Protocols - Revision history

Mizapf at 10:34, 2 August 2016

2016-08-02T10:34:56Z

← Older revision		Revision as of 10:34, 2 August 2016
Line 13:		Line 13:
	The last block may require padding if the number of remaining bytes does not suffice to fill the block.		The last block may require padding if the number of remaining bytes does not suffice to fill the block.

	Each block contains a sequence number. When a block with the same number as the previous one is received, the receiver accepts the block for the same position and sends back an ACK. This situation may have been caused by a previously lost ACK. If the block number is not the expected next one or a repetition of the recent one, the sequence is out of sync, and the receiver shall send a CAN in order to terminate the protocol.		Each block contains a sequence number. When a block with the same number as the previous one is received, the receiver accepts the block for the same position and sends back an ACK (0x06). This situation may have been caused by a previously lost ACK. If the block number is not the expected next one or a repetition of the recent one, the sequence is out of sync, and the receiver shall send a CAN (0x18) in order to terminate the protocol.

	{\| class="xmodemseq"		{\| class="xmodemseq"
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	\| Block		\| Block
	\|		\|
	\| EOT		\| EOT (04)
	\|		\|
	\|-		\|-
	! Receiver sending		! Receiver sending
	\| NAK		\| NAK (15)
	\|		\|
	\| ACK		\| ACK (06)
	\|		\|
	\| ACK		\| ACK (06)
	\|		\|
	\| ...		\| ...
	\|		\|
	\| ACK		\| ACK (06)
	\|		\|
	\| ACK		\| ACK (06)
	\|}		\|}

	The receiver has a timeout of 10 seconds, after which it transmits a NAK. The message sequence starts with the receiver sending the first timeout NAK to the sender, which may be sent immediately. All errors are retried for at most 10 times.		The receiver has a timeout of 10 seconds, after which it transmits a NAK (0x15). The message sequence starts with the receiver sending the first timeout NAK to the sender, which may be sent immediately. All errors are retried for at most 10 times.

	A NAK must be sent by the receiver if the block data are invalid.		A NAK must be sent by the receiver if the block data are invalid.
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	! 1		! 1
	\|-		\|-
	\| SOH		\| SOH (01)
	\| Number		\| Number
	\| /Number		\| /Number
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	\|-		\|-
	! Receiver sending		! Receiver sending
	\| "C"		\| "C" (43)
	\|		\|
	\| ACK		\| ACK
Line 132:		Line 132:
	! 2		! 2
	\|-		\|-
	\| STX		\| STX (02)
	\| Number		\| Number
	\| /Number		\| /Number

Mizapf: /* XModem protocol */

2011-05-08T20:03:35Z

XModem protocol

← Older revision		Revision as of 20:03, 8 May 2011
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	The last block may require padding if the number of remaining bytes does not suffice to fill the block.		The last block may require padding if the number of remaining bytes does not suffice to fill the block.

	Each block contains a sequence number. When a block with the same number as the previous one is received, the receiver ~~ignores~~ the block.		Each block contains a sequence number. When a block with the same number as the previous one is received, the receiver accepts the block for the same position and sends back an ACK. This situation may have been caused by a previously lost ACK. If the block number is not the expected next one or a repetition of the recent one, the sequence is out of sync, and the receiver shall send a CAN in order to terminate the protocol.

	{\| class="xmodemseq"		{\| class="xmodemseq"
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	The receiver has a timeout of 10 seconds, after which it transmits a NAK. The message sequence starts with the receiver sending the first timeout NAK to the sender, which may be sent immediately. All errors are retried for at most 10 times.		The receiver has a timeout of 10 seconds, after which it transmits a NAK. The message sequence starts with the receiver sending the first timeout NAK to the sender, which may be sent immediately. All errors are retried for at most 10 times.

	A NAK must be sent by the receiver if the block data are invalid~~. If the block number is not the expected next one or a repetition of the recent one, the sequence is out of sync, and the receiver shall send a CAN~~.		A NAK must be sent by the receiver if the block data are invalid.

	=== Standard XModem ===		=== Standard XModem ===

Mizapf at 16:27, 8 May 2011

2011-05-08T16:27:04Z

@@ Line 68: / Line 68: @@
 The checksum field contains the least significant byte of the sum of the data bytes of this block.
 === XModem/CRC ===
@@ Line 129: / Line 109: @@
 ! 1
 ! 1
-! style="width:300px" | 128/1024
+! style="width:200px" | 128
 ! 2
 |-
-| SOH/STX
+| SOH
 | Number
 | /Number
@@ Line 140: / Line 120: @@
 In general it is reasonable to have the sender start in CRC mode and wait for the receiver's first message.

