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== History ==
== Introduction ==
This White Paper document describes a practical application of the asymmetric multi-processing (AMP) configuration illustrated [[AN-BELK-001:_Asymmetric_Multiprocessing_(AMP)_on_Bora_–_Linux_FreeRTOS|here]] [a]. Specifically, this approach has been used to implement a non-intrusive continuous link monitoring mechanism for the Xilinx Zynq multi-gigabit serial transceivers [b]. The starting point for this work is represented by the Xilinx Application Notes
XAPP743<ref name="XAPP743"> Mike Jenkins, David Mahashin, ''XAPP743 (v1.0.1) Eye Scan with MicroBlaze Processor MCS'', 28th October 2013''</ref>
and
with Vivado IP Integrator and AXI4'', 19th November 2014</ref>, thus reading of these documents is highly recommended.
The issue that this White Paper technical note addresses is the need of monitoring multi-gigabit transceivers link status when operating on the field [c] in a <u>non-intrusive way</u>. Just imagine a product that is based on the architecture similar to the one depicted in the following figure. It is assumed that this architecture is quite representative of many real use cases.
A generic communication IP is implemented in Programmable Logic (PL) . This IP makes use of multi-gigabit transceivers to communicate with the peer at the other end of the physical link. On Processor Subsystem (PS) side, Linux operating system is used. On top of the kernel, several applications run, implementing high-level product's functionalities, including the management of sent and received data through the link shown in the figure. It is also assumed that the reliability of this link is a crucial factor for the successful product functioning. Thus a specific monitoring of its health has to be implemented in order to detect any deviation from normal working conditions that may affect link robustness such as:
*medium/long-term drift of the physical link characteristics
*significant part to part variations of such characteristics.
[a] At the time of this writing, [[AN-BELK-001:_Asymmetric_Multiprocessing_(AMP)_on_Bora_–_Linux_FreeRTOS|this document]] refers to BORA only. However , the same AMP implementation is available for BORA Xpress as well.
[b] More complex configurations such as [[BRX-WP001:_Real-timeness,_system_integrity_and_TrustZone®_technology_on_AMP_configuration|this one]] can be used as well.
[[#REQ1|REQ1]] through [[#REQ4|REQ4]] specify in detail a generic requirement of ''non-intrusiveness''. In other words, it is required that the implementation of link monitoring function is virtually transparent to the other parts of the system. As a consequence
*<u>application software dondoesn't need any change when adding such functionality</u>
*<u>the cost of additional PL resources is neglectable</u> with respect to the Microblaze-based approach described in <ref name="XAPP743"></ref>
*<u>physical link is not affected at all</u>: normal operating, while monitoring is continuously in progress, is guaranteed by the integrated circuitry of GTP/GTX transceivers<ref name="UG482">''UG482 7 Series FPGAs GTP Transceivers User Guide'', http://www.xilinx.com/support/documentation/user_guides/ug482_7Series_GTP_Transceivers.pdf</ref><ref name="UG476">''UG476 7 Series FPGAs GTX/GTH Transceivers User Guide'', http://www.xilinx.com/support/documentation/user_guides/ug476_7Series_Transceivers.pdf</ref>.
