Real-time Systems Lab, Computer Science and Engineering, ASU Quark SPI Interface (ESP – Fall 2014) Computer Science & Engineering Department Arizona State University Tempe, AZ Dr. Yann-Hang Lee (480)

Real-time Systems Lab, Computer Science and Engineering, ASU  A duplex, synchronous, serial communication between CPU and peripheral devices  Master mode and slave mode  Bi-directional mode  Synchronous serial clock  Signals:  MOSI: master out slave in  MISO: master in slave out  SS: select signal from master to slave  SCK: serial clock Serial Peripheral Interface (SPI) MOSI MISO SCK SS1 SS2 MOSI MISO SCK SS MOSI MISO SCK SS processor peripheral 2 peripheral 1 1

Real-time Systems Lab, Computer Science and Engineering, ASU SPI Operation  Data registers in the master and the slave form a distributed register.  When a data transfer operation is performed, this distributed register is serially shifted by the SCK clock from the master  Can shift in burst mode shift reg. MOSI MISO transmit data reg receive data reg transmit data reg receive data reg 2

Real-time Systems Lab, Computer Science and Engineering, ASU CPOL and CPHA (Polarity and Phase)  CPHA=0 – the first edge on the SCK line is used to clock the first data bit (the first bit of the data must be ready when selected)  CPHA=1 – if required, the first SCK edge before the first data bit becomes available at the data out pin 3

Real-time Systems Lab, Computer Science and Engineering, ASU SPI Interface on Quark  Three controllers: SPI0 and SPI1 + Lagecy SPI  On Galileo  LSPI  flash memory  SPI0  ADC  SPI1  IO pins  Does not use SPIx_SS signals  gpio 8  SPI0_CS  gpio10  SPI1_CS  Similar to the SPI of PXA2xx chip (Xscale) 4

Real-time Systems Lab, Computer Science and Engineering, ASU SPI Drivers on Quark 5 SPI core (spi.c) spidev SPI chip driver (pxa2xx.c, pxa2xx-pci.c) SPI device driver1 SPI device driver2 user space kernel hardware SPI controllers /dev/spidev1.0 /dev/ledmatrix /dev/xxx

Real-time Systems Lab, Computer Science and Engineering, ASU SPI Drivers  Driver for SPI devices  protocol driver bound to a spi_device  Driver for SPI chips (controller)  IO model  queued messages submitted by protocol drivers  spi_message : a list of spi_transfer  struct spi_transfer object for a full duplex SPI transfer  write-only if NULL in rx_buf  spi_async or spi_sync to submit message  spi_async -- must wait for the completion callback before accessing the data buffers in the spi_transfer records 6 struct spi_transfer { const void *tx_buf; void *rx_buf; unsigned len; dma_addr_t tx_dma; dma_addr_t rx_dma; unsigned cs_change:1; u8 bits_per_word; u16 delay_usecs; u32 speed_hz; struct list_head transfer_list; };

Real-time Systems Lab, Computer Science and Engineering, ASU Key Data Structures for SPI Drivers  spi_message  spi_device (spi_add_device)  spi_driver (spi_register_driver)  spi_master (spi_register_master) 7 struct spi_message { struct list_head transfers; struct spi_device *spi; unsigned is_dma_mapped:1; void (*complete)(void *context); void *context; unsigned actual_length; int status; struct list_head queue; void *state; }; struct spi_device { struct device dev; struct spi_master * master; u32 max_speed_hz; u8 chip_select; u8 bits_per_word; u16 mode; int irq; void * controller_state; void * controller_data; char modalias[SPI_NAME_SIZE]; int cs_gpio; };

Real-time Systems Lab, Computer Science and Engineering, ASU Linux spidev  a limited userspace API, supporting basic half-duplex read() and write() access to SPI slave  /dev/spidevB.C – for chipselect C on bus B  use ioctl() to set up transfer mode (bits_per_word, lsb_first, …etc)  read() and write() for half-duplex operations 8 spidev_sync_write(struct spidev_data *spidev, size_t len) { struct spi_transfer t = {.tx_buf = spidev->buffer,.len = len,}; struct spi_message m; spi_message_init(&m); spi_message_add_tail(&t, &m); return spidev_sync(spidev, &m); }

Real-time Systems Lab, Computer Science and Engineering, ASU Construct and Use SPI Interface  In spidev, when init, register spi_driver (spi_register_driver)  add driver to SPI bus (driver_register)  create device spidevB.C  In spi-pxa2xx.c  call spi_register_master() to register a SPI master  set up properties for SPI bus master (bus number, irq, bits_per_word, etc.)  When spidev_sync is called   spi_async (spidev->spi, message) // spi_device  spi->master  message->spi  master->transfer  tasklet_schedule(pump_transfer)  when done  spi_finalize_current_message and  complete(context)  wait for completion 9