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sam0/spi: Don't re-configure SPI device when not needed

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Currently, spi_acquire() will always re-configure the SPI bus.
If the configuration did not change, this is entirely uneccecary
and makes SPI operations take longer than needed.

Instead, compare the current configuration with the new configuration
and skip the initialisation if it didn't change since the last call.
This commit is contained in:
Benjamin Valentin 2019-10-08 13:58:54 +02:00 committed by Benjamin Valentin
parent a78bdaa85a
commit d21dc25cfe
1 changed files with 24 additions and 13 deletions
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37
cpu/sam0_common/periph/spi.c
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@ -104,29 +104,40 @@ void spi_init_pins(spi_t bus)
int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
{
(void) cs;
/* get exclusive access to the device */
mutex_lock(&locks[bus]);
/* power on the device */
poweron(bus);
/* disable the device */
dev(bus)->CTRLA.reg &= ~(SERCOM_SPI_CTRLA_ENABLE);
while (dev(bus)->SYNCBUSY.reg & SERCOM_SPI_SYNCBUSY_ENABLE) {}
/* configure bus clock, in synchronous mode its calculated from
* BAUD.reg = (f_ref / (2 * f_bus) - 1)
* with f_ref := CLOCK_CORECLOCK as defined by the board */
dev(bus)->BAUD.reg = (uint8_t)(((uint32_t)CLOCK_CORECLOCK) / (2 * clk) - 1);
const uint8_t baud = (((uint32_t)CLOCK_CORECLOCK) / (2 * clk) - 1);
/* configure device to be master and set mode and pads,
*
* NOTE: we could configure the pads already during spi_init, but for
* efficiency reason we do that here, so we can do all in one single write
* to the CTRLA register */
dev(bus)->CTRLA.reg = (SERCOM_SPI_CTRLA_MODE(0x3) | /* 0x3 -> master */
SERCOM_SPI_CTRLA_DOPO(spi_config[bus].mosi_pad) |
SERCOM_SPI_CTRLA_DIPO(spi_config[bus].miso_pad) |
(mode << SERCOM_SPI_CTRLA_CPHA_Pos));
const uint32_t ctrla = SERCOM_SPI_CTRLA_MODE(0x3) /* 0x3 -> master */
| SERCOM_SPI_CTRLA_DOPO(spi_config[bus].mosi_pad)
| SERCOM_SPI_CTRLA_DIPO(spi_config[bus].miso_pad)
| (mode << SERCOM_SPI_CTRLA_CPHA_Pos);
/* get exclusive access to the device */
mutex_lock(&locks[bus]);
/* power on the device */
poweron(bus);
/* configuration did not change */
if (dev(bus)->BAUD.reg == baud && dev(bus)->CTRLA.reg == ctrla) {
return SPI_OK;
}
/* disable the device */
dev(bus)->CTRLA.reg &= ~(SERCOM_SPI_CTRLA_ENABLE);
while (dev(bus)->SYNCBUSY.reg & SERCOM_SPI_SYNCBUSY_ENABLE) {}
dev(bus)->BAUD.reg = baud;
dev(bus)->CTRLA.reg = ctrla;
/* also no synchronization needed here, as CTRLA is write-synchronized */
/* finally enable the device */