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docs: Avoid using "firmware" in the documentation

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The term "firmware" is ambiguous - it could refer to the entire
project (host and micro-controller software) or to just the
micro-controller software.  Avoid the term in the documentation.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor
2017-04-27 15:14:11 -04:00
parent d7a1111955
commit c1c0b2dd38
8 changed files with 466 additions and 455 deletions
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256
docs/Protocol.md
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@@ -1,8 +1,9 @@
The Klipper transmission protocol can be thought of, at a high level,
as a series of command and response strings that are compressed,
transmitted over a serial line, and then processed at the receiving
side. An example series of commands in uncompressed human-readable
format might look like:
The Klipper messaging protocol is used for low-level communication
between the Klipper host software and the Klipper micro-controller
software. At a high level the protocol can be thought of as a series
of command and response strings that are compressed, transmitted, and
then processed at the receiving side. An example series of commands in
uncompressed human-readable format might look like:
```
set_digital_out pin=86 value=1
@@ -12,34 +13,35 @@ queue_step oid=7 interval=7458 count=10 add=331
queue_step oid=7 interval=11717 count=4 add=1281
```
See the [firmware commands](Firmware_Commands.md) document for
information on available commands. See the [debugging](Debugging.md)
document for information on how to translate a G-Code file into its
corresponding human-readable firmware commands.
See the [mcu commands](MCU_Commands.md) document for information on
available commands. See the [debugging](Debugging.md) document for
information on how to translate a G-Code file into its corresponding
human-readable micro-controller commands.
This page provides a high-level description of the Klipper
transmission protocol itself. It describes how messages are declared,
encoded in binary format (the "compression" scheme), and transmitted.
This page provides a high-level description of the Klipper messaging
protocol itself. It describes how messages are declared, encoded in
binary format (the "compression" scheme), and transmitted.
The goal of the protocol is to enable an error-free communication
channel between the host and firmware that is low-latency,
low-bandwidth, and low-complexity for the firmware.
channel between the host and micro-controller that is low-latency,
low-bandwidth, and low-complexity for the micro-controller.
Firmware Interface
==================
Micro-controller Interface
==========================
The Klipper transmission protocol can be thought of as a
[RPC](https://en.wikipedia.org/wiki/Remote_procedure_call) mechanism
between firmware and host. The firmware declares the commands that the
host may invoke along with the response messages that it can
generate. The host uses that information to command the firmware to
perform actions and to interpret the results.
between micro-controller and host. The micro-controller software
declares the commands that the host may invoke along with the response
messages that it can generate. The host uses that information to
command the micro-controller to perform actions and to interpret the
results.
Declaring commands
------------------
The firmware declares a "command" by using the DECL_COMMAND() macro in
the C code. For example:
The micro-controller software declares a "command" by using the
DECL_COMMAND() macro in the C code. For example:
```
DECL_COMMAND(command_set_digital_out, "set_digital_out pin=%u value=%c");
@@ -48,11 +50,11 @@ DECL_COMMAND(command_set_digital_out, "set_digital_out pin=%u value=%c");
The above declares a command named "set_digital_out". This allows the
host to "invoke" this command which would cause the
command_set_digital_out() C function to be executed in the
firmware. The above also indicates that the command takes two integer
parameters. When the command_set_digital_out() C code is executed, it
will be passed an array containing these two integers - the first
corresponding to the 'pin' and the second corresponding to the
'value'.
micro-controller. The above also indicates that the command takes two
integer parameters. When the command_set_digital_out() C code is
executed, it will be passed an array containing these two integers -
the first corresponding to the 'pin' and the second corresponding to
the 'value'.
In general, the parameters are described with printf() style syntax
(eg, "%u"). The formatting directly corresponds to the human-readable
@@ -63,42 +65,42 @@ documentation. In this example, the "%c" is also used as documentation
to indicate the expected integer is 1 byte in size (the declared
integer size does not impact the parsing or encoding).
