F280025 CAN internal clock

請問一下有範例程式是使用 internal clock 來驅動 CAN bus 嗎??

我想確定 CAN sysCLK 多少來設定 bandrate 。

#define DEVICE_SETCLOCK_CFG (SYSCTL_OSCSRC_OSC1 | SYSCTL_IMULT(40) | \
SYSCTL_REFDIV(2) | SYSCTL_ODIV(2) | \
SYSCTL_SYSDIV(1) | SYSCTL_PLL_ENABLE | \
SYSCTL_DCC_BASE_0)

現在我知道的是 intrnal clock 是10Mhz ，DEVICE_SETCLOCK_CFG 換算下來是  100 Mhz

但這是 CAN_sysCLK 嗎?  還是還要再做除頻的動作??

 另外我是不是還要使用這個功能  CAN_selectClockSource(uint32_t base, CAN_ClockSource source)，來確定設定他 internal clock。

但現在 CAN_setBitRate(CANA_BASE, DEVICE_SYSCLK_FREQ, 250000, 20);  裡面的 DEVICE_SYSCLK_FREQ  不清楚要設定多少??

Green Deng：

你好，例程C:\ti\c2000\C2000Ware_3_03_00_00\driverlib\f28002x\examples\can就是用的内部时钟。

然后，芯片TRM中有介绍：The CAN bit timing clock is normally derived from the system clock (SYSCLK)

例程中有介绍CAN_setBitRate

//*****************************************************************************
//
//! Sets the CAN Bit Timing based on requested Bit Rate.
//!
//! \param base is the base address of the CAN controller.
//! \param clock is the CAN module clock frequency before the bit rate
//!prescaler (Hertz)
//! \param bitRate is the desired bit rate (bits/sec)
//! \param bitTime is the number of time quanta per bit required for desired
//!bit time (Tq) and must be in the range from 8 to 25
//!
//! This function sets the CAN bit timing values for the bit rate passed in the
//! \e bitRate and \e bitTime parameters based on the \e clock parameter.The
//! CAN bit clock is calculated to be an average timing value that should work
//! for most systems.If tighter timing requirements are needed, then the
//! CAN_setBitTiming() function is available for full customization of all of
//! the CAN bit timing values.
//!
//! \note The CANBTR register values calculated by the function CAN_setBitRate
//!may not be suitable for your network parameters. If this is the case
//!and you have computed the correct values for your network, you could
//!directly write those parameters in CANBTR register using the
//!function CAN_setBitTiming.
//!
//! \return None.
//
//*****************************************************************************
extern void
CAN_setBitRate(uint32_t base, uint32_t clock, uint32_t bitRate,uint16_t bitTime);