Quark GPIO and I2C
(ESP – Fall 2014)
Computer Science & Engineering Department
Arizona State University
Tempe, AZ 85287
Dr. Yann-Hang Lee
yhlee@asu.edu
(480) 727-7507
Real-time Systems Lab, Computer Science and Engineering, ASU
GPIO interface
 From programmer’s view
 GPIO pin numbering
 enable GPIO (pin multiplexing)
 set direction
 read/write data
 interrupt
 There may be various physical connections
 GPIO pins in IO expender
 GPIO ports
 GPIO devices on PCI bus
 various GPIO controllers
 GPIO driver (user-level interface) : /driver/gpio/gpiolib.c
 Drivers for gpio chips
 For Galileo board:
 gpio_sch.c (Poulsbo SCH) + intel_cln_gip_gpio.c + cy8c9540a.c
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GPIO Sysfs Interface
 Example of shell commands for GPIO:
 echo -n $led > /sys/class/gpio/export
 echo -n $DIR > /sys/class/gpio/gpio$led/direction
 echo -n $ON > /sys/class/gpio/gpio$led/value
 Sysfs interface
 to export kernel data structures, their attributes, and the linkages
between them to user space.
 two methods for read and write operations
struct device_attribute {
struct attribute
attr;
ssize_t (*show)(struct device *dev, ….);
ssize_t (*store)(struct device *dev, ….);
};
 So, in gpiolib.c, the following functions are provided
export_store(), gpio_value_store(), gpio_direction_show(), ….
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Linux GPIO Driver
 A GPIO (General Purpose Input/Output) pin can be configured,
set up its direction, and value if it is an output pin
 A SoC chip may have several GPIO components
 Multiple “gpio chips”
 A global number in the integrated GPIO namespace, i.e., 0, 1,
2,…,n
 sysfs interface to user space
GPIO framework
(gpiolib.c)
CY8C9540A
40 GPIO pins in 6 ports
Quark GIP
controller
Quark legacy
GPIO[7:0]
GPIO_SUS[5:0]
GPIO[9:8]
GPIO
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GPIO on Galileo (1)
Quark X1000
Sysfs
GPIO #
Signal Name / Arduino Port #
Function and Comments
GPIO_SUS0
GPIO_SUS1
GPIO_SUS2
gpio2
gpio3
gpio4
INT_N_S3
GP LED
LVL_OE
Don’t touch, or bad things will happen :-)
LED between CY8C9540A and RTC battery
TXS0108E level shifter output enable.
GPIO_SUS3
gpio5
GPIO_SUS3_PCIE_RESET_N
Reset to Mini PCI-E slot
GPIO_SUS4
gpio6
GPIO_SUS4_W_DISABLE_N
Wireless disable (RF Kill to PCI-E Slot)
GPIO_SUS5
gpio7
A0_N
Jumper J2 (Cypress CY8C9540A I2C
address select)
GPIO0
GPIO1
gpio8
gpio9
SPI0_CS_N
Not Connected
Select SPI for AD7298
GPIO2
gpio10
SPI1_CS_N
Routed to IO10 if selected by IO10_MUX
GPIO3
GPIO4
GPIO5
GPIO6
GPIO7
GPIO8
GPIO9
gpio11
gpio12
gpio13
gpio14
gpio15
gpio0
gpio1
Not Connected
XRES
INT_N_S0
IO2
IO3
GLN_IO2_PU_EN
GLN_IO3_PU_EN
Reset to Cypress CY8C9540A
Don’t touch too :-)
Selected by IO2_MUX (gpio31=0)
Selected by IO3_MUX (gpio30=0)
Enable pullup on IO2/GPIO6
Enable pullup on IO3/GPIO7
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GPIO on Galileo (1)
CY8C9540A
Sysfs GPIO Signal Name /
#
Arduino Port #
GPORT0_BIT0
gpio16
IO10
GPORT0_BIT1
gpio17
IO5
GPORT0_BIT2
gpio18
IO3
GPORT0_BIT3
gpio19
IO9
GPORT0_BIT4
gpio20
A5_MUX
GPORT0_BIT5
gpio21
A4_MUX
GPORT0_BIT6
gpio22
A3_MUX
GPORT0_BIT7
gpio23
A2_MUX
GPORT1_BIT0
gpio24
IO6
GPORT1_BIT1
gpio25
IO11
GPORT1_BIT2
gpio26
IO8
Function and Comments
