Difference between revisions of "NFC adapter"

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−
The Nintendo NFC adapter is an upcoming external device which adds NFC capabilities for [[amiibo]]s to old Nintendo 3DS and Nintendo 2DS consoles, using the infrared port on the back of the console.
+
The Nintendo NFC adapter, formally '''Nintendo NFC Reader/Writer'''  and codenamed '''Fangate''', is an external device which adds NFC capabilities for [[amiibo]]s to old Nintendo 3DS and Nintendo 2DS consoles, using the infrared port on the back of the console.
 +
 
 +
It launched simultaneously with Animal Crossing Happy Home Designer, with which it's optionally bundled; it can also be bought standalone at a nominal price of 21 €.
  
 
[[File:150217nfcreader-640x360.jpg|thumb|right|250px|Media preview, as released by Nintendo]]
 
[[File:150217nfcreader-640x360.jpg|thumb|right|250px|Media preview, as released by Nintendo]]
Line 7: Line 9:
 
Based on analysis of the [[fangate_updater.bin]] file, which is part of the old Nintendo 3DS operating system since [[9.3.0-21]] and contains the firmware running on the external adapter; and analysis of the [[NFC Services]] running on old 3DS.
 
Based on analysis of the [[fangate_updater.bin]] file, which is part of the old Nintendo 3DS operating system since [[9.3.0-21]] and contains the firmware running on the external adapter; and analysis of the [[NFC Services]] running on old 3DS.
  
−
* SOC inside the adapter: Broadcom BCM20791B1
+
* SOC inside the adapter: Broadcom BCM20791B1 or ST proprietary "MCU-FGT/rev.A/GH24S VQ"
 
* CPU: ARM Cortex M0
 
* CPU: ARM Cortex M0
 
* Communications: infrared, with [[ir:USER]] running on the console. Uses obfuscated payloads. Baud rate is 115200 bps.
 
* Communications: infrared, with [[ir:USER]] running on the console. Uses obfuscated payloads. Baud rate is 115200 bps.
Line 38: Line 40:
 
Packets are sent using IrDA-SIR (using [[ir:USER]]), 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.
 
Packets are sent using IrDA-SIR (using [[ir:USER]]), 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.
  
−
== Packet header ==
+
== Layer 1 - framing format ==
−
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.
+
Frames are encoded using two different yet very simmilar formats, depending on how large the payload to be transmitted is:
−
 
 
 
* For payloads with less than 64 bytes, the third byte represents the payload size.
 
* For payloads with less than 64 bytes, the third byte represents the payload size.
 
* 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
 
* 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
  
−
For packets with less than 64 bytes:
+
{| class="wikitable" style="margin: 0 auto; text-align: center;"
−
{| class="wikitable" border="1"
+
|+IR framing format - short frame
−
! Sync
+
|-
−
! RFU
+
! style="border-top: none" | Byte
−
! Size
+
! style="width:10%;"| 7
 +
! style="width:10%;"| 6
 +
! style="width:10%;"| 5
 +
! style="width:10%;"| 4
 +
! style="width:10%;"| 3
 +
! style="width:10%;"| 2
 +
! style="width:10%;"| 1
 +
! style="width:10%;"| 0
 +
|-
 +
! 0x00
 +
| colspan="8"|Synchronization byte (<code>0xA5</code>)
 +
|-
 +
! 0x01
 +
| colspan="8"|Reserved for future use (<code>0x00</code>)
 +
|-
 +
! 0x02
 +
| RFU (<code>0</code>)
 +
| Short frame (<code>0</code>)
 +
| colspan="6"|Payload size
 +
|-
 +
! 0x03
 +
| colspan="8"|Payload byte 0
 +
|-
 +
| colspan="9"|...
 +
|-
 +
! 0x03+n-1
 +
| colspan="8"|Payload byte n-1
 
|-
 
|-
−
| 0xA5
+
! 0x03+n
−
| 0x00
+
| colspan="8"|[[CRC-8-CCITT]] computer over whole packet
−
| size
 
 
|}
 
|}
  
−
For packets with up to 16383 bytes:
+
 
−
{| class="wikitable" border="1"
+
{| class="wikitable" style="margin: 0 auto; text-align: center;"
−
! Sync
+
|+IR framing format - long frame
−
! RFU
 
