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, two signals called 'Nodestatus' and 'CPU-Load' will be sent in a CAN Message called 'Status' and updated through a CAN Message called 'Command' with the following Signal and Message definitions:
Signal Configuration
The Message Configuration below uses CAN Signals. Before CAN Messages can be used, each CAN signal must be configured accordingly. The Signal Configuration can be found in can_cfg.c. However, the "Signal Enumerations" are typically found in can_cfg.h. Signals allow the user to not worry about where a given signal is found within a CAN Message 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
};
1] Enumeration is used to simpilfy CAN Signal definitions and to ensure a consistent Message-to-Signal mapping.
2] CAN Signal configuration is done as a global constant to save RAM space and get a write-protected configuration. Also, the configuration data will be read while using the CAN Signal Layer.
3] The following will explain the required configuration for each Signal.
A] States the Initial Status of each signal.
B] States the width in bytes of the CAN signal. The Value here affects the Message Configuration's DLC & Number of Link parameters.
C] States the Initial Value for Each signal.
D] The Callback Function definition can be omitted by configuring the CANSIG_CALLBACK_EN parameter to 0 in can_cfg.h
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 */
}
}
};