I am going through UG585 document and trying to understand the formulas for the can bus baud rate. I am using the example from SDK (xcanps_intr_example). I am trying to understand how they are arriving at those numbers. Ultimately I would like to set up the baud rate at 1 megabit per second.
/*
* The Baud Rate Prescaler Register (BRPR) and Bit Timing Register (BTR)
* are setup such that CAN baud rate equals 40Kbps, assuming that the
* the CAN clock is 24MHz. The user needs to modify these values based on
* the desired baud rate and the CAN clock frequency. For more information
* see the CAN 2.0A, CAN 2.0B, ISO 11898-1 specifications.
*/
/*
* Timing parameters to be set in the Bit Timing Register (BTR).
* These values are for a 40 Kbps baudrate assuming the CAN input clock
* frequency is 24 MHz.
*/
#define TEST_BTR_SYNCJUMPWIDTH 3
#define TEST_BTR_SECOND_TIMESEGMENT 2
#define TEST_BTR_FIRST_TIMESEGMENT 15
/*
* The Baud rate Prescalar value in the Baud Rate Prescaler Register
* needs to be set based on the input clock frequency to the CAN core and
* the desired CAN baud rate.
* This value is for a 40 Kbps baudrate assuming the CAN input clock frequency
* is 24 MHz.
*/
#define TEST_BRPR_BAUD_PRESCALAR 29
Formulas from the UG585:
tTQ_CLK = tCAN_REF_CLK * (can.BRPR[BRP] + 1)
freqTQ_CLK = freqCAN_REF_CLK / (can.BRPR[BRP] + 1)
tSYNC_SEGMENT = 1 * tTQ_CLK
tTIME_SEGMENT1 = tTQ_CLK * (can.BTR[TS1] + 1)
tTIME_SEGMENT2 = tTQ_CLK * (can.BTR[TS2] + 1)
tBIT_RATE = tSYNC_SEGMENT + tTIME_SEGMENT1 + tTIME_SEGMENT2
freqBIT_RATE = freqCAN_REF_CLK / ((can.BRPR[BRP] + 1) * (3 + can.BTR[TS1] + can.BTR[TS2]))
How are they deriving those numbers? How do I choose BRP? How are they getting TEST_BTR_SYNCJUMPWIDTH, TEST_BTR_SECOND_TIMESEGMENT and TEST_BTR_FIRST_TIMESEGMENT. Again I am trying to understand configure the baud rate for 1 megabit per second.