−
! Size (1)
 
−
! Size (2)
 
 
|-
 
|-
−
| 0xA5
+
! style="border-top: none" | Byte
−
| 0x00
+
! style="width:10%;"| 7
−
| (size >> 8) <nowiki>|</nowiki> 0x40
+
! style="width:10%;"| 6
−
| size & 0xFF
+
! style="width:10%;"| 5
 +
! style="width:10%;"| 4
 +
! style="width:10%;"| 3
 +
! style="width:10%;"| 2
 +
! style="width:10%;"| 1
 +
! style="width:10%;"| 0
 +
|-
 +
! 0x00
 +
| colspan="8"|Synchronization byte: <code>0xA5</code>
 +
|-
 +
! 0x01
 +
| colspan="8"|Reserved for future use
 +
|-
 +
! 0x02
 +
| RFU (<code>0</code>)
 +
| Long frame (<code>1</code>)
 +
| colspan="6"|Payload size (upper 6 bits)
 +
|-
 +
! 0x03
 +
| colspan="8"|Payload size (lower 8 bits)
 +
|-
 +
! 0x04
 +
| colspan="8"|Payload byte 0
 +
|-
 +
| colspan="9"|...
 +
|-
 +
! 0x04+n-1
 +
| colspan="8"|Payload byte n-1
 +
|-
 +
! 0x04+n
 +
| colspan="8"|[[CRC-8-CCITT]] computer over whole packet
 
|}
 
|}
 +
 +
=== Header ===
 +
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.
  
 
In C:
 
In C:
Line 87: Line 143:
 
}</nowiki>
 
}</nowiki>
  
−
== Payload ==
+
=== Payload ===
 
The payload is obfuscated using a XOR-based encryption. In C:
 
The payload is obfuscated using a XOR-based encryption. In C:
 
  <nowiki>void payloadObfuscate(const void * voidplain, void * voidcipher, size_t size) {
 
  <nowiki>void payloadObfuscate(const void * voidplain, void * voidcipher, size_t size) {
 
uint16_t * plain = (uint16_t *) voidplain;
 
uint16_t * plain = (uint16_t *) voidplain;
 
uint16_t * cipher = (uint16_t *) voidcipher;
 
uint16_t * cipher = (uint16_t *) voidcipher;
−
size_t halfCount = size / sizeof(uint16_t);
+
size_t halfCount = size >> 1; // Divide by 2 rounding towards zero
  
 
uint16_t xorval = htobe16(0xE963);
 
uint16_t xorval = htobe16(0xE963);
Line 106: Line 162:
 
uint16_t * cipher = (uint16_t *) voidcipher;
 
uint16_t * cipher = (uint16_t *) voidcipher;
 
uint16_t * plain = (uint16_t *) voidplain;
 
uint16_t * plain = (uint16_t *) voidplain;
−
size_t halfCount = size / sizeof(uint16_t);
+
size_t halfCount = size >> 1; // Divide by 2 rounding towards zero
  
−
if (halfCount) {
+
uint16_t xorval = htobe16(0xE963);
−
size_t i;
+
size_t i;
−
for (i = halfCount - 1; i > 0; i--) {
 
−
plain[i] = cipher[i] ^ cipher[i - 1];
 
−
}
 
  
−
plain[0] = cipher[0] ^ htobe16(0xE963);
+
for (i = 0; i < halfCount; i++) {
 +
uint16_t word = plain[i];
 +
cipher[i] = xorval ^ word;
 +
xorval = word;
 
}
 
}
 
}</nowiki>
 
}</nowiki>
  
−
== Error detection ==
+
=== Error detection ===
 
The trailing error detection byte is calculated using [[CRC-8-CCITT]] <b>over the whole packet</b> (both the header and the payload)
 
