SPI Introduction SPI is a high-speed, full-duplex, synchronous serial communication interface for connecting microcontroller, sensors, storage devices, etc. The Firefly-RK3399 development board provides the SPI1 (single chip optional) interface, and the specific position is as follows: How SPI works SPI works in a master-slave mode, which typically has one master device and one or more slave devices, requiring at least four wires, respectively: CS slice selection signal SCLK clock letter MOSI master device data output and slave device data input MISO master device data input and slave device data output The Linux kernel uses a combination of CPOL and CPHA to represent the four working modes of the current SPI: CPOL＝0，CPHA＝0 SPI_MODE_0 CPOL＝0，CPHA＝1 SPI_MODE_1 CPOL＝1，CPHA＝0 SPI_MODE_2 CPOL＝1，CPHA＝1 SPI_MODE_3 CPOL : Represents the state of the initial level of the clock signal, 0 is the low level and 1 is the high level. CPHA : Is sampling along which clock, 0 is sampling along the first clock and 1 is sampling along the second clock. The waveforms of SPI's four working modes are as follows: Drive coding The following W25Q128FV Flash module as an example of a simple introduction to the preparation of SPI driver. Hardware connection The hardware connection between Firefly-RK3399 and W25Q128FV is shown in the following table: Makefile/Kconfig Add the corresponding driver file configuration in "kernel/drivers/spi/Kconfig": config SPI_FIREFLY tristate "Firefly SPI demo support " default y help Select this option if your Firefly board needs to run SPI demo. Add the corresponding driver file name in "kernel/drivers/spi/Makefile": obj-$(CONFIG_SPI_FIREFLY) += spi-firefly-demo.o Select the added driver file in config, such as: │ Symbol: SPI_FIREFLY [=y] │ Type : tristate │ Prompt: Firefly SPI demo support │ Location: │ -> Device Drivers │ -> SPI support (SPI [=y]) │ Defined at drivers/spi/Kconfig:704 │ Depends on: SPI [=y] && SPI_MASTER [=y] Configure the DTS nodes Add SPI driver node description in "kernel/arch/arm64/boot/dts/rockchip/rk3399-firefly-demo.dtsi", as shown below: /* Firefly SPI demo */ &spi1 { spi_demo: spi-demo@00{ status = "okay"; compatible = "firefly,rk3399-spi"; reg = <0x00>; spi-max-frequency = <48000000>; /* rk3399 driver support SPI_CPOL | SPI_CPHA | SPI_CS_HIGH */ //spi-cpha; /* SPI mode: CPHA=1 */ //spi-cpol; /* SPI mode: CPOL=1 */ //spi-cs-high; }; }; &spidev0 { status = "disabled"; }; status : set okay if you want to enable SPI, or disable if not. spi-demo@00 : since CS0 is used in this example, it is set to 00; if CS1 is used, it is set to 01. compatible : the attribute here must be compatible with the member of the structure in the driver: of_device_id. reg : this is consistent with spi-demo@00, set to: 0x00 in this example. spi-max-frequency : set the highest frequency used by spi here. Firefly-RK3399 supports up to 48000000. spi-cpha，spi-cpol : the working mode of spi is set here. The working mode of the module spi used in this example is SPI_MODE_0 or SPI_MODE_3. Here we choose SPI_MODE_0. If SPI_MODE_3 is used, open spi-cpha and spi-cpol in spi_demo. spidev0 : since spi_demo uses the same hardware resources as spidev0, we need to turn off spidev0. Define SPI drivers Create a new driver file in "kernel/drivers/spi/", such as: "spi- firefly-demo.c". Before defining the SPI driver, the user first defines the variable "of_device_id". "Of_device_id" is used to call the device information defined in the DTS file in the driver. The definition is as follows: static struct of_device_id firefly_match_table[] = { {.compatible = "firefly,rk3399-spi",},{},}; The "compatible" values here are consistent with those in the DTS file. Spi_driver is defined as follows: static