Selected by IO10_MUX (GPORT3_BIT6, gpio42)
Also controlled by pwm7
Also controlled by pwm5
Selected by IO3_MUX (gpio30=1)
Also controlled by pwm3
Also controlled by pwm1
A5 pin routing: 0 = AD7298 (VIN5)
1 = Cypress CY8C9540A (GPORT4_BIT5, gpio49)
A4 pin routing: 0 = AD7298 (VIN4)
1 = Cypress CY8C9540A (GPORT4_BIT4, gpio48)
A3 pin routing: 0 = AD7298 (VIN3)
1 = Cypress CY8C9540A (GPORT4_BIT3, gpio47)
A2 pin routing: 0 = AD7298 (VIN2)
1 = Cypress CY8C9540A (GPORT4_BIT2, gpio46)
Also controlled by pwm6
Selected by IO11_MUX (GPORT3_BIT7, gpio43)
Also controlled by pwm4
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GPIO on Galileo (2)
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GPIO Chip Driver
 A driver for each GPIO controller to provide
 methods to establish GPIO direction and to access GPIO values
 method to return the IRQ number associated to a given GPIO
 flag saying whether calls to its methods may sleep
 optional base number
 In intel_qrk_gip_gpio.c
/* The base GPIO number under GPIOLIB framework */
#define INTEL_QRK_GIP_GPIO_BASE
8
/* The default number of South-Cluster GPIO on Quark. */
#define INTEL_QRK_GIP_NGPIO
8
 In include/linux/gpio/driver.h, “gpio_chip” is defined, including
 base: identifies the first GPIO number handled by this chip.
 ngpio: the number of GPIOs handled by this controller; the last GPIO
handled is (base + ngpio - 1).
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Binding of GPIOs to Pins
 Example: gpio 26 is bit 2 of port 1 in CY8C9540A chip
 Each GPIO chip is represented by “struct gpio_chip”
 standard methods such as get, set, etc.
 “int base;” and “u16 ngpio;”
 When a gpio chip is added, use “base” and “ngpio” to
determine “pin range” of the chip
 In cy8C9540a.c
#define NGPIO
40
static const u8 cy8c9540a_port_offs[] = {0, 8, 16, 20, 28, 36,};
#define GPIO_BASE_ID 16
 When cy8c9540a_gpio_get_value is called,
 an input argument: gpio=26
 invoke cypress_get_port(26) to find port 1
 invoke cypress_get_offs(26) to find bit 2
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GPIO Driver Operation
 GPIO chip driver request to add “gpio_chip” to the platform
gc->base = pdata->gpio_base;
gc->ngpio = NGPIO;
ret = gpiochip_add(&dev->gpio_chip);
 gpiolib.c exports methods to work on GPIO pins
 from GPIO # to find chip and to invoke teh corresponding
methods provided by the chip
gpio_request_one(LED1, GPIOF_OUT_INIT_LOW, "led1");
gpio_desc desc1 = gpio_to_desc(LED1);
gpio_set_value(desc1, data);
 sysfs gpio interfaces, such as
gpiod_export, gpio_unexport, gpiod_set_value,
gpio_direction_input
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GPIO Programming
 GPIO Programming
 In user space – via sysfs
int fd = open("/sys/class/gpio/export", O_WRONLY);
sprintf(buffer, "%d", gpio);
// int gpio
write(fd, buffer, strlen(buffer));
close(fd);
 In kernel space – use the exported interface of gpiolib.c
gpio_request_one(GP_3, GPIOF_OUT_INIT_LOW, "led1");
gpio_set_value(GP_3, 0);
 Poll and GPIO interrupt
 configure GPIO pin as an interrupt source via
/sys/class/gpio/gpioX/edge
 poll() system call to block on the gpio value until an interrupt
occurs. When the content changes, poll will return
POLLERR|POLLPRI.
