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update width documentation #89

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eab5fc4
width documentation update
Dec 18, 2025
a3b0c29
update documentation
Dec 18, 2025
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7 changes: 6 additions & 1 deletion docs/source/Configuration/Routers.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,8 @@ Payload Width

A router can specify its internal ``payloadWidth``. When routers with different payload
widths are connected by a channel, Constellation will autogenerate width-adapters
on the channels if the widths are multiples of each other.
on the channels if the widths are multiples of each other. A width-adapter either segments
a packet into more flits or merge several flits of a packet into one.



Expand All @@ -99,6 +100,10 @@ on the channels if the widths are multiples of each other.
| | |
+-------------------------------------------------------------------------+--------------------+

.. Note:: When merging, the width adapter requires each packet to contain a number of flits
that is a multiple of the merging ratio. For example, when up-scaling from 64 bits to
128 bits, the width adapter expects the packet to consist of a multiple of 2 flits.


Virtual Channel Allocator
^^^^^^^^^^^^^^^^^^^^^^^^^
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8 changes: 2 additions & 6 deletions docs/source/Configuration/Terminals.rst
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Expand Up @@ -34,14 +34,10 @@ will auto-generate width converters to either further segment or merge flits.
+-------------------------------------------------------------------------+--------------------+
| .. code:: scala | |terminal_width| |
| | |
| ingresses = Seq(UserIngressParams(0), payloadBits=128)), | |
| egresses = Seq( UserEgressParams(0), payloadBits=128)), | |
| ingresses = Seq(UserIngressParams(0, payloadBits=128)), | |
| egresses = Seq( UserEgressParams(1, payloadBits=128)), | |
| routers = (i) => UserRouterParams(payloadBits=64), | |
| | |
+-------------------------------------------------------------------------+--------------------+

.. Note:: The common use case for ``payloadWidth`` is to set the same width for all terminals.

.. Warning:: Be wary of using payload width converters liberally. For example, a 3-flit packet of
64 bits per flit, if up-scaled to a 2-flit packet of 128 bits per flit, will be
down-scaled into a 4-flit packet of 64 bits per flit.