NEC Network Controller uPD98502 - Manual (Page 257)

CHAPTER 4 ATM CELL PROCESSOR
Preliminary User’s Manual S15543EJ1V0UM 257
4.7 Commands
Here, basic commands used in AAL-5 operation are described. Other commands used in AAL-2, OAM and cell
switching functions are described in µµµµPD98502 Application Note (to be planned).
ATM Cell Processor provides V
R
4120A with the following basic commands.
Table 4-3. Commands
Command What this block does
Set_Link_Rate Set PHY Link Rate
Open_Channel Reserves VC table area in Work RAM.
Close_Channel Releases VC table area.
Tx_Ready Starts transmission process.
Add_Buffers Add Buffer Directories to the indicated pool
Indirect_Access Enables V R 4120A RISC Processor to access Work RAM
All commands are written in command register (A_CMR) and command extension register (A_CER) by V
R
4120A.
Command register has busy flag. Since ATM Cell Processor only proceeds one command at a time, it sets the busy
flag when it accepts the command. V R 4120A cannot issue another command while this busy flag is 1. When finish the
command operation, ATM Cell Processor sets the busy flag to 0. V R 4120A has to read the busy flag of the command
register and checks if busy bit is 0, before issues new command.
(1) Commands which ATM Cell Processor returns command indication
When ATM Cell Processor receives Open_Channel, Close_Channel, Open_IP_Channel, Close_IP_Channel,
Tx_Ready and Add_Buffers command, it writes command indication in command register. V R 4120A RISC
Processor has to read command indication, after issuing these commands. However, while busy flag is 1, ATM
Cell Processor has not finished command processing yet, so that, V
R
4120A RISC Processor has to wait until
busy flag in command register becomes 0 in order to read the indication.
(2) Commands which command extension register is used
Indirect_Access command and Add_Buffers command use command extended register.
When V R 4120A writes these commands, V R 4120A has to write to command extension register first, and then
command register. ATM Cell Processor starts command operation after command register is written. So that,
unless command extension register is written first, the information in command extension register is ignored by
ATM Cell Processor.
When command extension register is used for getting information from ATM Cell Processor, V R 4120A writes to
command register and wait until busy flag in command register becomes a ‘0’, and reads command extended register.