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stmhal: Allow SPI.init to specify prescaler directly; improve SPI docs.

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This commit is contained in:
Damien George 2014-12-08 21:34:07 +00:00
parent 008251180d
commit b66a31c42c
2 changed files with 44 additions and 22 deletions
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19
docs/library/pyb.SPI.rst
View File

@ -52,12 +52,29 @@ Methods
Turn off the SPI bus.
.. method:: spi.init(mode, baudrate=328125, \*, polarity=1, phase=0, bits=8, firstbit=SPI.MSB, ti=False, crc=None)
.. method:: spi.init(mode, baudrate=328125, \*, prescaler, polarity=1, phase=0, bits=8, firstbit=SPI.MSB, ti=False, crc=None)
Initialise the SPI bus with the given parameters:
- ``mode`` must be either ``SPI.MASTER`` or ``SPI.SLAVE``.
- ``baudrate`` is the SCK clock rate (only sensible for a master).
- ``prescaler`` is the prescaler to use to derive SCK from the APB bus frequency;
use of ``prescaler`` overrides ``baudrate``.
- ``polarity`` can be 0 or 1, and is the level the idle clock line sits at.
- ``phase`` can be 0 or 1 to sample data on the first or second clock edge
respectively.
- ``firstbit`` can be ``SPI.MSB`` or ``SPI.LSB``.
- ``crc`` can be None for no CRC, or a polynomial specifier.
Note that the SPI clock frequency will not always be the requested baudrate.
The hardware only supports baudrates that are the APB bus frequency
(see :meth:`pyb.freq`) divided by a prescaler, which can be 2, 4, 8, 16, 32,
64, 128 or 256. SPI(1) is on AHB2, and SPI(2) is on AHB1. For precise
control over the SPI clock frequency, specify ``prescaler`` instead of
``baudrate``.
Printing the SPI object will show you the computed baudrate and the chosen
prescaler.
.. method:: spi.recv(recv, \*, timeout=5000)

47
stmhal/spi.c
View File

@ -346,8 +346,9 @@ STATIC void pyb_spi_print(void (*print)(void *env, const char *fmt, ...), void *
// SPI2 and SPI3 are on APB1
spi_clock = HAL_RCC_GetPCLK1Freq();
}
uint baudrate = spi_clock >> ((self->spi->Init.BaudRatePrescaler >> 3) + 1);
print(env, "SPI(%u, SPI.MASTER, baudrate=%u", spi_num, baudrate);
uint log_prescaler = (self->spi->Init.BaudRatePrescaler >> 3) + 1;
uint baudrate = spi_clock >> log_prescaler;
print(env, "SPI(%u, SPI.MASTER, baudrate=%u, prescaler=%u", spi_num, baudrate, 1 << log_prescaler);
} else {
print(env, "SPI(%u, SPI.SLAVE", spi_num);
}
@ -369,6 +370,7 @@ STATIC mp_obj_t pyb_spi_init_helper(const pyb_spi_obj_t *self, mp_uint_t n_args,
static const mp_arg_t allowed_args[] = {
{ MP_QSTR_mode, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 0} },
{ MP_QSTR_baudrate, MP_ARG_INT, {.u_int = 328125} },
{ MP_QSTR_prescaler, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0xffffffff} },
{ MP_QSTR_polarity, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 1} },
{ MP_QSTR_phase, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0} },
{ MP_QSTR_dir, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = SPI_DIRECTION_2LINES} },
@ -387,17 +389,20 @@ STATIC mp_obj_t pyb_spi_init_helper(const pyb_spi_obj_t *self, mp_uint_t n_args,
SPI_InitTypeDef *init = &self->spi->Init;
init->Mode = args[0].u_int;
// compute the baudrate prescaler from the requested baudrate
// select a prescaler that yields at most the requested baudrate
uint spi_clock;
if (self->spi->Instance == SPI1) {
// SPI1 is on APB2
spi_clock = HAL_RCC_GetPCLK2Freq();
} else {
// SPI2 and SPI3 are on APB1
spi_clock = HAL_RCC_GetPCLK1Freq();
// configure the prescaler
mp_uint_t br_prescale = args[2].u_int;
if (br_prescale == 0xffffffff) {
// prescaler not given, so select one that yields at most the requested baudrate
mp_uint_t spi_clock;
if (self->spi->Instance == SPI1) {
// SPI1 is on APB2
spi_clock = HAL_RCC_GetPCLK2Freq();
} else {
// SPI2 and SPI3 are on APB1
spi_clock = HAL_RCC_GetPCLK1Freq();
}
br_prescale = spi_clock / args[1].u_int;
}
uint br_prescale = spi_clock / args[1].u_int;
if (br_prescale <= 2) { init->BaudRatePrescaler = SPI_BAUDRATEPRESCALER_2; }
else if (br_prescale <= 4) { init->BaudRatePrescaler = SPI_BAUDRATEPRESCALER_4; }
else if (br_prescale <= 8) { init->BaudRatePrescaler = SPI_BAUDRATEPRESCALER_8; }
@ -407,19 +412,19 @@ STATIC mp_obj_t pyb_spi_init_helper(const pyb_spi_obj_t *self, mp_uint_t n_args,
else if (br_prescale <= 128) { init->BaudRatePrescaler = SPI_BAUDRATEPRESCALER_128; }
else { init->BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256; }
init->CLKPolarity = args[2].u_int == 0 ? SPI_POLARITY_LOW : SPI_POLARITY_HIGH;
init->CLKPhase = args[3].u_int == 0 ? SPI_PHASE_1EDGE : SPI_PHASE_2EDGE;
init->Direction = args[4].u_int;
init->DataSize = (args[5].u_int == 16) ? SPI_DATASIZE_16BIT : SPI_DATASIZE_8BIT;
init->NSS = args[6].u_int;
init->FirstBit = args[7].u_int;
init->TIMode = args[8].u_bool ? SPI_TIMODE_ENABLED : SPI_TIMODE_DISABLED;
if (args[9].u_obj == mp_const_none) {
init->CLKPolarity = args[3].u_int == 0 ? SPI_POLARITY_LOW : SPI_POLARITY_HIGH;
init->CLKPhase = args[4].u_int == 0 ? SPI_PHASE_1EDGE : SPI_PHASE_2EDGE;
init->Direction = args[5].u_int;
init->DataSize = (args[6].u_int == 16) ? SPI_DATASIZE_16BIT : SPI_DATASIZE_8BIT;
init->NSS = args[7].u_int;
init->FirstBit = args[8].u_int;
init->TIMode = args[9].u_bool ? SPI_TIMODE_ENABLED : SPI_TIMODE_DISABLED;
if (args[10].u_obj == mp_const_none) {
init->CRCCalculation = SPI_CRCCALCULATION_DISABLED;
init->CRCPolynomial = 0;
} else {
init->CRCCalculation = SPI_CRCCALCULATION_ENABLED;
init->CRCPolynomial = mp_obj_get_int(args[9].u_obj);
init->CRCPolynomial = mp_obj_get_int(args[10].u_obj);
}
// init the SPI bus