The trailing error detection byte is calculated using [[CRC-8-CCITT]] <b>over the whole packet</b> (both the header and the payload)
 +
 +
== Layer 2 - "ircom" ==
 +
ircom is a simple stateful point-to-point master-slave communication protocol built on top of IR layer 1.
 +
 +
{| class="wikitable" style="margin: 0 auto; text-align: center;"
 +
! style="border-top: none" | Byte
 +
! style="width:10%;"| 7
 +
! style="width:10%;"| 6
 +
! style="width:10%;"| 5
 +
! style="width:10%;"| 4
 +
! style="width:10%;"| 3
 +
! style="width:10%;"| 2
 +
! style="width:10%;"| 1
 +
! style="width:10%;"| 0
 +
|-
 +
! 0x00
 +
| colspan="8"|Random value in range <code>0x01</code>~<code>0xFE</code>
 +
|-
 +
! 0x01
 +
| colspan="8"|Random value in range <code>0x01</code>~<code>0xFE</code>
 +
|-
 +
! 0x02
 +
| colspan="8"|Random value in range <code>0x01</code>~<code>0xFE</code>
 +
|-
 +
! 0x03
 +
| colspan="8"|Random value in range <code>0x01</code>~<code>0xFE</code>
 +
|-
 +
! 0x04
 +
| colspan="4"|RFU?
 +
| colspan="4"|Protocol version: <code>0x1</code>
 +
|-
 +
! 0x05
 +
| colspan="8"|Connection identifier
 +
|-
 +
! 0x06
 +
| colspan="8"|Reserved for future use?
 +
|-
 +
! 0x07
 +
| colspan="4"|???
 +
| colspan="4"|Operation code
 +
|-
 +
! 0x08+
 +
| colspan="8" style="background:#ffd0d0;"|Payload (if any)
 +
|}
 +
 +
* Random values are generated using a Mersenne Twister whose seed is based off the NFC adapter system tick counter. It is therefore random, and the 3DS won't attempt to validate them by any means. Its purpose is unknown.
 +
* NFC adapter will ignore packets whose protocol version is not 1. It will not even reply.
 +
* Connection identifier is a random byte the 3DS assigns to identify the connection should be several connections in range at once. Slave devices must save this value from the initial handshake packet and use it for replies. It must also ignore packets whose connection ID does not match.
 +
 +
=== Operation codes ===
 +
{| class="wikitable"
 +
! Code
 +
! Name
 +
! Has payload
 +
! Direction
 +
|-
 +
! 0x0
 +
| Layer 3 command?
 +
| style="background: green" | Yes
 +
| Master to slave
 +
|-
 +
! 0x1
 +
| ???
 +
| ???
 +
|-
 +
! 0x2
 +
| ???
 +
| ???
 +
|-
 +
! 0x3
 +
| ???
 +
| ???
 +
|-
 +
! 0x4
 +
| ???
 +
| ???
 +
|-
 +
! 0x5
 +
| ???
 +
| ???
 +
|-
 +
! 0x6
 +
| ???
 +
| ???
 +
|-
 +
! 0x7
 +
| ???
 +
| ???
 +
|-
 +
! 0x8
 +
| ???
 +
| ???
 +
|-
 +
! 0x9
 +
| ???
 +
| ???
 +
|-
 +
! 0xA
 +
| Disconnect request
 +
| style="background: red" | No
 +
| Master to slave
 +
|-
 +
! 0xB
 +
| Disconnection acknowledgment
 +
| style="background: red" | No
 +
| Slave to master
 +
|-
 +
! 0xC
 +
| Handshake
 +
| style="background: red" | No
 +
| Master to slave
 +
|-
 +
! 0xD
 +
| Handshake acknowledgement
 +
| style="background: red" | No
 +
| Slave to master
 +
|-
 +
! 0xE
 +
| ???
 +
| ???
 +
|-
 +
! 0xF
 +
| ???
 +
| ???
 +
|}
  
 
== Samples ==
 
== Samples ==
  
−
NFC adapter update beacon, as sent by the console:
+
NFC handshake beacons:
 
{| class="wikitable"
 
