Difference between revisions of "Ir:USER"

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This service was added with [[2.0.0-2]]. It employs a custom packet format with obfuscation and error detection.
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#REDIRECT [[IR Services#IR Service "ir:USER"]]
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= Command set =
 
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When sending data, SendIrnop is used when the size is <=0xFC, otherwise SendIrnopLarge is used.
 
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{| class="wikitable" border="1"
 
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|-
 
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!  Command Header
 
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!  Available since system version
 
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!  Description
 
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|-
 
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| 0x00010182
 
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| [[2.0.0-2]]
 
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| InitializeIrnop
 
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|-
 
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| 0x00020000
 
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| [[2.0.0-2]]
 
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| FinalizeIrnop
 
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|-
 
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| 0x00030000
 
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| [[2.0.0-2]]
 
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| ClearReceiveBuffer
 
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|-
 
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| 0x00040000
 
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| [[2.0.0-2]]
 
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| ClearSendBuffer
 
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|-
 
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| 0x0005....
 
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| [[2.0.0-2]]
 
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| WaitConnection
 
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|-
 
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| 0x00060040
 
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| [[2.0.0-2]]
 
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| RequireConnection (u8 input)
 
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|-
 
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| 0x0007....
 
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| [[2.0.0-2]]
 
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| AutoConnection
 
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|-
 
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| 0x0008....
 
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| [[2.0.0-2]]
 
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| AnyConnection
 
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|-
 
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| 0x00090000
 
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| [[2.0.0-2]]
 
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| Disconnect
 
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|-
 
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| 0x000A0000
 
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| [[2.0.0-2]]
 
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| GetReceiveEvent (writes event handle to cmdreply[3])
 
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|-
 
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| 0x000B0000
 
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| [[2.0.0-2]]
 
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| GetSendEvent (writes event handle to cmdreply[3])
 
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|-
 
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| 0x000C0000
 
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| [[2.0.0-2]]
 
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| GetConnectionStatusEvent (writes event handle to cmdreply[3])
 
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|-
 
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| 0x000D0042
 
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| [[2.0.0-2]]
 
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| SendIrnop (u32 size, ((Size<<14) <nowiki>|</nowiki> 2), inbufptr)
 
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|-
 
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| 0x000E0042
 
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| [[2.0.0-2]]
 
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| SendIrnopLarge (u32 size, ((Size<<8) <nowiki>|</nowiki> 10), inbufptr)
 
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|-
 
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| 0x000F....
 
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| [[2.0.0-2]]
 
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| ReceiveIrnop
 
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|-
 
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| 0x0010....
 
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| [[2.0.0-2]]
 
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| ReceiveIrnopLarge
 
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|-
 
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| 0x0011....
 
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| [[2.0.0-2]]
 
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| GetLatestReceiveErrorResult
 
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|-
 
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| 0x0012....
 
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| [[2.0.0-2]]
 
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| GetLatestSendErrorResult
 
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|-
 
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| 0x0013....
 
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| [[2.0.0-2]]
 
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| GetConnectionStatus
 
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|-
 
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| 0x0014....
 
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| [[2.0.0-2]]
 
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| GetTryingToConnectStatus
 
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|-
 
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| 0x0015....
 
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| [[2.0.0-2]]
 
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| GetReceiveSizeFreeAndUsed
 
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|-
 
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| 0x0016....
 
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| [[2.0.0-2]]
 
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| GetSendSizeFreeAndUsed
 
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|-
 
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| 0x0017....
 
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| [[2.2.0-X]]
 
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| GetConnectionRole
 
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|-
 
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| 0x00180182
 
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| [[2.2.0-X]]
 
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| InitializeIrnopShared (u32, u32, u32, u32, u32, u8, 0, handle)
 
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|-
 
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| 0x00190040
 
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| [[2.2.0-X]]
 
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| ReleaseReceivedData (32bit_value input)
 
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|-
 
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| 0x001A0040
 
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| [[2.2.0-X]]
 
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| SetOwnMachineId (u8 input)
 
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|}
 
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= Protocol description =
 
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Packets are sent using IrDA-SIR, with a 8N1 encoding (eight data bits, one stop bit, without parity). Each one is formed by a 2-byte header, a varint with the payload size, an obfuscated payload, and trailing error detection byte.
 
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== Packet header ==
 
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The packet header is fixed and consists in a synchronization byte (0xA5), followed by a unused (possibly RFU) zero byte. After these two hardcoded bytes, there's a varint representing the payload size, which may use one byte or two, depending on the how big the payload is.
 
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* For payloads with less than 64 bytes, the third byte represents the payload size.
 
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* For packets with up to 16383 bytes, the size is split in two bytes, with the third byte being the upper 6 bits of the payload size, OR'd with 0x40, and the fourth being the lower eight bits of the payload size
 
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For packets with less than 64 bytes:
 
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{| class="wikitable" border="1"
 
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! Sync
 
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! RFU
 
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! Size
 
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|-
 
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| 0xA5
 
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| 0x00
 
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| size
 
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|}
 
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For packets with up to 16383 bytes:
 
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{| class="wikitable" border="1"
 
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! Sync
 
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! RFU
 
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! Size (1)
 
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! Size (2)
 
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|-
 
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| 0xA5
 
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| 0x00
 
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| (size >> 8) <nowiki>|</nowiki> 0x40
 
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| size & 0xFF
 
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|}
 
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In C:
 
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<nowiki>uint8_t * setPacketHeader(uint8_t * buffer, size_t payloadSize) {
 
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assert(payloadSize < 16384);
 
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buffer[0] = 0xA5;
 
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buffer[1] = 0x00;
 
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if (payloadSize < 64) {
 
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buffer[2] = payloadSize;
 
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buffer += 3;
 
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} else {
 
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buffer[2] = 0x40 | (payloadSize >> 8);
 
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buffer[3] = payloadSize;
 
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buffer += 4;
 
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}
 
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return buffer;
 
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}</nowiki>
 
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== Payload ==
 
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The payload is obfuscated using a XOR-based encryption. In C:
 
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<nowiki>void payloadObfuscate(const void * voidplain, void * voidcipher, size_t size) {
 
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uint16_t * plain = (uint16_t *) voidplain;
 
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uint16_t * cipher = (uint16_t *) voidcipher;
 
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size_t halfCount = size / sizeof(uint16_t);
 
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uint16_t xorval = htobe16(0xE963);
 
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size_t i;
 
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for (i = 0; i < halfCount; i++) {
 
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xorval ^= plain[i];
 
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cipher[i] = xorval;
 
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}
 
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}
 
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void payloadDeobfuscate(const void * voidcipher, void * voidplain, size_t size) {
 
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uint16_t * cipher = (uint16_t *) voidcipher;
 
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uint16_t * plain = (uint16_t *) voidplain;
 
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size_t halfCount = size / sizeof(uint16_t);
 
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if (halfCount) {
 
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size_t i;
 
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for (i = halfCount - 1; i > 0; i--) {
 
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plain[i] = cipher[i] ^ cipher[i - 1];
 
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}
 
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plain[0] = cipher[0] ^ htobe16(0xE963);
 
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}
 
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}</nowiki>
 
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== Error detection ==
 
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The trailing error detection byte is calculated using [[CRC-8-CCITT]] <b>over the whole packet</b> (both the header and the payload)
 

Revision as of 15:21, 17 April 2015

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