Introduction
SIP-R stands for Serial Interface Protocol - Reliable
This is a protocol designed by Michael Richards and Marcell. It is designed specifically so tuning software can efficiently communicate with the ECU using a standard reliable protocol over serial bus (RS232 or RS485, or even CAN).
- It uses a pre-defined format that is easy to parse
- It provides forward and backward compatibility. (read: it does not restrict firmware developers by freezing a set of variable-offsets. Temporarily it's OK though).
- It is stateless and provides ack packets for every command sent. This allows continuous tasks like sensor logging to occur without interruption while setting and map adjustments are made.
- uses as much of existing standards as possible
- same human readable (nice to maintain, and there anyway) key=>binary offset translation as mcd (eg. config.cwl position=02). This is not necessary if the config offset database for the given config version is stored or cached in the tuningsoftare (not urgent).
- it supports some reasonable restrictions. Some table-data will be stored in EEPROM, so the firmware can only save one variable at a time. The tuningsoftware must support this (at least later, when needed): either by reading back variable, or rather the busy condition
- It's OK to send "empty" packets that only have flow control (NAK, or ACK), but normally, when there is "production talk", NAKs and ACKs must be piggybacked on production packets.
Entering SIPR mode
On startup the ECU can switch to the SIPR protocol by sending the command 'Mas'. You can only enter this from the MENU_ZERO state because this does not make sense for a keyboard user. Upon entering the protocol the string "OK\r\n" will be sent. This response was chosen for it's appearance while communicating interactively with a terminal program. If already in the SIPR mode the command 'Mas' can still be entered for the same result. This allows a more graceful recovery when communications are lost.
Packet Format
Every packet must be sent in the following format:
| Signature | Sequence | Type | Size | Data | CRC-16 |
| 1 byte | 1 byte | 1 byte | 1 byte | variable length of Size bytes | 2 bytes |
Discussion: The signature byte serves as a trigger to the receiver that a new packet is starting. 0x0A is defined as the byte to use. If the receiver gets a corrupted packet or times out receiving one it will return to a state where it is looking for a packet signature.
The sequence byte is necessary to ensure that ACK packets are matched with the command they refer to. If the tuning software sends 2 commands and one ACK becomes corrupted then the software must be able to correctly determine which command was accepted. In our case it is the responsibility of the sender to increment the sequence number with every command sent to ensure no collisions occur.
The type byte allows up to 255 different types of packets to be defined. In reality we expect to see about 30 different types. Should the need for more than 255 types ever arrive then an "extended" packet type could be defined by carrying extra type definition bytes into the data area.
There is only one byte designated for the data size. This means the largest possible packet will be 261 bytes - more than sufficient for the limited resources of the ECU. As apparent from the description above, size in this context refers only to the number of bytes in the data segment. In some packets it may also be valid to have 0 bytes of data.
Size number of bytes comprise the data segment or payload of a packet.
The last 2 bytes in a packet are the checksum bytes. CRC-16 was chosen because of it's proven track record and library availability. The CRC is applied to the entire packet excluding the signature byte and obviously the CRC bytes! The CRC low order byte is sent first.
Packet Type Definitions
NAK
- Sender: ECU
- Sequence: Set the same as the packet it is responding to.
- Type: 0x00
- Size: 0 (no data necessary)
- Response: none
- Description: The NAK packet is always sent in response to receiving an invalid (wrong CRC) or unrecognised (type not found) packet. In the future it may be necessary to add a reason byte to the data.
ACK
- Sender: ECU
- Sequence: Set the same as the packet it is responding to.
- Type: 0x01
- Size: 0 (no data necessary)
- Response: none
- Description: The ACK packet is always sent in response to a command packet. The ACK packet tells the sender that the command was received, understood and processed.
- Sender: Tuner
- Sequence: Sequentially chosen by the sender.
- Type: 0x01
- Size: 0 (no data necessary)
- Response: ACK
- Description: As a special case the tuning software can send an ACK and expect an ACK to be returned. This functions as a "Ping".
