74 wiersze
2.3 KiB
Plaintext
74 wiersze
2.3 KiB
Plaintext
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repetier communication protocol
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Why a new protocol?
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The current reprap communication is just sending the gcode string to the reprap.
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If communication is to slow, the printer waits. If communication fails very
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strange things can happen, depending on the detection of the error. The current
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checksum method is not very secure. I've seen errors with correct checksums.
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The last disadvantage is the required parsing. It is for an arduino quite
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time consuming.
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What is better in this protocol?
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1. Data is send in binary form, no need for number conversion
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2. Binary format is shorter. We can transfer more commands with the same
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bandwidth.
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3. Improved checksum validation.
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Comparison of sizes:
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Command 1:
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G1 E10810.1 F1000
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Original size: 21 Bytes
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Updated for errorcheck:
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N6654 G1 E10810.1 F1000 *65
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Errorcheck size: 29 Bytes
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repetier-protocol: 15 Bytes
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Command 2:
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G1 X69.4864 Y48.1169 E10813.1 F2400
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Original size: 36 Bytes
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Updated for errorcheck:
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N7665 G1 X69.4864 Y48.1169 E10813.1 F2400 *78
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Errorcheck size: 56 Bytes
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Repetier-protocol:23 Bytes
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As you can see, this protocol reduces the average data transfered to
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less then 50%.
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Gcode Letter to Bit and Datatype:
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N : Bit 0 : 16-Bit Integer
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M : Bit 1 : 8-Bit unsigned byte
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G : Bit 2 : 8-Bit unsigned byte
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X : Bit 3 : 32-Bit Float
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Y : Bit 4 : 32-Bit Float
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Z : Bit 5 : 32-Bit Float
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E : Bit 6 : 32-Bit Float
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: Bit 7 : always set to distinguish binary from ASCII line.
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F : Bit 8 : 32-Bit Float
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T : Bit 9 : 8 Bit Integer
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S : Bit 10 : 16 Bit Value
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P : Bit 11 : 32 Bit Integer
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Text : Bit 15 : 8 Bit size + Data
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A GCode line is transformed into a binary parameterization.
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16 bit integer with given parameter set
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if bit 0 set: 16 bit linenumber
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if bit 1 set: 8 bit M value
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if bit 2 set: 8 bit G value
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if bit 3 set: 32 bit floatpoint X value
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if bit 4 set: 32 bit floatpoint Y value
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if bit 5 set: 32 bit floatpoint Z value
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if bit 6 set: 32 bit floatpoint E value
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if bit 7 set: 32 bit floatpoint F value
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if bit 8 set: 8 bit T value
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if bit 9 set: 8 bit string length + string data
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16 Bit checksum
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The checksum is computed by Fletcher-16 checksum algorithm.
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See http://en.wikipedia.org/wiki/Fletcher's_checksum
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Advantage: We build checksum over checksum and both bytes are 0 if
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correct.
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The maximum size for a command without string is 2+2+3+5*4+2=29 Byte.
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