RapidIO II IP Core Transmits Unintended link-request Control Symbols

Description

Writing the value 3’b100 to the COMMAND field of the RapidIO II IP core Port 0 Link Maintenance Request CSR at offset 0x140 should cause the RapidIO II IP core to transmit a single link-request control symbol with the cmd field value of input-status.

However, writing this value in fact triggers transmission of multiple link-request input-status control symbols.

Resolution

The RapidIO Protocol Specifications, Revision 2.2 requires that reading this register return the most recent written value. However, until this issue is fixed you can avoid the transmission of unbounded numbers of link-request input-status control symbols by resetting the COMMAND field of the register after you write the value 3’b100. After you do so, you must ensure that the software does not read the Port 0 Link Maintenance Request CSR to determine its most recent written value after the IP core transmits a link-request input-status control symbol and before it transmits the next link-request reset-device control symbol.

This issue will be fixed in a future version of the RapidIO II MegaCore function.