At firmware compile time, the build will collect all commands declared
with DECL_COMMAND(), determine their parameters, and arrange for them
to be callable.
The micro-controller build will collect all commands declared with
DECL_COMMAND(), determine their parameters, and arrange for them to be
callable.
Declaring responses
-------------------
To send information from the firmware to the host a "response" is
generated. These are both declared and transmitted using the sendf() C
macro. For example:
To send information from the micro-controller to the host a "response"
is generated. These are both declared and transmitted using the
sendf() C macro. For example:
```
sendf("status clock=%u status=%c", sched_read_time(), sched_is_shutdown());
```
The above transmits a "status" response message that contains two
integer parameters ("clock" and "status"). At firmware compile time
the build automatically finds all sendf() calls and generates encoders
for them. The first parameter of the sendf() function describes the
integer parameters ("clock" and "status"). The micro-controller build
automatically finds all sendf() calls and generates encoders for
them. The first parameter of the sendf() function describes the
response and it is in the same format as command declarations.
The host can arrange to register a callback function for each
response. So, in effect, commands allow the host to invoke C functions
in the firmware and responses allow the firmware to invoke code in the
host.
in the micro-controller and responses allow the micro-controller
software to invoke code in the host.
The firmware should only invoke sendf() from command or task handlers,
and it should not be invoked from interrupts or timers. The firmware
does not need to issue a sendf() in response to a received command, it
is not limited in the number of times sendf() may be invoked, and it
may invoke sendf() at any time from a task handler.
The sendf() macro should only be invoked from command or task
handlers, and it should not be invoked from interrupts or timers. The
code does not need to issue a sendf() in response to a received
command, it is not limited in the number of times sendf() may be
invoked, and it may invoke sendf() at any time from a task handler.
### Output responses
To simplify debugging, the firmware also has an output() C
function. For example:
To simplify debugging, there is also has an output() C function. For
example:
```
output("The value of %u is %s with size %u.", x, buf, buf_len);
@@ -110,15 +112,14 @@ to generate and format arbitrary messages for human consumption.
Declaring constants
-------------------
The firmware can also define constants to be exported. For example,
the following:
Constants can also be exported. For example, the following:
```
DECL_CONSTANT(SERIAL_BAUD, 250000);
```
would export a constant named "SERIAL_BAUD" with a value of 250000
from the firmware to the host.
from the micro-controller to the host.
Low-level message encoding
==========================
@@ -130,9 +131,9 @@ the transmission system.
Message Blocks
--------------
All data sent from host to firmware and vice-versa are contained in
"message blocks". A message block has a two byte header and a three
byte trailer. The format of a message block is:
All data sent from host to micro-controller and vice-versa are
contained in "message blocks". A message block has a two byte header
and a three byte trailer. The format of a message block is:
```
<1 byte length><1 byte sequence><n-byte content><2 byte crc><1 byte sync>
@@ -160,11 +161,11 @@ present in the message block content.
Message Block Contents
----------------------
Each message block sent from host to firmware contains a series of
zero or more message commands in its contents. Each command starts
with a [Variable Length Quantity](#variable-length-quantities) (VLQ)
encoded integer command-id followed by zero or more VLQ parameters for
the given command.
Each message block sent from host to micro-controller contains a
series of zero or more message commands in its contents. Each command
starts with a [Variable Length Quantity](#variable-length-quantities)
(VLQ) encoded integer command-id followed by zero or more VLQ
parameters for the given command.