GET_VERSION
- Sender: Tuner
- Sequence: Sequentially chosen by the sender.
- Type: 0x02
- Size: 0 (no data necessary)
- Response: GET_VERSION
- Description: The GET_VERSION packet is sent by the tuning software to determine the version of firmware it is communicating with. This detail is often necessary to determine the features available to the software.
- Sender: ECU
- Sequence: Set the same as the packet it is responding to.
- Type: 0x02
- Size: 3
- Response: none
- Data: The 3 data bytes returned are the Major, Revision and Build numbers of the firmware. 0x01 0x00 0x03 for example would mean version 1.0.3
- Description: The GET_VERSION response packet provides the tuner with the firmware version.
SET_BAUD
- Sender: Tuner
- Sequence: Sequentially chosen by the sender.
- Type: 0x03
- Size: 1
- Response: ACK
- Data: The byte here represents the baudrate as chosen from the following table.
| byte | Baudrate |
| 0x00 | 9600 |
| 0x01 | 19200 (default rate) |
| 0x02 | 38400 |
| 0x03 | 57600 |
| 0x04 | 115200 |
- Description: The SET_BAUD command is a particular one. The ECU must respond in the current baudrate with it's ACK packet before switching baudrates. The tuning software must take care as missing the ACK packet may result in it retrying in the wrong baudrate. Once sent, the tuning software should wait for an ACK. Then resend. If it still does not receive an ACK then it should try switching to the new baudrate and sending one or more pings (ACK). Previously the data would have been the divisor needed to form the new baudrate. In the interest of portability I have chosen constants. In the future with an ARM processor the divisors may be different.
Does it make sense to use the same baudrate=1000000/x that is used at other places in the firmware? This covers every baudrate that is currently possible. The ARM would have no problem using (or converting from) these very same values. In any case, 0xE0..0xFF can be reserved for future (eg. other speeds, that don't fit this well). Otherwise we must be _very_ careful to choose the baudrates.
Besides me forgetting to list important baudrates these are very unlikely to change. I've seen these as the common baudrates for at least the past 15 years. I feel the using pre-defined values is clearer and less prone to errors. Being off by one for example will still work on many serial implementations but oddly not on others.
GET_TABLESIZE
- Sender: Tuner
- Sequence: Sequentially chosen by the sender.
- Type: 0x04
- Size: 1
- Response: GET_TABLESIZE
- Data: Only 1 data byte is sent to specify the table we are querying.
| byte | table |
| 0x01 | ignition table |
| 0x02 | lambda table |
| 0x03 | VE table |
- TODO: use the very same page addresses, and variable addresses within the page as used for MegaTune. See comm.c send_page() and store_page. Unfortunately we'll have to review addresses used by MegaTune (not very organized; maybe MegaTune addresses should change ?)
- Description: The GET_TABLESIZE packet is sent by the tuning software to determine the dimensions of a given table. Compiled options can alter the size of certain tables and knowing the correct sizes is very important.
- Sender: ECU
- Sequence: Set the same as the packet it is responding to.
- Type: 0x04
- Size: 2
- Response: none
- Data: the two data bytes correspond to the number of rows and columns respectively. a 5 row 2 column table would be sent as 0x05 0x02
- Description: The GET_TABLESIZE response tells the tuning software the dimensions of the specified table.
GET_TABLEDATA
- Sender: Tuner
- Sequence: Sequentially chosen by the sender.
- Type: 0x05
- Size: 1
- Response: GET_TABLEDATA
- Data: Only 1 data byte is sent to specify the table we are querying.
| byte | table |
| 0x01 | ignition table |
| 0x02 | labmda table |
| 0x03 | VE table |
- Description: The GET_TABLEDATA packet is sent by the tuning software to retrieve all the data from the specified table. GET_TABLESIZE can be called to determine the rows and columns format of this data.
.
- Sender: ECU
- Sequence: Set the same as the packet it is responding to.
