AN2628

Programming through polling

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Programming through polling

Programming the interrupt driver using polling generates an interrupt whenever a successful

transmission or reception occurs. This is done by setting bit SIE of the control register.

RXOK or TXOK is (or both are) set when a message object transmits or receives a

message.

The CAN module sets RXOK whenever a message is acknowledged on the CAN bus.

Once in the interrupt routine, the CPU polls bit IntPnd of each message object. The

message object polling sequence defines the message object priority, independent of the

existing hardware priority scheme defined for IntId.

Polling is high in the CPU overhead as the CPU is interrupted every time a message is

acknowledged on the CAN bus. Therefore, programming the interrupt driver using polling is

recommended for small networks only.

This section provides a sample program for programming through polling.

// CAN interrupt driver

//

include <REGF2xxx.h> // standard include file for F27x/F25x

#include "CCAN_drvs.h" // inc file to define bit masks and macro

// see Section 6 for description.

interrupt(0x4x) // CAN Module IR, trap number 0x40, 0x41, 0x43,

void CAN_IT (void)// according to user choice see Section 1.1

{

unsigned short i;

unsigned char status, control;

{

status = CANxSR;// copy status + control REG to variable

control = CANxCR;

CANxSR=0; // clear status register

XIRxCLR = 0xXX; //flag to be cleared according to user choice

//see Section 1.1

CANxIF1CM = 0x7F;

// Transfer entire message into interface

CANxIF1CR = 1;

// register and clear IntPnd and NewDat

CANx_WAIT_FOR_IF1;

if (CANxIF1MC & IF_INTPND)

{.....} // procedure to handle message 1 interrupts

....

CANxIF1CM = 0x7F;

// Transfer entire message into inference

CANxIF1CR = 32;

// register and clear IntPnd and NewDat

CANx_WAIT_FOR_IF1;

if (CANxIF1MC & IF_INTPND)

{.....} // procedure to handle message 32 interrupts

}