As an example, the following four commands might be placed in a single
message block:
@@ -183,21 +184,22 @@ and encoded into the following eight VLQ integers:
```
In order to encode and parse the message contents, both the host and
firmware must agree on the command ids and the number of parameters
each command has. So, in the above example, both the host and firmware
would know that "id_set_digital_out" is always followed by two
parameters, and "id_get_config" and "id_get_status" have zero
parameters. The host and firmware share a "data dictionary" that maps
the command descriptions (eg, "set_digital_out pin=%u value=%c") to
their integer command-ids. When processing the data, the parser will
know to expect a specific number of VLQ encoded parameters following a
given command id.
micro-controller must agree on the command ids and the number of
parameters each command has. So, in the above example, both the host
and micro-controller would know that "id_set_digital_out" is always
followed by two parameters, and "id_get_config" and "id_get_status"
have zero parameters. The host and micro-controller share a "data
dictionary" that maps the command descriptions (eg, "set_digital_out
pin=%u value=%c") to their integer command-ids. When processing the
data, the parser will know to expect a specific number of VLQ encoded
parameters following a given command id.
The message contents for blocks sent from firmware to host follow the
same format. The identifiers in these messages are "response ids", but
they serve the same purpose and follow the same encoding rules. In
practice, message blocks sent from the firmware to the host never
contain more than one response in the message block contents.
The message contents for blocks sent from micro-controller to host
follow the same format. The identifiers in these messages are
"response ids", but they serve the same purpose and follow the same
encoding rules. In practice, message blocks sent from the
micro-controller to the host never contain more than one response in
the message block contents.
### Variable Length Quantities
@@ -229,60 +231,62 @@ the length as a VLQ encoded integer followed by the contents itself:
```
The command descriptions found in the data dictionary allow both the
host and firmware to know which command parameters use simple VLQ
encoding and which parameters use string encoding.
host and micro-controller to know which command parameters use simple
VLQ encoding and which parameters use string encoding.
Data Dictionary
===============
In order for meaningful communications to be established between
firmware and host, both sides must agree on a "data dictionary". This
data dictionary contains the integer identifiers for commands and
responses along with their descriptions.
micro-controller and host, both sides must agree on a "data
dictionary". This data dictionary contains the integer identifiers for
commands and responses along with their descriptions.
At compile time the firmware build uses the contents of DECL_COMMAND()
and sendf() macros to generate the data dictionary. The build
The micro-controller build uses the contents of DECL_COMMAND() and
sendf() macros to generate the data dictionary. The build
automatically assigns unique identifiers to each command and
response. This system allows both the host and firmware code to
seamlessly use descriptive human-readable names while still using
response. This system allows both the host and micro-controller code
to seamlessly use descriptive human-readable names while still using
minimal bandwidth.
The host queries the data dictionary when it first connects to the
firmware. Once the host downloads the data dictionary from the
firmware, it uses that data dictionary to encode all commands and to
parse all responses from the firmware. The host must therefore handle
a dynamic data dictionary. However, to keep the firmware simple, the
firmware always uses its static (compiled in) data dictionary.
micro-controller. Once the host downloads the data dictionary from the
micro-controller, it uses that data dictionary to encode all commands
and to parse all responses from the micro-controller. The host must
therefore handle a dynamic data dictionary. However, to keep the
micro-controller software simple, the micro-controller always uses its
static (compiled in) data dictionary.
The data dictionary is queried by sending "identify" commands to the
firmware. The firmware will respond to each identify command with an
"identify_response" message. Since these two commands are needed prior
to obtaining the data dictionary, their integer ids and parameter
types are hard-coded in both the firmware and the host. The
"identify_response" response id is 0, the "identify" command id
is 1. Other than having hard-coded ids the identify command and its
response are declared and transmitted the same way as other commands
and responses. No other command or response is hard-coded.
micro-controller. The micro-controller will respond to each identify
command with an "identify_response" message. Since these two commands
are needed prior to obtaining the data dictionary, their integer ids
and parameter types are hard-coded in both the micro-controller and
the host. The "identify_response" response id is 0, the "identify"
command id is 1. Other than having hard-coded ids the identify command
and its response are declared and transmitted the same way as other
commands and responses. No other command or response is hard-coded.