struct spi_driver firefly_spi_driver = { .driver = { .name = "firefly-spi", .owner = THIS_MODULE, .of_match_table = firefly_match_table,}, .probe = firefly_spi_probe, }; Registration of SPI equipment "Static int __init spidev_init(void)" registers SPI driver with kernel: "spi_register_driver(&firefly_spi_driver);" If the kernel is successfully matched on startup, the SPI core will configure SPI's parameters (mode, speed, etc.) and call "firefly_spi_probe". Read-write SPI data Firefly_spi_probe USES two interface operations to read the ID of W25Q128FV: The firefly_spi_read_w25x_id_0 interface directly USES spi_transfer and spi_message to transmit data. The firefly_spi_read_w25x_id_1 interface USES the SPI interface spi_write_then_read to read and write data. After success, it will print: root@rk3399_firefly_box:/ # dmesg | grep firefly-spi [ 1.006235] firefly-spi spi0.0: Firefly SPI demo program [ 1.006246] firefly-spi spi0.0: firefly_spi_probe: setup mode 0, 8 bits/w, 48000000 Hz max [ 1.006298] firefly-spi spi0.0: firefly_spi_read_w25x_id_0: ID = ef 40 18 00 00 [ 1.006361] firefly-spi spi0.0: firefly_spi_read_w25x_id_1: ID = ef 40 18 00 00 Open SPI demo "spi-firefly-demo" is not opened by default. If necessary, the demo driver can be opened with the following patch: --- a/kernel/arch/arm64/boot/dts/rockchip/rk3399-firefly-demo.dtsi +++ b/kernel/arch/arm64/boot/dts/rockchip/rk3399-firefly-demo.dtsi @@ -64,7 +64,7 @@ /* Firefly SPI demo */ &spi1 {spi_demo: spi-demo@00{ - status = "disabled"; + status = "okay"; compatible = "firefly,rk3399-spi"; reg = <0x00>; spi-max-frequency = <48000000>; @@ -76,6 +76,6 @@ }; &spidev0 { - status = "okay"; + status = "disabled"; }; Note: Since "spi1_rxd" and "spi1_txd" feet can be reused as "uart4_rx" and "uart4_tx", the use of uart4 should be turned off as follows: kernel/arch/arm64/boot/dts/rockchip/rk3399-firefly-port.dtsi &uart4 { current-speed = <9600>; no-loopback-test; status = "disabled"; }; Common SPI interface Here are the common SPI API definitions: void spi_message_init(struct spi_message *m); void spi_message_add_tail(struct spi_transfer *t, struct spi_message *m); int spi_sync(struct spi_device *spi, struct spi_message *message) ; int spi_write(struct spi_device *spi, const void *buf, size_t len); int spi_read(struct spi_device *spi, void *buf, size_t len); ssize_t spi_w8r8(struct spi_device *spi, u8 cmd); ssize_t spi_w8r16(struct spi_device *spi, u8 cmd); ssize_t spi_w8r16be(struct spi_device *spi, u8 cmd); int spi_write_then_read(struct spi_device *spi, const void *txbuf, unsigned n_tx, void *rxbuf, unsigned n_rx); Interface usage Linux provides a SPI user interface with limited functionality. If IRQ or other kernel driver interfaces are not required, consider using "spidev" interface to write user-level programs to control SPI devices. The corresponding path in the Firefly-RK3399 development board is "/dev/spidev0.0". "spidev" corresponding driver code is "kernel/drivers/spi/spidev.c". The config in the kernel needs to select "SPI_SPIDEV": │ Symbol: SPI_SPIDEV [=y] │ Type : tristate │ Prompt: User mode SPI device driver support │ Location: │ -> Device Drivers │ -> SPI support (SPI [=y]) │ Defined at drivers/spi/Kconfig:684 │ Depends on: SPI [=y] && SPI_MASTER [=y] DTS configuration is as follows: &spi1 { status = "okay"; max-freq = <48000000>; spidev@00 { compatible = "linux,spidev"; reg = <0x00>; spi-max-frequency = <48000000>; }; }; Please refer to "spidev" for detailed instructions. FAQs Q1: SPI data transfer exception? A1 : Make sure the "IOMUX" configuration of SPI 4 pins is correct. Confirm that when TX sends data, TX pins have normal waveform, CLK frequency is correct, CS signal is pulled down, and mode matches the device.