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reformatting README

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Riccardo 2017-08-05 01:41:09 -07:00
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@ -19,31 +19,31 @@ Use [panda](https://github.com/commaai/panda) to connect your car to a computer.
### Good practices for contributing to opendbc ### Good practices for contributing to opendbc
- Comments: the best way to store comments is to add them directly to the DBC files. For example: - Comments: the best way to store comments is to add them directly to the DBC files. For example:
``` ```
CM_ SG_ 490 LONG_ACCEL "wheel speed derivative, noisy and zero snapping"; CM_ SG_ 490 LONG_ACCEL "wheel speed derivative, noisy and zero snapping";
``` ```
is a comment that refers to signal `LONG_ACCEL` in message `490`. Using comments is highly recommended, especially for doubts and uncertainties. [cabana](https://community.comma.ai/cabana/) can easily display/add/edit comments to signals and messages. is a comment that refers to signal `LONG_ACCEL` in message `490`. Using comments is highly recommended, especially for doubts and uncertainties. [cabana](https://community.comma.ai/cabana/) can easily display/add/edit comments to signals and messages.
- Units: when applicable, it's recommended to convert signals into physical units, by using a proper signal factor. Using a SI unit is preferred, unless a non-SI unit rounds the signal factor much better. - Units: when applicable, it's recommended to convert signals into physical units, by using a proper signal factor. Using a SI unit is preferred, unless a non-SI unit rounds the signal factor much better.
For example: For example:
``` ```
SG_ VEHICLE_SPEED : 7|15@0+ (0.00278,0) [0|70] "m/s" PCM SG_ VEHICLE_SPEED : 7|15@0+ (0.00278,0) [0|70] "m/s" PCM
``` ```
is better than: is better than:
``` ```
SG_ VEHICLE_SPEED : 7|15@0+ (0.00620,0) [0|70] "mph" PCM SG_ VEHICLE_SPEED : 7|15@0+ (0.00620,0) [0|70] "mph" PCM
``` ```
However, the cleanest option is really: However, the cleanest option is really:
``` ```
SG_ VEHICLE_SPEED : 7|15@0+ (0.01,0) [0|70] "kph" PCM SG_ VEHICLE_SPEED : 7|15@0+ (0.01,0) [0|70] "kph" PCM
``` ```
- Signal's size: always use the smallest amount of bits possible. For example, let's say I'm reverse engineering the gas pedal position and I've determined that it's in a 3 bytes message. For 0% pedal position I read a message value of `0x000000`, while for 100% of pedal position I read `0x640000`: clearly, the gas pedal position is within the first byte of the message and I might be tempted to define the signal `GAS_POS` as: - Signal's size: always use the smallest amount of bits possible. For example, let's say I'm reverse engineering the gas pedal position and I've determined that it's in a 3 bytes message. For 0% pedal position I read a message value of `0x000000`, while for 100% of pedal position I read `0x640000`: clearly, the gas pedal position is within the first byte of the message and I might be tempted to define the signal `GAS_POS` as:
``` ```
SG_ GAS_POS : 7|8@0+ (1,0) [0|100] "%" PCM SG_ GAS_POS : 7|8@0+ (1,0) [0|100] "%" PCM
``` ```
However, I can't be sure that the very first bit of the message is referred to the pedal position: I haven't seen it changing! Therefore, a safer way of defining the signal is: However, I can't be sure that the very first bit of the message is referred to the pedal position: I haven't seen it changing! Therefore, a safer way of defining the signal is:
``` ```
SG_ GAS_POS : 6|7@0+ (1,0) [0|100] "%" PCM SG_ GAS_POS : 6|7@0+ (1,0) [0|100] "%" PCM
``` ```
which leaves the first bit unallocated. This prevents from very erroneous reading of the gas pedal position, in case the first bit is indeed used for something else. which leaves the first bit unallocated. This prevents from very erroneous reading of the gas pedal position, in case the first bit is indeed used for something else.