To get a higher level of abstraction, CAN Signals and Messages can be used to abstract information mappings to the Bus communication objects. In this topic example, the information from the 'Nodestatus' and 'CPU-Load' will be sent in a CAN Frame called 'Status' and updated through a CAN Frame called 'Command' with the following definitions:
Signal Configuration
The Message Configuration below uses CAN Signals. Before CAN Messages can be used, each CAN signal must be configured accordingly. Signals allow the user to not worry about where a given signal if found within a CAN Frame, while containing different types of data. For more information about CAN Signals click Here.
Note:
- A CAN Signal can be defined without any CAN communication knowledge. No information about sending or receiving information is needed during configuration.
#include "can_sig.h"
enum { [1] /* ---------------- SIGNAL ENUMERATIONS --------------- */
S_NODESTATUS = 0,
S_CPULOAD,
S_MAX,
};
const CANSIG_PARA CanSig[CANSIG_N] = { [2]
/* ---------------- SIGNAL NODESTATUS ----------------- */
{CANSIG_UNCHANGED, [3A] /* Initial Status */
1, [B] /* Width in Bytes */
0, [C] /* Initial Value */
#if (CANSIG_CALLBACK_EN > 0)
StatusChange}, [D] /* Callback Function: User Defined */
#else
},
#endif
/* ----------------- SIGNAL CPULOAD ------------------- */
{CANSIG_UNCHANGED, [3A] /* Initial Status */
1, [B] /* Width in Bytes */
0, [C] /* Initial Value */
#if (CANSIG_CALLBACK_EN > 0)
0} [D] /* No Callback */
#else
},
#endif
};
Message Configuration
The Message Configuration can be found in can_cfg.c. However, the "Message Enumerations" are typically found in can_cfg.h. Please note that CAN Signals must be configured prior to be used in CAN Messages. For more information on CAN Messages click Here.
Note:
- A CAN Message can be defined without any knowledge of the information generated and/or the usage of the payload. Only the mapping of the payload (and it's respective parts) must be known.
#include "can_msg.h"
enum { [1] /* --------------- MESSAGE ENUMERATIONS --------------- */
M_STATUS = 0,
M_COMMAND,
M_MAX
};
const CANMSG_PARA CanMsg[CANMSG_N] = [2]
{
/* ------------------ MESSAGE STATUS ------------------ */
{ 0x123L, [3A] /* CAN-Identifier */
CANMSG_TX, [B] /* Message Type */
2, [C] /* DLC of Message */
2, /* No. of Links */
{ { S_NODESTATUS, [D] /* Signal ID */
0 }, [E] /* Byte Position */
{ S_CPULOAD, /* Signal ID */
2 } /* Byte Position */
},
},
/* ----------------- MESSAGE COMMAND ------------------ */
{ 0x122L, [4A] /* CAN-Identifier */
CANMSG_RX, [B] /* Message Type */
1, [C] /* DLC of Message */
1, /* No. of Links */
{ { S_NODESTATUS, [D] /* Signal ID */
0 } [E] /* Byte Position */
}
}
};
Example
The information Nodestatus and CPU-Load shall be sent in a CAN frame called Status with the following definition:
CAN-Identifier = 0x150
DLC = 2
Payload Byte 0 = Current Nodestatus
Payload Byte 1 = CPU-Load
The Nodestatus shall be settable via the CAN frame called Command with the following definition:
CAN-Identifier = 0x140
DLC = 1
Payload Byte 0 = New Nodestatus
If the information Nodestatus is changed, the following actions shall be done:
New Nodestatus = 1: Start the task Load-Task New Nodestatus = 2: Stop the task Load-Task
Source code (Part 1)
Additional Information
- The CAN signals can be defined without any CAN communication knowledge. No information about sending or receiving the information is needed during this state.
- The enumeration is used to simplify the message definition and ensure to get a consistent message to signal mapping.
- The CAN signal configuration is done as a global constant to safe RAM space and get a write protected configuration.
- This variable must be declared globally, because the configuration data will be read while using the CAN signal layer.
- The callback function definition may be omitted by configuring the
CANSIG_CALLBACK_ENparameter to 0.