The format of the transmitted data dictionary itself is a zlib
compressed JSON string. The firmware compile process generates the
string, compresses it, and stores it in the text section of the
firmware. The data dictionary can be much larger than the maximum
message block size - the host downloads it by sending multiple
identify commands requesting progressive chunks of the data
compressed JSON string. The micro-controller build process generates
the string, compresses it, and stores it in the text section of the
micro-controller flash. The data dictionary can be much larger than
the maximum message block size - the host downloads it by sending
multiple identify commands requesting progressive chunks of the data
dictionary. Once all chunks are obtained the host will assemble the
chunks, uncompress the data, and parse the contents.
In addition to information on the communication protocol, the data
dictionary also contains firmware version, constants (as defined by
DECL_CONSTANT), and static strings.
dictionary also contains the software version, constants (as defined
by DECL_CONSTANT), and static strings.
Static Strings
--------------
To reduce bandwidth the data dictionary also contains a set of static
strings known to the firmware. This is useful when sending messages
from firmware to host. For example, if the firmware were to run:
strings known to the micro-controller. This is useful when sending
messages from micro-controller to host. For example, if the
micro-controller were to run:
```
shutdown("Unable to handle command");
@@ -295,22 +299,22 @@ to their associated human-readable strings.
Message flow
============
Message commands sent from host to firmware are intended to be
error-free. The firmware will check the CRC and sequence numbers in
each message block to ensure the commands are accurate and
in-order. The firmware always processes message blocks in-order -
should it receive a block out-of-order it will discard it and any
other out-of-order blocks until it receives blocks with the correct
sequencing.
Message commands sent from host to micro-controller are intended to be
error-free. The micro-controller will check the CRC and sequence
numbers in each message block to ensure the commands are accurate and
in-order. The micro-controller always processes message blocks
in-order - should it receive a block out-of-order it will discard it
and any other out-of-order blocks until it receives blocks with the
correct sequencing.
The low-level host code implements an automatic retransmission system
for lost and corrupt message blocks sent to the firmware. To
facilitate this, the firmware transmits an "ack message block" after
each successfully received message block. The host schedules a timeout
after sending each block and it will retransmit should the timeout
expire without receiving a corresponding "ack". In addition, if the
firmware detects a corrupt or out-of-order block it may transmit a
"nak message block" to facilitate fast retransmission.
for lost and corrupt message blocks sent to the micro-controller. To
facilitate this, the micro-controller transmits an "ack message block"
after each successfully received message block. The host schedules a
timeout after sending each block and it will retransmit should the
timeout expire without receiving a corresponding "ack". In addition,
if the micro-controller detects a corrupt or out-of-order block it may
transmit a "nak message block" to facilitate fast retransmission.
An "ack" is a message block with empty content (ie, a 5 byte message
block) and a sequence number greater than the last received host
@@ -325,15 +329,15 @@ in the event of transmission latency. The timeout, retransmit,
windowing, and ack mechanism are inspired by similar mechanisms in
[TCP](https://en.wikipedia.org/wiki/Transmission_Control_Protocol).
In the other direction, message blocks sent from firmware to host are
designed to be error-free, but they do not have assured
In the other direction, message blocks sent from micro-controller to
host are designed to be error-free, but they do not have assured
transmission. (Responses should not be corrupt, but they may go
missing.) This is done to keep the implementation in the firmware
simple. There is no automatic retransmission system for responses -
the high-level code is expected to be capable of handling an
occasional missing response (usually by re-requesting the content or
setting up a recurring schedule of response transmission). The
sequence number field in message blocks sent to the host is always one
greater than the last received sequence number of message blocks
received from the host. It is not used to track sequences of response
message blocks.
missing.) This is done to keep the implementation in the
micro-controller simple. There is no automatic retransmission system
for responses - the high-level code is expected to be capable of
handling an occasional missing response (usually by re-requesting the
content or setting up a recurring schedule of response
transmission). The sequence number field in message blocks sent to the
host is always one greater than the last received sequence number of
message blocks received from the host. It is not used to track
sequences of response message blocks.