{| class="wikitable"
 
|-
 
|-
−
! Raw
+
! Layer 1 packet
−
! Deobfuscated
+
! Layer 2 packet
 +
! Layer 3 packet
 
|-
 
|-
 
| <code>A5 00 08 73 FE A5 C4 A4 2C A4 20 F5</code>
 
| <code>A5 00 08 73 FE A5 C4 A4 2C A4 20 F5</code>
 
| <code>9A 9D D6 3A 01 E8 00 0C</code>
 
| <code>9A 9D D6 3A 01 E8 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 D1 3E B7 7B B6 91 B6 9D 87</code>
 
| <code>A5 00 08 D1 3E B7 7B B6 91 B6 9D 87</code>
 
| <code>38 5D 66 45 01 EA 00 0C</code>
 
| <code>38 5D 66 45 01 EA 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 09 58 23 36 22 DA 22 D6 AE</code>
 
| <code>A5 00 08 09 58 23 36 22 DA 22 D6 AE</code>
 
| <code>E0 3B 2A 6E 01 EC 00 0C</code>
 
| <code>E0 3B 2A 6E 01 EC 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 5E DD A4 A0 A5 4E A5 42 A8</code>
 
| <code>A5 00 08 5E DD A4 A0 A5 4E A5 42 A8</code>
 
| <code>B7 BE FA 7D 01 EE 00 0C</code>
 
| <code>B7 BE FA 7D 01 EE 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 BC 19 C6 37 C7 C7 C7 CB 8B</code>
 
| <code>A5 00 08 BC 19 C6 37 C7 C7 C7 CB 8B</code>
 
| <code>55 7A 7A 2E 01 F0 00 0C</code>
 
| <code>55 7A 7A 2E 01 F0 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 C9 15 F6 63 F7 91 F7 9D B2</code>
 
| <code>A5 00 08 C9 15 F6 63 F7 91 F7 9D B2</code>
 
| <code>20 76 3F 76 01 F2 00 0C</code>
 
| <code>20 76 3F 76 01 F2 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 6E 48 47 1A 46 EE 46 E2 C7</code>
 
| <code>A5 00 08 6E 48 47 1A 46 EE 46 E2 C7</code>
 
| <code>87 2B 29 52 01 F4 00 0C</code>
 
| <code>87 2B 29 52 01 F4 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 A2 8C E5 C3 E4 35 E4 39 74</code>
 
| <code>A5 00 08 A2 8C E5 C3 E4 35 E4 39 74</code>
 
| <code>4B EF 47 4F 01 F6 00 0C</code>
 
| <code>4B EF 47 4F 01 F6 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 26 1C 07 10 06 E8 06 E4 64</code>
 
| <code>A5 00 08 26 1C 07 10 06 E8 06 E4 64</code>
 
| <code>CF 7F 21 0C 01 F8 00 0C</code>
 
| <code>CF 7F 21 0C 01 F8 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 7E 73 A2 3F A3 C5 A3 C9 FD</code>
 
| <code>A5 00 08 7E 73 A2 3F A3 C5 A3 C9 FD</code>
 
| <code>97 10 DC 4C 01 FA 00 0C</code>
 
| <code>97 10 DC 4C 01 FA 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 75 00 F3 B8 F2 44 F2 48 63</code>
 
| <code>A5 00 08 75 00 F3 B8 F2 44 F2 48 63</code>
 
| <code>9C 63 86 B8 01 FC 00 0C</code>
 
| <code>9C 63 86 B8 01 FC 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 8D AC 0F D5 0E 2B 0E 27 72</code>
 
| <code>A5 00 08 8D AC 0F D5 0E 2B 0E 27 72</code>
 
| <code>64 CF 82 79 01 FE 00 0C</code>
 
| <code>64 CF 82 79 01 FE 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 A3 55 7C 53 7D 52 7D 5E B2</code>
 
| <code>A5 00 08 A3 55 7C 53 7D 52 7D 5E B2</code>
 
| <code>4A 36 DF 06 01 01 00 0C</code>
 
| <code>4A 36 DF 06 01 01 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 15 06 43 C0 42 C3 42 CF 85</code>
 
