Altera RapidIO MegaCore Function - Manual (Page 102)

4–56 Chapter 4: Functional Description
Logical Layer Modules
RapidIO MegaCore Function August 2014 Altera Corporation
User Guide
An outbound message that times out before its response is received is treated in the
same manner as an outbound message that receives an error response: if enabled, an
interrupt is generated by the Error Management module by asserting the
sys_mnt_s_irq
signal, and the ERROR_CODE field in the Tx Doorbell Completion
Status register ( Table 6–64 ) is set to indicate the error.
If the interrupt is not enabled, the Avalon-MM master must periodically poll the Tx
Doorbell
Completion Status register to check for available completed messages
before retrieving them from the Tx Completion FIFO.
DOORBELL request packets for which RETRY responses are received are resent by
hardware automatically. No retry limit is imposed on outbound DOORBELL messages.
Doorbell Message Reception
DOORBELL request packets received from the Transport layer module are stored in an
internal buffer, and an interrupt is generated on the DOORBELL Avalon-MM slave
interface, if the interrupt is enabled.
The corresponding interrupt status bit is set every time a DOORBELL request packet is
received and resets itself when the Rx FIFO is empty. Software can clear the interrupt
status bit by writing a 1 to this specific bit location of the Doorbell Interrupt Status
register (
Table 6–67 ).
An interrupt is generated when a valid response packet is received and when a
request packet is received. Therefore, when the interrupt is generated, you must check
the Doorbell Interrupt Status register to determine the type of event that triggered
the interrupt.
If the interrupt is not enabled, the external Avalon-MM master must periodically poll
the Rx Doorbell Status register (
Table 6–59 ) to check the number of available
messages before retrieving them from the Rx doorbell buffer.
Appropriate Type 13 response packets are generated internally and sent for all the
received DOORBELL messages. A response with DONE status is generated when the
received DOORBELL packet can be processed immediately. A response with RETRY status
is generated to defer processing the received message when the internal hardware is
busy, for example when the Rx doorbell buffer is full.
Avalon-ST Pass-Through Interface
The Avalon-ST pass-through interface is an optional interface that is generated when
you select the Avalon-ST pass-through interface in the Transport and Maintenance
page of the RapidIO parameter editor (refer to
“Enable Avalon-ST Pass-Through
Interface” on page 3–4 ). If destination ID checking is enabled, all packets received by
the Transport layer whose destination ID does not match this RapidIO IP core’s base
device
ID or whose ftype is not supported by this IP core’s variation are routed to the
Rx Avalon-ST pass-through interface. If you disable destination ID checking, request
packets are instead routed to the Rx Avalon-ST pass-through interface only if they
have ftypes that are not supported by this IP core’s variation. After packets are routed
to the Rx Avalon-ST pass-through interface, they can be further examined by a local
processor or parsed and processed by a custom user function.
The following applications can use the Avalon-ST pass-through interface: