Zephyr Device Driver and Device Model - PowerPoint Presentation

Slide1

Zephyr Device Driver and Device Model

Computer Science & Engineering Department

Arizona State University

Tempe, AZ 85287

Dr. Yann-Hang Lee

yhlee@asu.edu

(480) 727-7507Slide2

Device Model

To support initializing all the drivers configured into the system

The driver fills in the pointer to the structure containing the function pointers to its API functions during driver initialization.

These structures are placed into the RAM section in initialization level order.To provide a generic type API for each type of driver (UART, SPI, I2C)can be used by fibers and tasks API calls may be blocked for synchronous IO operationsmust use proper mechanisms for blocking according to execution context, e.g., a nanokernel semaphore cannot be used when the context is a task. Synchronous calls API type device_sync_call_t inline functions device_sync_call_init() device_sync_call_init() device_sync_call_init()

1

typedef

struct

{

/**

Nanokernel

semaphore for fiber context */

struct

nano_sem

f_sem

;

#

ifdef

CONFIG_MICROKERNEL /* use microkernel semaphore */

struct

_

k_sem_struct

_

t_sem

;

ksem_t

t_sem

;

enum

device_sync_waiter

waiter;

bool

device_ready

;#

endif

}

device_sync_call_t

;Slide3

Driver APIs

The runtime device

struct

per driver instanceDEVICE_INIT()create device object and set it up for boot time initialization.DEVICE_AND_API_INIT()Create device object and set it up for boot time initialization. This also takes a pointer to driver API struct for link time pointer assignment.DEVICE_NAME_GET()Expands to the full name of a global device object.DEVICE_GET()Obtain a pointer to a device object by name.DEVICE_DECLARE()Declare a device object.2struct device {

struct device_config *config

;

void *

driver_api

;

void *driver_data; };

struct

device_config

{

char *name;

int

(*

init

)(

struct

device *device);

void *

config_info

;

};Slide4

Device Initialization – DEVICE_INIT()

defines a device object that is automatically configured by the kernel during system initialization

two static

struct __config##dev_name and __device_##dev_nameplace them in “.devconfig.init” and “init_ #level STRINGFFY(prio)” sectionsinvoke_sys_device_do_config_level() to call all device->init()3

#define DEVICE_AND_API_INIT(dev_name, drv_name,

init_fn

, data,

cfg_info

, level,

prio, api) \ \ static struct

device_config

__

config

_##

dev_name

__used \

__attribute__((__section__(".

devconfig.init

"))) = { \

.name =

drv_name

, \

.

init

= (

init_fn

), \

.

config_info

= (

cfg_info

) \

}; \

\

static

struct

device (__device_##

dev_name

) __used \

__attribute__((__section__(".

init

_" #level STRINGIFY(

prio

)))) = { \

.

config

= &(__

config

_##

dev_name

), \

.

driver_api

=

api

, \

.

driver_data

= data \

}Slide5

Driver Example: i2c_dw

DEVICE_AND_API_INIT(i2c_0, CONFIG_I2C_DW_0_NAME, &i2c_dw_initialize,

&i2c_0_runtime, &i2c_config_dw_0,

SECONDARY, CONFIG_I2C_INIT_PRIORITY);initialization func – i2c_dw_initialize()driver API functionsconfig_data and driver_data4static struct i2c_driver_api funcs = { .configure = i2c_dw_runtime_configure, .transfer = i2c_dw_transfer,

.suspend = i2c_dw_suspend, .resume = i2c_dw_resume,};

struct

i2c_dw_dev_config {

device_sync_call_t

sync; union

dev_config

app_config

;

uint8_t *

xfr_buf

;

uint32_t

xfr_len

; uint32_t rx_pending; uint16_t hcnt; uint16_t lcnt; volatile uint8_t state; /* last dir. of transfer */ uint8_t request_bytes; uint8_t xfr_flags; bool support_hs_mode;};

struct

i2c_dw_rom_config {

uint32_t

base_address

;

uint32_t

irq_num

;

uint32_t

interrupt_mask

;

#

ifdef

CONFIG_PCI

struct

pci_dev_info

pci_dev

;

#

endif

/* CONFIG_PCI */

i2c_isr_cb_t

config_func

;

#

ifdef

CONFIG_I2C_DW_SHARED_IRQ

char *

shared_irq_dev_name

;

#

endif

/* CONFIG_I2C_DW_SHARED_IRQ */

};Slide6

Bit-Transfer on I2C Bus

One clock pulse is generated for each data bit that is transferred

Data Validity

The data on the SDA line must be stable during the HIGH(1) period of the clock. The data line(SDA) can change data only when the clock signal (SCL) is LOW(0)Wired-and functionopen-drain or open-collector

5Slide7

Data Transfer With 7-Bit Device Address

After START condition (S), a slave address(7-bit) is sent.

A read/write (R/W’) direction is then sent(8th bit)

Data transfer occurs, and then always terminated by STOP condition. However, repeated START conditions can occur.

6Slide8

Master-Transmitter to Slave-Receiver Data Transfer

In this, the transmission direction never changes. The set-up and transfer is straight-forward

7Slide9

Master-Receiver and Slave-Transmitter Data Transfer

Master initiates the data transfer by generating the START condition followed by the start byte (with read/write bit set to 1 i.e. read mode)

After the first

ack from the slave, the direction of data changes and the master becomes receiver and slave transmitter.The STOP condition is still generated by the master (master sends not-ACK before generating the STOP)

8Slide10

Example I2C Device – 24FC256 EEPROM

32K bytes in 512 pages of 64 bytes

I2C interface with A2, A1, A0 address pins

Page write operation:Random read operation:

9Slide11

Use of I2C Driver in Galileo Board

CONFIG_I2C_0=y in /zephyr/boards/

galileo

/galileo_defconfigI2C interface wrapper in /zephyr/include/i2c.h static int i2c_transfer(struct device *dev, struct i2c_msg *msgs, uint8_t num_msgs, uint16_t addr)Need to find the “struct device”Search the device objects by configuration nameWith DEVICE_INIT macro, the objects are placed in memory by the linker. 10

struct

device *

device_get_binding

(char *name) {

struct device *info; for (info = __device_init_start; info != __

device_init_end

; info++) {

if (!

strcmp

(name, info->

config

->name)) {

return info; }

}

return NULL;}