| <code>A5 00 08 15 06 43 C0 42 C3 42 CF 85</code>
 
| <code>FC 65 56 C6 01 03 00 0C</code>
 
| <code>FC 65 56 C6 01 03 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 66 E0 9A 17 9B 12 9B 1E A0</code>
 
| <code>A5 00 08 66 E0 9A 17 9B 12 9B 1E A0</code>
 
| <code>8F 83 FC F7 01 05 00 0C</code>
 
| <code>8F 83 FC F7 01 05 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 A4 35 09 97 08 90 08 9C 25</code>
 
| <code>A5 00 08 A4 35 09 97 08 90 08 9C 25</code>
 
| <code>4D 56 AD A2 01 07 00 0C</code>
 
| <code>4D 56 AD A2 01 07 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 73 E2 BD AF BC A6 BC AA 60</code>
 
| <code>A5 00 08 73 E2 BD AF BC A6 BC AA 60</code>
 
| <code>9A 81 CE 4D 01 09 00 0C</code>
 
| <code>9A 81 CE 4D 01 09 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 02 57 D7 B0 D6 BB D6 B7 28</code>
 
| <code>A5 00 08 02 57 D7 B0 D6 BB D6 B7 28</code>
 
| <code>EB 34 D5 E7 01 0B 00 0C</code>
 
| <code>EB 34 D5 E7 01 0B 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 0D 79 01 AA 00 A7 00 AB 22</code>
 
| <code>A5 00 08 0D 79 01 AA 00 A7 00 AB 22</code>
 
| <code>E4 1A 0C D3 01 0D 00 0C</code>
 
| <code>E4 1A 0C D3 01 0D 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 14 91 04 B9 05 B6 05 BA B2</code>
 
| <code>A5 00 08 14 91 04 B9 05 B6 05 BA B2</code>
 
| <code>FD F2 10 28 01 0F 00 0C</code>
 
| <code>FD F2 10 28 01 0F 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 2C 86 B1 49 B0 58 B0 54 C0</code>
 
| <code>A5 00 08 2C 86 B1 49 B0 58 B0 54 C0</code>
 
| <code>C5 E5 9D CF 01 11 00 0C</code>
 
| <code>C5 E5 9D CF 01 11 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 D5 1D DE DB DF C8 DF C4 F9</code>
 
| <code>A5 00 08 D5 1D DE DB DF C8 DF C4 F9</code>
 
| <code>3C 7E 0B C6 01 13 00 0C</code>
 
| <code>3C 7E 0B C6 01 13 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 AF 75 DE 5C DF 49 DF 45 9C</code>
 
| <code>A5 00 08 AF 75 DE 5C DF 49 DF 45 9C</code>
 
| <code>46 16 71 29 01 15 00 0C</code>
 
| <code>46 16 71 29 01 15 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 C8 E2 5B C6 5A D1 5A DD B5</code>
 
| <code>A5 00 08 C8 E2 5B C6 5A D1 5A DD B5</code>
 
| <code>21 81 93 24 01 17 00 0C</code>
 
| <code>21 81 93 24 01 17 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 9B 51 68 2D 69 34 69 38 41</code>
 
| <code>A5 00 08 9B 51 68 2D 69 34 69 38 41</code>
 
| <code>72 32 F3 7C 01 19 00 0C</code>
 
| <code>72 32 F3 7C 01 19 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 13 7B 9F EF 9E F4 9E F8 32</code>
 
| <code>A5 00 08 13 7B 9F EF 9E F4 9E F8 32</code>
 
| <code>FA 18 8C 94 01 1B 00 0C</code>
 
| <code>FA 18 8C 94 01 1B 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 A7 62 02 9C 03 81 03 8D BD</code>
 
| <code>A5 00 08 A7 62 02 9C 03 81 03 8D BD</code>
 
| <code>4E 01 A5 FE 01 1D 00 0C</code>
 
| <code>4E 01 A5 FE 01 1D 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 39 06 94 36 95 29 95 25 09</code>
 
