrupt Mask bits act on TTA (Rising

occur without host microcontroller intervention.

Transition on

Transmitter

Available) for

Through

the use of a dual two-level

FIFO,

transmit

operations

and

TRI

(Rising

commands to be transmitted and received, as

Transition of Receiver Inhibited) for receive

well as the status bits, are pipelined.

operations. TTA is set upon completion of

In

order

for the COM20020 to

be

compatible

a packet transmission only. TRI is set upon

completion of

a

packet reception

only.

with previous SMSC ARCNET

device

drivers,

Typically there is no need to mask the TTA

the device defaults to the non-chaining mode.

and TRI bits after clearing the interrupt.

In order to take advantage of the Command

Chaining

operation,

the Command Chaining

∙

The traditional

TA and RI

bits

are still

Mode must be enabled via a logic "1" on bit 6 of

available to reflect the present status of the

the Configuration Register.

device.

In Command Chaining, the Status Register

Transmit Command Chaining

appears as in Figure 9.

The following is a list of Command Chaining

When the processor issues the first "Enable

guidelines for the software programmer. Further

Transmit to Page fnn" command, the

detail can be found in the Transmit Command

COM20020 responds in the usual manner by

Chaining and Receive Command Chaining

resetting the TA and TMA bits to prepare for the

sections.

transmission from the specified page.

The TA

bit can be used to see if there is currently a

∙

The device is designed such that the interrupt

transmission

pending,

but

the TA bit

is

really

meant to be

used

in

the

non-chaining

mode

service

routine

latency

does

not

affect

only.

The

TTA

bits provide

the

relevant

performance.

information for the device in the Command

∙

Up to two outstanding transmissions and two

Chaining mode.

outstanding receptions can be pending at any given time. The commands may be given in any order.

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