- Type: 0x05
- Size: (determined by the actual size of the table)
- Response: none
- Data: The table data is returned as a byte stream.
- Description: The GET_TABLEDATA response sends the actual content of a table to the tuning software.
SET_TABLEDATA
- Sender: Tuner
- Sequence: Sequentially chosen by the sender.
- Type: 0x06
- Size: 3
- Response: ACK
- Data: The first data byte identifies the table we are modifying. The second byte contains the offset within that table and the third byte is the actual data.
| byte | table |
| 0x01 | ignition table |
| 0x02 | labmda table |
| 0x03 | VE table |
- Description: The SET_TABLEDATA packet is sent by the tuning software to modify an entry within a table. Ram constraints limit the size of the packet that can be sent to the ECU so modifications need to be performed one byte at a time.
READ_SENSORS
- Sender: Tuner
- Sequence: Sequentially chosen by the sender.
- Type: 0x07
- Size: 2
- Response: READ_SENSORS
- Data: The first data byte specifies the number of data sets to return. 0 means stop sending and 255 means send continuously.
The third byte selects the page number. Sensor data is paged as we don't always need all the info and for rapid datalogging this would just slow us down.
- Description: The READ_SENSORS packet is sent to request one or more sets of sensor data. The entire structure is returned in an effort to provide the maximum amount of data with a minimum amount of overhead. The repeat and delay bytes are very important for creating data logs as they allow the ECU to send the data at ECU determined intervals - more accurate and not subject to the stacking errors of the software generating the requests.
- Sender: ECU
- Sequence: Set the same as the packet it is responding to.
- Type: 0x07
- Size: varies according to the chosen page
- Response: none
- Data: Data format as specified in the following table
| offset | size | meaning |
| 0 | 1 | Packets remaining |
| 1 | 1 | Delay between packets (not sure on units yet) |
| 2+ | variable | sensor data |
Page0 Format
| offset | size | meaning |
| 2 | 2 | RPM |
| 4 | 2 | MAP value |
| 6 | 2 | inj pulsewidth |
| 8 | 2 | AFR1 |
| 10 | 2 | AFR2 |
| 12 | 1 | TPS value |
| 13 | 1 | CLT value |
| 14 | 1 | MAT value |
| 15 | 1 | battery voltage |
| 16 | 1 | ignition advance |
| 17 | 2 | EGT1 |
| 19 | 2 | EGT2 |
| 21 | 2 | target boost |
| 23 | 1 | boost duty cycle |
GET_HWSIG
- Sender: Tuner
- Sequence: Chosen by the sender.
- Type: 0x08
- Size: 0
- Response: HWSIG
- Data:
This packet requests the hardware signature bytes from the ECU. These are stored in the bootloader area and are not always available (only if the bootloader was uploaded properly: for every v3.x since v3.2).
- Sender: ECU
- Sequence: Set the same as the packet it is responding to.
- Type: 0x08
- Size: 12
- Response: none
- Data: Data format as specified in the following table
| offset | size | meaning |
| 0 | 1 | Signature byte (data valid when 0xAA |
| 1 | 1 | Board Revision Number |
| 2 | 1 | Reserved |
| 3 | 1 | Reserved |
| 4 | 1 | Hardware Options |
| 5 | 1 | Trigger Types |
| 6 | 1 | Reserved |
| 7 | 1 | Reserved |
| 8 | 1 | Reserved |
| 9 | 1 | Reserved |
| 10 | 1 | Reserved |
| 11 | 2 | Board serial number (16 bit) |
BEGIN_FLASH
- Sender: Tuner
- Sequence: Chosen by the sender.
- Type: 0x09
- Size: 0
- Response: NONE
This packet signals the ECU to enter bootloader mode. In order to do this the engine must be stopped. If this condition is not met then a NAK packet will be sent. It is up to the tuning software to determine this.
SerialComm/SIPR/Ideas - Other work and ideas not currently part of SIPR.