Mizapf at 22:25, 7 May 2011

2011-05-07T22:25:05Z

← Older revision		Revision as of 22:25, 7 May 2011
Line 1:		Line 1:
	~~== Communication with devices ==~~

	~~Here is a commented log when [[SSSD Format Log\|formatting a SSSD floppy disk]] with the TI disk controller. Actually, this dump was achieved using MESS and putting in some printf lines.~~


	== XModem protocol ==		== XModem protocol ==

Mizapf: /* XModem/CRC */

2011-05-07T21:59:37Z

XModem/CRC

← Older revision		Revision as of 21:59, 7 May 2011
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	! 1		! 1
	! 1		! 1
	! style="width:~~200px~~" \| 128		! style="width:300px" \| 128/1024
	! 2		! 2
	\|-		\|-
	\| SOH		\| SOH/STX
	\| Number		\| Number
	\| /Number		\| /Number

Mizapf at 21:58, 7 May 2011

2011-05-07T21:58:53Z

← Older revision		Revision as of 21:58, 7 May 2011
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	\|}		\|}

	The sender may switch between 128-byte and 1024-byte blocks after receiving an ACK from the receiver.		The sender may switch between 128-byte and 1024-byte blocks after receiving an ACK from the receiver. The sender should start with 1K blocks and check for the receiver's response, either as NAK or ACK.

	=== XModem/CRC ===		=== XModem/CRC ===
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	\|}		\|}

	In general it is reasonable to have the sender start in CRC mode and wait for the receiver's first message~~. Also, the sender should start with 1K blocks and check for the receiver's response, either as NAK or ACK~~.		In general it is reasonable to have the sender start in CRC mode and wait for the receiver's first message.

Mizapf at 21:58, 7 May 2011

2011-05-07T21:58:10Z

← Older revision		Revision as of 21:58, 7 May 2011
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	\| ACK		\| ACK
	\|}		\|}

			If the sender does not support XModem/CRC it keeps silent, and the receiver shall retry for some time. After that it sends a NAK to switch back to normal XModem.

	The blocks have this layout:		The blocks have this layout:
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	\| CRC16		\| CRC16
	\|}		\|}

			In general it is reasonable to have the sender start in CRC mode and wait for the receiver's first message. Also, the sender should start with 1K blocks and check for the receiver's response, either as NAK or ACK.

Mizapf at 21:45, 7 May 2011

2011-05-07T21:45:36Z

← Older revision		Revision as of 21:45, 7 May 2011
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	In this variant, a more powerful checksum algorithm is used, the CRC16 algorithm. In order to negotiate this variant for both sender and receiver, the receiver sends a "C" as the first message instead of the NAK.		In this variant, a more powerful checksum algorithm is used, the CRC16 algorithm. In order to negotiate this variant for both sender and receiver, the receiver sends a "C" as the first message instead of the NAK.

			{\| class="xmodemseq"
			! Sender sending
			\|
			\| Block
			\|
			\| Block
			\|
			\| ...
			\|
			\| Block
			\|
			\| EOT
			\|
			\|-
			! Receiver sending
			\| "C"
			\|
			\| ACK
			\|
			\| ACK
			\|
			\| ...
			\|
			\| ACK
			\|
			\| ACK
			\|}

			The blocks have this layout:

	{\| class="xmodem"		{\| class="xmodem"

Mizapf at 21:43, 7 May 2011

2011-05-07T21:43:07Z

@@ Line 19: / Line 19: @@
 Each block contains a sequence number. When a block with the same number as the previous one is received, the receiver ignores the block.
 {| class="xmodemseq"
@@ Line 51: / Line 47: @@
 | ACK
 |}
 === Standard XModem ===
@@ Line 70: / Line 70: @@
 |}
-The number is a sequence number which increases by one for each successive block. The /Number field is the one's complement of the Number field and calculates as 255-Number. When the number reaches 256 it is reset to 0.
+The number is a sequence number which increases by one for each successive block. The first block starts at 1. The /Number field is the one's complement of the Number field and calculates as 255-Number. When the number reaches 256 it is reset to 0.
 The checksum field contains the least significant byte of the sum of the data bytes of this block.
@@ Line 95: / Line 95: @@
 === XModem/CRC ===

Mizapf at 21:33, 7 May 2011

2011-05-07T21:33:01Z

← Older revision		Revision as of 21:33, 7 May 2011
Line 20:		Line 20:
	Each block contains a sequence number. When a block with the same number as the previous one is received, the receiver ignores the block.		Each block contains a sequence number. When a block with the same number as the previous one is received, the receiver ignores the block.

	The message sequence starts with the receiver sending the first timeout NAK to the sender.		The receiver has a timeout of 10 seconds, after which it transmits a NAK. The message sequence starts with the receiver sending the first timeout NAK to the sender, which may be sent immediately. All errors are retried for at most 10 times.

			A NAK must be sent by the receiver if the block data are invalid. If the block number is not the expected next one or a repetition of the recent one, the sequence is out of sync, and the receiver shall send a CAN.

	{\| class="xmodemseq"		{\| class="xmodemseq"
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	\|		\|
	\| Block		\| Block
			\|
			\| ...
			\|
			\| Block
			\|
			\| EOT
			\|
	\|-		\|-
	! Receiver sending		! Receiver sending
	\| NAK		\| NAK
	\|		\|
			\| ACK
			\|
			\| ACK
			\|
			\| ...
			\|
	\| ACK		\| ACK
	\|		\|
	\| ACK		\| ACK
	\|}		\|}


	~~The receiver has a timeout of 10 seconds, after which it transmits a NAK.~~


	=== Standard XModem ===		=== Standard XModem ===