ESP32 Forum

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// Configuration for the SPI bus
	spi_bus_config_t buscfg = {
		.mosi_io_num = DATA_PIN,
		.miso_io_num = 5,
		.sclk_io_num = CLK_PIN,
		.quadwp_io_num = -1,
		.quadhd_io_num = -1,
		.max_transfer_sz = SPI_MAX_DMA_LEN,
	};

	// Configuration for the SPI master interface
	spi_device_interface_config_t devcfg = {
		.command_bits = 0,
		.address_bits = 0,
		.dummy_bits = 0,
		.duty_cycle_pos = 128,
		.cs_ena_pretrans = 0,
		.cs_ena_posttrans = 0,
		.clock_speed_hz = 26*1000*1000,
		.mode = 0,
		.spics_io_num = 17,
		.queue_size = 1,
		.flags = 0,
		.pre_cb = NULL,
		.post_cb = NULL,
	};
	
	// Initialize and enable SPI
	spi_bus_initialize(VSPI_HOST, &buscfg, 1);
	spi_bus_add_device(VSPI_HOST, &devcfg, &spi_handle);

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// Full buffer DMA transfer
int32_t spi_dma_transfer_bytes(uint8_t *data, uint16_t size) {
	esp_err_t trans_result = ESP_OK;
	spi_transaction_t trans_t;

	// Prepare transaction parameters
	trans_t.rx_buffer = NULL;
	trans_t.tx_buffer = data;
	trans_t.rxlength = 0;
	trans_t.length = 8 * size;
	trans_t.flags = 0;
	trans_t.cmd = 0;
	trans_t.addr = 0;
	trans_t.user = NULL;

	// Perform transaction
	trans_result = spi_device_transmit(spi_handle, &trans_t);
	if (ESP_OK != trans_result) {
		return -1;
	}

	return size;
}

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-Using polling, if you don't mind the CPU being busy while waiting, rather than go do something else.

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trans_result=spi_device_polling_transmit(spi_handle, &trans_t);