Posted on March 24, 2012 at 11:39Hi,
I'm having troubles setting up the CAN bus on my STM32F103R4. I'm using the can example from the keil homepage . When it is about to leave initialization mode, hardware doesnt reset the INAK bit in MSR register and I really don't know why.
Here's the relevant slice of the code:
void
CAN_setup (
void
) {
unsigned
int
brp = stm32_GetPCLK1(); RCC->APB1ENR |= RCC_APB1ENR_CANEN;
// enable clock for CAN
// Note: MCBSTM32 uses PB8 and PB9 for CAN
RCC->APB2ENR |= RCC_APB2ENR_AFIOEN;
// enable clock for Alternate Function
AFIO->MAPR &=
0xFFFF9FFF
;
// reset CAN remap
AFIO->MAPR |=
0x00004000
;
// set CAN remap, use PB8, PB9
RCC->APB2ENR |= RCC_APB2ENR_IOPBEN;
// enable clock for GPIO B
GPIOB->CRH &= ~(
0x0F
<<
0
); GPIOB->CRH |= (
0x08
<<
0
);
// CAN RX pin PB.8 input push pull
GPIOB->CRH &= ~(
0x0F
<<
4
); GPIOB->CRH |= (
0x0B
<<
4
);
// CAN TX pin PB.9 alternate output push pull
NVIC->ISER[
0
] |= (
1
<< (USB_HP_CAN_TX_IRQChannel &
0x1F
));
// enable interrupt
NVIC->ISER[
0
] |= (
1
<< (USB_LP_CAN_RX0_IRQChannel &
0x1F
));
// enable interrupt
CAN->MCR = (CAN_MCR_NART | CAN_MCR_INRQ);
// init mode, disable auto. retransmission
// Note: only FIFO 0, transmit mailbox 0 used
CAN->IER = (CAN_IER_FMPIE0 | CAN_IER_TMEIE);
// FIFO 0 msg pending, Transmit mbx empty
/* Note: this calculations fit for PCLK1 = 36MHz */
brp = (brp /
18
) /
500000
;
// baudrate is set to 500k bit/s
/* set BTR register so that sample point is at about 72% bit time from bit start */
/* TSEG1 = 12, TSEG2 = 5, SJW = 4 => 1 CAN bit = 18 TQ, sample at 72% */
CAN->BTR &= ~(((
0x03
) <<
24
) | ((
0x07
) <<
20
) | ((
0x0F
) <<
16
) | (
0x1FF
)); CAN->BTR |= ((((
4
-
1
) &
0x03
) <<
24
) | (((
5
-
1
) &
0x07
) <<
20
) | (((
12
-
1
) &
0x0F
) <<
16
) | ((brp-
1
) &
0x1FF
)); }
void
CAN_testmode (
unsigned
int
testmode) { CAN->BTR &= ~(CAN_BTR_SILM | CAN_BTR_LBKM);
// set testmode
CAN->BTR |= (testmode & (CAN_BTR_SILM | CAN_BTR_LBKM)); }
void
CAN_start (
void
) { CAN->MCR &= ~CAN_MCR_INRQ;
// normal operating mode, reset INRQ
while
(CAN->MSR & CAN_MCR_INRQ); } I hope somebody knows how to fix that!
Regards.
Alex
