This section will utilize previously mentioned CAN Signals, Messages, and Bus protocols and outline the 'Rx / Tx' example in can_demo.c.This demo will use multiple tasks to read, write, and update CAN Signals and Messages. It will also transmit messages and receive messages using the CAN Bus protocol. This section assumes that CAN Signals, Messages, and Bus configuration / initialization have already been done.
To select the 'Rx / Tx' example make sure that the following is set in can_demo.c:
/* CAN Demo Definitions. */
#define APP_CAN_RX_TX_DEMO 0u
#define APP_CAN_ECHO_DEMO 1u
/* --------------- uC/CAN DEMO SELECTION -------------- */
/* Select the CAN demo to run. */
#define APP_CAN_DEMO_SELECT APP_CAN_RX_TX_DEMO
The following demo is taken from the µCOS-II or -III can_demo.c file found in $:\Micrium\Software\uC-CAN\Examples. Please note that when running µC/CAN with NO OS the following demo will slightly vary. Please refer to the can_demo.c file for No OS ('NONE') for further details.
App_CAN_Startup()
void App_CAN_Startup (void)
{
CPU_INT16S can_err;
CANMSG_PARA *m;
#if (CANSIG_STATIC_CONFIG == 0u)
CANSIG_PARA *s;
#endif
#if ((APP_CAN_DEMO_SELECT == APP_CAN_RX_TX_DEMO) || \
(APP_CAN_DEMO_SELECT == APP_CAN_ECHO_DEMO))
CPU_INT08U os_err;
#endif
/* ------------------ HARDWARE SETUP ------------------ */
... [1]
/* ------------------- uC/CAN SETUP ------------------- */
CanSigInit(0L); [2] /* Initialize CAN Signals. */
#if (CANSIG_STATIC_CONFIG == 0u)
s = CanSig;
while (s < &CanSig[S_MAX]) { /* Create CAN Signals */
can_err = CanSigCreate(s);
if (can_err < 0) {
while (1); /* Failure Handling Here. */
}
s++;
}
#endif
CanMsgInit(0L); /* Initialize CAN Messages. */
m = (CANMSG_PARA *)CanMsg;
while (m < &CanMsg[CANMSG_N]) { /* Create CAN Messages. */
can_err = CanMsgCreate(m);
if (can_err < 0) {
while (1); /* Failure Handling Here. */
}
m++;
}
CanBusInit(0L); [3] /* Initialize CAN Objects & Bus Layer. */
can_err = CanBusEnable((CANBUS_PARA *)&CanCfg); /* Enable CAN Device according to Configuration. */
if (can_err != CAN_ERR_NONE) {
while (1); /* Failure Handling Here. */
}
/* ----------------- uC/OS DEMO TASKs ----------------- */
#if (APP_CAN_DEMO_SELECT == APP_CAN_RX_TX_DEMO)
... [4]
#endif
}
Rx_Task()
Once the Startup / Initialization of the CAN module is completed and without any errors, the Rx Task will Read the CAN Bus line and wait indefinitely (Set to blocking mode) until a CAN Frame with the appropriate Message ID arrives.
void Rx_Task (void *argp)
{
CANFRM frm;
CPU_INT16S msg;
CPU_INT08U busId;
(void)&argp; /* Suppress Compiler Warning. */
busId = 0u; /* CAN Device Number/ CAN Controller Number. */
CanBusIoCtl(busId, /* Rx Timeout is set to wait forever for a new Frame. */
CANBUS_SET_RX_TIMEOUT,
0);
while (DEF_ON) { /* Endless while loop. */
CanBusRead( busId, [1] /* Wait for new CAN Frame to Arrive. */
(void *)&frm,
sizeof(CANFRM));
msg = CanMsgOpen(busId, [2] /* Try to open the Received Frame on Message layer. */
frm.Identifier,
0);
if (msg >= 0) { /* If it could be opened, write the Frame on Msg layer. */
CanMsgWrite( msg, [3]
(void *)&frm,
sizeof(CANFRM));
}
}
}
Tx_Task() & Send_Status()
Concurrently, the Tx_Task will update a demo count variable and Transmit the CAN Signal it is configured to every 200ms. The transmission process will go as follows:
- Write CAN Signal -> Open CAN Message (with Tx Message ID) -> Read Message -> Write CAN Bus
void Tx_Task (void *argp)
{
(void)&argp; /* Suppress Compiler Warning. */
while (DEF_ON) { /* Endless while loop. */
DemoCnt++;
CanSigWrite( S_CPULOAD, /* Set an Incrementing Counter. */
&DemoCnt,
1);
if (DemoCnt >= DEF_OCTET_MASK) {
DemoCnt = 0u; /* Reset Demo Count to 0. */
}
Send_Status(); /* Send Signal Status on CAN bus */
OSTimeDlyHMSM(0u, 0u, 0u, 200u);
}
}
The communication protocol uses in most cases only the CAN messages. The application is responsible for the values of the mapped CAN signals. The following source code completes the example, started in chapter 6.4 Defining CAN Signals and Messages:
Source code (Protocol RX-Task)
This task could be started within Com_Start() to enable the receive activities as soon as the CAN bus is active.
Description
- Local variable to hold the received CAN frame.
- Local variable to hold the handle to message of received CAN identifier
- Set the RX timeout to 0 to enable the blocking mode, e.g. the function
CanBusRead()will wait forever for a CAN frame. - Wait for the next received CAN frame on CAN node 0.
- After reception, open the message with the received identifier.
- On success, write the received CAN frame to this message. This results in decomposing the CAN frame to all linked CAN signals.
Source code (Protocol Transmit Status)
This function can be called in your transmission task to transmit a specific CAN message, or called within a callback function to transmit information in response to a received CAN message.
Description
- Local variable to hold the CAN frame for transmission.
- Local variable to hold the handle to message which shall be transmitted
- Open the CAN message with the CAN-Identifier 0x150.
- On success, read the message to the local CAN frame. This results in collecting all linked signals and writing all information to the CAN frame at the defined locations.
- Send this constructed CAN frame via the CAN bus 0.