| <code>A5 00 08 39 06 94 36 95 29 95 25 09</code>
 
| <code>D0 65 AD 30 01 1F 00 0C</code>
 
| <code>D0 65 AD 30 01 1F 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 32 4C D7 C0 D6 E1 D6 ED 92</code>
 
| <code>A5 00 08 32 4C D7 C0 D6 E1 D6 ED 92</code>
 
| <code>DB 2F E5 8C 01 21 00 0C</code>
 
| <code>DB 2F E5 8C 01 21 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 83 BE F2 8F F3 AC F3 A0 B1</code>
 
| <code>A5 00 08 83 BE F2 8F F3 AC F3 A0 B1</code>
 
| <code>6A DD 71 31 01 23 00 0C</code>
 
| <code>6A DD 71 31 01 23 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 83 5E A0 57 A1 72 A1 7E F0</code>
 
| <code>A5 00 08 83 5E A0 57 A1 72 A1 7E F0</code>
 
| <code>6A 3D 23 09 01 25 00 0C</code>
 
| <code>6A 3D 23 09 01 25 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 6E C8 AD 69 AC 4E AC 42 D1</code>
 
| <code>A5 00 08 6E C8 AD 69 AC 4E AC 42 D1</code>
 
| <code>87 AB C3 A1 01 27 00 0C</code>
 
| <code>87 AB C3 A1 01 27 00 0C</code>
 +
| ␀
 
|-
 
|-
 
| <code>A5 00 08 C7 33 A1 2C A0 05 A0 09 FC</code>
 
| <code>A5 00 08 C7 33 A1 2C A0 05 A0 09 FC</code>
 
| <code>2E 50 66 1F 01 29 00 0C</code>
 
| <code>2E 50 66 1F 01 29 00 0C</code>
 +
| ␀
 
|}
 
|}
  
 
= External links =
 
= External links =
 
* [https://www.broadcom.com/products/NFC/NFC-Solutions/BCM2079x-Family BCM2079x brief on Broadcom's website]
 
* [https://www.broadcom.com/products/NFC/NFC-Solutions/BCM2079x-Family BCM2079x brief on Broadcom's website]

Revision as of 00:54, 30 April 2016

The Nintendo NFC adapter, formally Nintendo NFC Reader/Writer and codenamed Fangate, is an external device which adds NFC capabilities for amiibos to old Nintendo 3DS and Nintendo 2DS consoles, using the infrared port on the back of the console.

It launched simultaneously with Animal Crossing Happy Home Designer, with which it's optionally bundled; it can also be bought standalone at a nominal price of 21 €.

Media preview, as released by Nintendo


Technical details

Based on analysis of the fangate_updater.bin file, which is part of the old Nintendo 3DS operating system since 9.3.0-21 and contains the firmware running on the external adapter; and analysis of the NFC Services running on old 3DS.

  • SOC inside the adapter: Broadcom BCM20791B1 or ST proprietary "MCU-FGT/rev.A/GH24S VQ"
  • CPU: ARM Cortex M0
  • Communications: infrared, with ir:USER running on the console. Uses obfuscated payloads. Baud rate is 115200 bps.

Memory map:

Address Size Description
0x08008000 256KB? Firmware (fangate_updater.bin)
0x20000000 128KB? RAM
0x40023C00 0x1C FLASH ROM control
0xE000ED00 0x104 ARM Cortex system control block

IR communications

Packets are sent using IrDA-SIR (using ir:USER), 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.

Layer 1 - framing format

Frames are encoded using two different yet very simmilar formats, depending on how large the payload to be transmitted is:

  • For payloads with less than 64 bytes, the third byte represents the payload size.
  • 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
IR framing format - short frame
Byte 7 6 5 4 3 2 1 0
0x00 Synchronization byte (0xA5)
0x01 Reserved for future use (0x00)
0x02 RFU (0) Short frame (0) Payload size
0x03 Payload byte 0
...
0x03+n-1 Payload byte n-1
0x03+n CRC-8-CCITT computer over whole packet


IR framing format - long frame
Byte 7 6 5 4 3 2 1 0
0x00 Synchronization byte: 0xA5
0x01 Reserved for future use
0x02 RFU (0) Long frame (1) Payload size (upper 6 bits)
0x03 Payload size (lower 8 bits)
0x04 Payload byte 0
...
0x04+n-1 Payload byte n-1
0x04+n CRC-8-CCITT computer over whole packet

Header

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.

