How to increase SPI speed above 8 Mhz

[vn2000]

I'm trying to increase the SPI speed to drive a DAC that can go up to 50 Mhz. I'm using an nRF52840 DK and SDK V17.

Even if I can set up SPIM3, there is a limit I need to overcome in the firmware, which data rate is limited to 8 Mhz, in the follwing structure in nrf_drv_spi.h:

typedef enum
{
NRF_DRV_SPI_FREQ_125K = NRF_SPI_FREQ_125K, ///< 125 kbps.
NRF_DRV_SPI_FREQ_250K = NRF_SPI_FREQ_250K, ///< 250 kbps.
NRF_DRV_SPI_FREQ_500K = NRF_SPI_FREQ_500K, ///< 500 kbps.
NRF_DRV_SPI_FREQ_1M = NRF_SPI_FREQ_1M, ///< 1 Mbps.
NRF_DRV_SPI_FREQ_2M = NRF_SPI_FREQ_2M, ///< 2 Mbps.
NRF_DRV_SPI_FREQ_4M = NRF_SPI_FREQ_4M, ///< 4 Mbps.
NRF_DRV_SPI_FREQ_8M = NRF_SPI_FREQ_8M ///< 8 Mbps.
} nrf_drv_spi_frequency_t;

In the above typedef enum, I can't go above 8 Mhz. I'll be happy to go up to 32 Mhz or 48 Mhz.

[Nguyen Hoan Hoang]

These defines are found in the nrf52840_bitfields.h.  SPI freq for nrf52840 can go up to 32MHz

/* Bits 31..0 : SPI master data rate */

#define SPIM_FREQUENCY_FREQUENCY_Pos (0UL) /*!< Position of FREQUENCY field. */

#define SPIM_FREQUENCY_FREQUENCY_Msk (0xFFFFFFFFUL << SPIM_FREQUENCY_FREQUENCY_Pos) /*!< Bit mask of FREQUENCY field. */

#define SPIM_FREQUENCY_FREQUENCY_K125 (0x02000000UL) /*!< 125 kbps */

#define SPIM_FREQUENCY_FREQUENCY_K250 (0x04000000UL) /*!< 250 kbps */

#define SPIM_FREQUENCY_FREQUENCY_K500 (0x08000000UL) /*!< 500 kbps */

#define SPIM_FREQUENCY_FREQUENCY_M16 (0x0A000000UL) /*!< 16 Mbps */

#define SPIM_FREQUENCY_FREQUENCY_M1 (0x10000000UL) /*!< 1 Mbps */

#define SPIM_FREQUENCY_FREQUENCY_M32 (0x14000000UL) /*!< 32 Mbps */

#define SPIM_FREQUENCY_FREQUENCY_M2 (0x20000000UL) /*!< 2 Mbps */

#define SPIM_FREQUENCY_FREQUENCY_M4 (0x40000000UL) /*!< 4 Mbps */

#define SPIM_FREQUENCY_FREQUENCY_M8 (0x80000000UL) /*!< 8 Mbps */

[Hieu]

Hi vn2000,

What Hoang said is completely correct. I just want to add that you can also get a quick overview of the available peripherals and its maximum capabilities in the first page of the Product Specification, and more details in the dedicated peripheral page.

Hieu