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stmhal: Improve CAN init so that it can take sjw, bs1, bs2 args.

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Also update docs to explain how CAN baudrate is determined.
This commit is contained in:
Damien George 2014-11-15 21:28:14 +00:00
parent 224fee0e10
commit d1b42d7b51
3 changed files with 32 additions and 12 deletions
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27
docs/library/pyb.CAN.rst
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@ -44,9 +44,32 @@ Methods
Initialise the CAN bus with the given parameters:
- ``mode`` is one of: NORMAL, LOOPBACK, SILENT, SILENT_LOOPBACK
- if ``extframe`` is True then the bus uses extended identifiers in the frames
(29 bits); otherwise it uses standard 11 bit identifiers
- ``prescaler`` is used to set the duration of 1 time quanta; the time quanta
will be the input clock (PCLK1, see :meth:`pyb.freq()`) divided by the prescaler
- ``sjw`` is the resynchronisation jump width in units of the time quanta;
it can be 1, 2, 3, 4
- ``bs1`` defines the location of the sample point in units of the time quanta;
it can be between 1 and 1024 inclusive
- ``bs2`` defines the location of the transmit point in units of the time quanta;
it can be between 1 and 16 inclusive
If ``extframe`` is True then the bus uses extended identifiers in the frames (29 bits).
Otherwise it uses standard 11 bit identifiers.
The time quanta tq is the basic unit of time for the CAN bus. tq is the CAN
prescaler value divided by PCLK1 (the frequency of internal peripheral bus 1);
see :meth:`pyb.freq()` to determine PCLK1.
A single bit is made up of the synchronisation segment, which is always 1 tq.
Then follows bit segment 1, then bit segment 2. The sample point is after bit
segment 1 finishes. The transmit point is after bit segment 2 finishes.
The baud rate will be 1/bittime, where the bittime is 1 + BS1 + BS2 multiplied
by the time quanta tq.
For example, with PCLK1=42MHz, prescaler=100, sjw=1, bs1=6, bs2=8, the value of
tq is 2.38 microseconds. The bittime is 35.7 microseconds, and the baudrate
is 28kHz.
See page 680 of the STM32F405 datasheet for more details.
.. method:: can.deinit()

14
stmhal/can.c
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@ -162,21 +162,15 @@ STATIC void pyb_can_print(void (*print)(void *env, const char *fmt, ...), void *
}
}
/// \method init(mode, extframe=False, prescaler=100, *, sjw=1, bs1=6, bs2=8)
///
/// Initialise the CAN bus with the given parameters:
///
/// - `mode` is one of: NORMAL, LOOPBACK, SILENT, SILENT_LOOPBACK
// init(mode, extframe=False, prescaler=100, *, sjw=1, bs1=6, bs2=8)
STATIC mp_obj_t pyb_can_init_helper(pyb_can_obj_t *self, mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
static const mp_arg_t allowed_args[] = {
{ MP_QSTR_mode, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = CAN_MODE_NORMAL} },
{ MP_QSTR_extframe, MP_ARG_BOOL, {.u_bool = false} },
{ MP_QSTR_prescaler, MP_ARG_INT, {.u_int = 100} },
/*
{ MP_QSTR_sjw, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 1} },
{ MP_QSTR_bs1, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 6} },
{ MP_QSTR_bs2, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 8} },
*/
};
// parse args
@ -190,9 +184,9 @@ STATIC mp_obj_t pyb_can_init_helper(pyb_can_obj_t *self, mp_uint_t n_args, const
CAN_InitTypeDef *init = &self->can.Init;
init->Mode = args[0].u_int << 4; // shift-left so modes fit in a small-int
init->Prescaler = args[2].u_int;
init->SJW = CAN_SJW_1TQ; // TODO set from args
init->BS1 = CAN_BS1_6TQ; // TODO set from args
init->BS2 = CAN_BS2_8TQ; // TODO set from args
init->SJW = ((args[3].u_int - 1) & 3) << 24;
init->BS1 = ((args[4].u_int - 1) & 0xf) << 16;
init->BS2 = ((args[5].u_int - 1) & 7) << 20;
init->TTCM = DISABLE;
init->ABOM = DISABLE;
init->AWUM = DISABLE;

3
stmhal/qstrdefsport.h
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@ -171,6 +171,9 @@ Q(addr)
Q(fifo)
Q(timeout)
Q(extframe)
Q(sjw)
Q(bs1)
Q(bs2)
Q(NORMAL)
Q(LOOPBACK)
Q(SILENT)