In C: 

uint8_t * setPacketHeader(uint8_t * buffer, size_t payloadSize) {
	assert(payloadSize < 16384);

	buffer[0] = 0xA5;
	buffer[1] = 0x00;

	if (payloadSize < 64) {
		buffer[2] = payloadSize;
		buffer += 3;
	} else {
		buffer[2] = 0x40 | (payloadSize >> 8);
		buffer[3] = payloadSize;
		buffer += 4;
	}

	return buffer;
}

Payload

The payload is obfuscated using a XOR-based encryption. In C: 

void payloadObfuscate(const void * voidplain, void * voidcipher, size_t size) {
	uint16_t * plain = (uint16_t *) voidplain;
	uint16_t * cipher = (uint16_t *) voidcipher;
	size_t halfCount = size >> 1; // Divide by 2 rounding towards zero

	uint16_t xorval = htobe16(0xE963);
	size_t i;

	for (i = 0; i < halfCount; i++) {
		xorval ^= plain[i];
		cipher[i] = xorval;
	}
}

void payloadDeobfuscate(const void * voidcipher, void * voidplain, size_t size) {
	uint16_t * cipher = (uint16_t *) voidcipher;
	uint16_t * plain = (uint16_t *) voidplain;
	size_t halfCount = size >> 1; // Divide by 2 rounding towards zero

	uint16_t xorval = htobe16(0xE963);
	size_t i;

	for (i = 0; i < halfCount; i++) {
		uint16_t word = plain[i];
		cipher[i] = xorval ^ word;
		xorval = word;
	}
}

Error detection

The trailing error detection byte is calculated using CRC-8-CCITT over the whole packet (both the header and the payload)

Layer 2 - "ircom"

ircom is a simple stateful point-to-point master-slave communication protocol built on top of IR layer 1.

Byte 7 6 5 4 3 2 1 0
0x00 Random value in range 0x01~0xFE
0x01 Random value in range 0x01~0xFE
0x02 Random value in range 0x01~0xFE
0x03 Random value in range 0x01~0xFE
0x04 RFU? Protocol version: 0x1
0x05 Connection identifier
0x06 Reserved for future use?
0x07 ??? Operation code
0x08+ Payload (if any)
  • Random values are generated using a Mersenne Twister whose seed is based off the NFC adapter system tick counter. It is therefore random, and the 3DS won't attempt to validate them by any means. Its purpose is unknown.
  • NFC adapter will ignore packets whose protocol version is not 1. It will not even reply.
  • Connection identifier is a random byte the 3DS assigns to identify the connection should be several connections in range at once. Slave devices must save this value from the initial handshake packet and use it for replies. It must also ignore packets whose connection ID does not match.

Operation codes

Code Name Has payload Direction
0x0 Layer 3 command? Yes Master to slave
0x1 ??? ???
0x2 ??? ???
0x3 ??? ???
0x4 ??? ???
0x5 ??? ???
0x6 ??? ???
0x7 ??? ???
0x8 ??? ???
0x9 ??? ???
0xA Disconnect request No Master to slave
0xB Disconnection acknowledgment No Slave to master
0xC Handshake No Master to slave
0xD Handshake acknowledgement No Slave to master
0xE ??? ???
0xF ??? ???

