Chapter 2. API Reference
not use this when there is still a transaction that hasn’t been finalized.
Note This function is not thread safe when multiple tasks access the same SPI device. Normally a device
cannot start (queue) polling and interrupt transactions simutanuously.
Return
• ESP_ERR_INVALID_ARG if parameter is invalid
• ESP_OK on success
Parameters
• handle: Device handle obtained using spi_host_add_dev
• trans_desc: Description of transaction to execute
esp_err_t spi_device_acquire_bus(spi_device_handle_t device, TickType_t wait)
Occupy the SPI bus for a device to do continuous transactions.
Transactions to all other devices will be put off until spi_device_release_bus is called.
Note The function will wait until all the existing transactions have been sent.
Return
• ESP_ERR_INVALID_ARG : wait is not set to portMAX_DELAY.
• ESP_OK : Success.
Parameters
• device: The device to occupy the bus.
• wait: Time to wait before the the bus is occupied by the device. Currently MUST set to port-
MAX_DELAY.
void spi_device_release_bus(spi_device_handle_t dev)
Release the SPI bus occupied by the device. All other devices can start sending transactions.
Parameters
• dev: The device to release the bus.
int spi_cal_clock(int fapb, int hz, int duty_cycle, uint32_t *reg_o)
Calculate the working frequency that is most close to desired frequency, and also the register value.
Parameters
• fapb: The frequency of apb clock, should be APB_CLK_FREQ.
• hz: Desired working frequency
• duty_cycle: Duty cycle of the spi clock
• reg_o: Output of value to be set in clock register, or NULL if not needed.
Return Actual working frequency that most fit.
int spi_get_actual_clock(int fapb, int hz, int duty_cycle)
Calculate the working frequency that is most close to desired frequency.
Return Actual working frequency that most fit.
Parameters
• fapb: The frequency of apb clock, should be APB_CLK_FREQ.
• hz: Desired working frequency
• duty_cycle: Duty cycle of the spi clock
void spi_get_timing(bool gpio_is_used, int input_delay_ns, int eff_clk, int *dummy_o, int
*cycles_remain_o)
Calculate the timing settings of specified frequency and settings.
Note If **dummy_o* is not zero, it means dummy bits should be applied in half duplex mode, and full duplex
mode may not work.
Parameters
• gpio_is_used: True if using GPIO matrix, or False if iomux pins are used.
• input_delay_ns: Input delay from SCLK launch edge to MISO data valid.
• eff_clk: Effective clock frequency (in Hz) from spi_cal_clock.
• dummy_o: Address of dummy bits used output. Set to NULL if not needed.
• cycles_remain_o: Address of cycles remaining (after dummy bits are used) output.
– -1 If too many cycles remaining, suggest to compensate half a clock.
– 0 If no remaining cycles or dummy bits are not used.
Espressif Systems 377
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