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SDB - Self-describing Bus
Commit 24ad104e authored by Wesley W. Terpstra's avatar Wesley W. Terpstra Committed by Alessandro Rubini
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fixes to tech errors and heavy political language

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docs/specification/proposal.tex
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...@@ -30,9 +30,11 @@ ...@@ -30,9 +30,11 @@
\parskip10pt \parskip10pt
\makesavenoteenv{tabular} \makesavenoteenv{tabular}
\title{Self Description Structures for Logic Cores} \title{Self-Describing Bus (SDB) Specification\\
\author{Manohar Vanga (BE/CO/HT), Wesley Terpstra (GSI),\\ for Logic Cores}
Alessandro Rubini (Independent Consultant)} \author{Alessandro Rubini (Consultant for CERN)\\
Wesley Terpstra (GSI),\\
Manohar Vanga (CERN, BE/CO/HT)}
\date{June 20th 2012} \date{June 20th 2012}
\begin{document} \begin{document}
...@@ -86,8 +88,8 @@ hardware and software resources allow a richer description of logic blocks. ...@@ -86,8 +88,8 @@ hardware and software resources allow a richer description of logic blocks.
We are also aware of the PCI and USB data structures, but they are We are also aware of the PCI and USB data structures, but they are
unsuitable for an FPGA, either. First of all, they assume devices are unsuitable for an FPGA, either. First of all, they assume devices are
enumerated by other means whereas we need to be able to scan a flat enumerated by other means whereas we need to be able to scan a flat
address space; then, their vendor ID space is ridiculously small address space; then, their vendor ID space is not wide enough to allow
because the model of the respective consortia is based on artificial scarcity. small developers to easily participate.
This specification, thus, uses 64 bits for the vendor ID, to prevent scarcity. This specification, thus, uses 64 bits for the vendor ID, to prevent scarcity.
The vendor space is split in two parts, and all users are free to bless their The vendor space is split in two parts, and all users are free to bless their
...@@ -101,14 +103,10 @@ are officially assigned and published. The vendor registry, however, is not ...@@ -101,14 +103,10 @@ are officially assigned and published. The vendor registry, however, is not
part of this specification, which just lists the first few vendor-ID values that part of this specification, which just lists the first few vendor-ID values that
have already been used. have already been used.
All multi-byte values are stored in \textit{big endian} order. This All multi-byte values are stored in \textit{big endian} order. We need
choice is taken in order to make life easier for some developers (the poor a well-defined endianness to allow generic scanning of the target bus;
guys and dolls that sometimes need to look at binary dumps one byte at a time) we picked bigendian because most embedded devices are big endian and
and to make life harder for other developers (the poor guys and dolls that work because it is the format usually chosen by existing standards documents.
on the PC and think all the world is \textit{little endian}). Actually,
by choosing the less common endianness we aim for code to be more
portable, because code ignoring byte ordering will simply not work
when compiled on the most common platforms.
All data structures are 64 byte in size and they are all similar in their All data structures are 64 byte in size and they are all similar in their
internal layout; the last byte in the 64-byte slot identifies the type internal layout; the last byte in the 64-byte slot identifies the type
...@@ -120,11 +118,9 @@ driver may reside in a very simple soft-core. ...@@ -120,11 +118,9 @@ driver may reside in a very simple soft-core.
\subsection{Scope of This Specification} \subsection{Scope of This Specification}
This specification is not \textit{official} in any way: it just This specification documents the format used by CERN and GSI. However,
documents what we are doing and why we do it like this. We believe everyone is welcome to use the data structures defined in this
in free circulation of ideas and we think the good ones will flourish. specification (or customized derivatives) in their own work.
Everybody is welcome to use the data structures defined in this specification
and give feedback, both positive and negative.
Parts of this document are written in the language of Parts of this document are written in the language of
a formal specification because we need clear and sharp rules in a formal specification because we need clear and sharp rules in
...@@ -224,14 +220,14 @@ structure declares the address where the self-description for the ...@@ -224,14 +220,14 @@ structure declares the address where the self-description for the
sub-bus is to be found. sub-bus is to be found.
\item[Integration] \hfill \\ \item[Integration] \hfill \\
The optional \textit{integration} product describes the aggregate bus. The optional \textit{integration} product describes an aggregate bus.
It is a \textit{product} record, not a It is a \textit{product} record, not a
\textit{component}, in that it has no associated address range. This \textit{component}, in that it has no associated address range. This
meta-information item can be used by a vendor using a standard meta-information item can be used by a vendor to describe
\textit{interconnect} logic block to declare its own its particular combination of devices, interconnect, and address layout.
identifiers and integration date for the whole FPGA design; as For example, if an expansion card uses a number of stock devices
such we expect to find it only in the description of the combined with a stock interconnect, its driver can nonetheless recognize
outer bus description level. the aggregate device by the integration record.
\item[Controller] \hfill \\ \item[Controller] \hfill \\
The \textit{controller} is a software abstraction, used in the host The \textit{controller} is a software abstraction, used in the host
...@@ -253,7 +249,7 @@ here; by identifying each instantiated device it can also drive the ...@@ -253,7 +249,7 @@ here; by identifying each instantiated device it can also drive the
remote peripherals without prior knowledge of the specific FPGA binary remote peripherals without prior knowledge of the specific FPGA binary
it is talking to. it is talking to.
The same mechanism is soon going to be used in the \textit{White The same mechanism is already part of the \textit{White
Rabbit PTP Core} and the outer-level FPGA designs that are Rabbit PTP Core} and the outer-level FPGA designs that are
being used in our synchronized I/O boards. being used in our synchronized I/O boards.
...@@ -283,7 +279,7 @@ Kernel environment. The uninterested reader can skip over to the next ...@@ -283,7 +279,7 @@ Kernel environment. The uninterested reader can skip over to the next
section where we get back to the actual structures. section where we get back to the actual structures.
In our plans this self-description standard is tightly related with In our plans this self-description standard is tightly related with
Linux device drivers, because most of oue FPGA devices are going to be Linux device drivers, because most of our FPGA devices are going to be
driven by a GNU/Linux host, whether over PCI, VME, or Etherbone. driven by a GNU/Linux host, whether over PCI, VME, or Etherbone.
Devices may appear and disappear during system lifetime: this happens Devices may appear and disappear during system lifetime: this happens
...@@ -397,7 +393,10 @@ unexpected race conditions or other inconsistencies. ...@@ -397,7 +393,10 @@ unexpected race conditions or other inconsistencies.
When user-space requests access to the whole bus, this will force When user-space requests access to the whole bus, this will force
unbinding of all the device drivers that are active over the bus. unbinding of all the device drivers that are active over the bus.
This is a shortcut over individually unbinding all drivers using This is a shortcut over individually unbinding all drivers using
\textit{sysfs} device attrobutes. \textit{sysfs} device attributes. The system will also support
a user-access mode by which the whole bus is available to
user space without passing through the unbinding phase; this is
meant as a debugging tool and must be used with great care.
\subsection{Autoprobing Device Drivers} \subsection{Autoprobing Device Drivers}
......
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