Samples

NFC handshake beacons:

Layer 1 packet Layer 2 packet Layer 3 packet
A5 00 08 73 FE A5 C4 A4 2C A4 20 F5 9A 9D D6 3A 01 E8 00 0C ␀
A5 00 08 D1 3E B7 7B B6 91 B6 9D 87 38 5D 66 45 01 EA 00 0C ␀
A5 00 08 09 58 23 36 22 DA 22 D6 AE E0 3B 2A 6E 01 EC 00 0C ␀
A5 00 08 5E DD A4 A0 A5 4E A5 42 A8 B7 BE FA 7D 01 EE 00 0C ␀
A5 00 08 BC 19 C6 37 C7 C7 C7 CB 8B 55 7A 7A 2E 01 F0 00 0C ␀
A5 00 08 C9 15 F6 63 F7 91 F7 9D B2 20 76 3F 76 01 F2 00 0C ␀
A5 00 08 6E 48 47 1A 46 EE 46 E2 C7 87 2B 29 52 01 F4 00 0C ␀
A5 00 08 A2 8C E5 C3 E4 35 E4 39 74 4B EF 47 4F 01 F6 00 0C ␀
A5 00 08 26 1C 07 10 06 E8 06 E4 64 CF 7F 21 0C 01 F8 00 0C ␀
A5 00 08 7E 73 A2 3F A3 C5 A3 C9 FD 97 10 DC 4C 01 FA 00 0C ␀
A5 00 08 75 00 F3 B8 F2 44 F2 48 63 9C 63 86 B8 01 FC 00 0C ␀
A5 00 08 8D AC 0F D5 0E 2B 0E 27 72 64 CF 82 79 01 FE 00 0C ␀
A5 00 08 A3 55 7C 53 7D 52 7D 5E B2 4A 36 DF 06 01 01 00 0C ␀
A5 00 08 15 06 43 C0 42 C3 42 CF 85 FC 65 56 C6 01 03 00 0C ␀
A5 00 08 66 E0 9A 17 9B 12 9B 1E A0 8F 83 FC F7 01 05 00 0C ␀
A5 00 08 A4 35 09 97 08 90 08 9C 25 4D 56 AD A2 01 07 00 0C ␀
A5 00 08 73 E2 BD AF BC A6 BC AA 60 9A 81 CE 4D 01 09 00 0C ␀
A5 00 08 02 57 D7 B0 D6 BB D6 B7 28 EB 34 D5 E7 01 0B 00 0C ␀
A5 00 08 0D 79 01 AA 00 A7 00 AB 22 E4 1A 0C D3 01 0D 00 0C ␀
A5 00 08 14 91 04 B9 05 B6 05 BA B2 FD F2 10 28 01 0F 00 0C ␀
A5 00 08 2C 86 B1 49 B0 58 B0 54 C0 C5 E5 9D CF 01 11 00 0C ␀
A5 00 08 D5 1D DE DB DF C8 DF C4 F9 3C 7E 0B C6 01 13 00 0C ␀
A5 00 08 AF 75 DE 5C DF 49 DF 45 9C 46 16 71 29 01 15 00 0C ␀
A5 00 08 C8 E2 5B C6 5A D1 5A DD B5 21 81 93 24 01 17 00 0C ␀
A5 00 08 9B 51 68 2D 69 34 69 38 41 72 32 F3 7C 01 19 00 0C ␀
A5 00 08 13 7B 9F EF 9E F4 9E F8 32 FA 18 8C 94 01 1B 00 0C ␀
A5 00 08 A7 62 02 9C 03 81 03 8D BD 4E 01 A5 FE 01 1D 00 0C ␀
A5 00 08 39 06 94 36 95 29 95 25 09 D0 65 AD 30 01 1F 00 0C ␀
A5 00 08 32 4C D7 C0 D6 E1 D6 ED 92 DB 2F E5 8C 01 21 00 0C ␀
A5 00 08 83 BE F2 8F F3 AC F3 A0 B1 6A DD 71 31 01 23 00 0C ␀
A5 00 08 83 5E A0 57 A1 72 A1 7E F0 6A 3D 23 09 01 25 00 0C ␀
A5 00 08 6E C8 AD 69 AC 4E AC 42 D1 87 AB C3 A1 01 27 00 0C ␀
A5 00 08 C7 33 A1 2C A0 05 A0 09 FC 2E 50 66 1F 01 29 00 0C ␀

External links

Retrieved from "https://www.3dbrew.org/w/index.php?title=NFC_adapter&oldid=17207"