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GIP controller in Quark
 A PCI device: B:0, D:21, F:2
 MMIO –
 use two base registers in configuration
registers
Offset Start
10h
14h
Offset End
13h
17h
Register ID
BAR0
BAR1
Default Value
00000000h
00000000h
 I2C memory registers – BAR0+offset
 I2C Master mode operation
 Disable the I2C controller by writing 0 to IC_ENABLE.ENABLE.
 Write to the IC_CON register
 Write to the IC_TAR register.
 Enable the I2C controller by writing a 1 in IC_ENABLE.
 Write the transfer direction and data to be sent to the IC_DATA_CMD
register.
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Quark GPIO IRQ Enable in GIP
 Allows each bit of Port A to be configured for interrupts.
 In drivers/mfd/intel_cln_gip_gpio.c,
#define PORTA_INT_EN
0x30/* Interrupt enable */
#define PORTA_INT_MASK
0x34/* Interrupt mask */
#define PORTA_INT_TYPE_LEVEL
0x38/* Interrupt level*/
.......
static void intel_cln_gpio_irq_enable(struct irq_data *d)
{....
void __iomem *reg_inte = reg_base + PORTA_INT_EN;
gpio = d->irq - irq_base;
spin_lock_irqsave(&lock, flags);
val_inte = ioread32(reg_inte);
iowrite32(val_inte | BIT(gpio % 32), reg_inte);
spin_unlock_irqrestore(&lock, flags);
}
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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 function
 open-drain or opencollector
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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.
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Master-Transmitter to Slave-Receiver Data Transfer
 In this, the transmission direction never changes. The set-up and
transfer is straight-forward
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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 notACK before generating the STOP)
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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:
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I2C Controller in Quark
 GIP controller: Bus 0, Device 21, Function 2
 PCI configuration registers
 Base Address Register (BAR0) — Offset 10h
 Base Address Register (BAR1) — Offset 14h
 I2C Controller Memory Mapped Registers – Based on BAR0
 register offsets are defined in /deriver/i2c/buses/i2c-designware-core.c
 I2C algorithm
static struct i2c_algorithm i2c_dw_algo = {
.master_xfer
= i2c_dw_xfer,
.functionality
= i2c_dw_func, };
 major steps of i2c_dw_xfer in i2c-designware-core.c,
i2c_dw_wait_bus_not_busy(dev);
i2c_dw_xfer_init(dev);
/* wait for tx to complete
*/
wait_for_completion_interruptible_timeout
 to write to control reg:
dw_writel(dev, 1, DW_IC_ENABLE); /* Enable the adapter */
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I2C Drivers in Linux
 A driver for I2C bus
 adapter and algorithm drivers
 manages I2C bus transactions
 Drivers for I2C devices
 A client has the device’s I2C bus
address and a pointer to a driver
which is attached with an adapter
 When a user program issues a file
operation that needs an I2C
transaction
 i2C_transfer (i2C-core.c) to invoke
adap_algo_master_xfer
 command or data is in an msg array
 the adapter issues reads/writes to
hardware I/O addresses.
(https://i2c.wiki.kernel.org/index.php/Driver_Architecture)
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I2C and SMBus
 In general, a system can have multiple I2C
buses via different adapters and many
I2C devices
 2-wire synchronous serial buses
 Master and slave, addressable
Processor
ICH8
SMBus
PCI bus
PCI to I2c
 I2C bus and SMBus
Adapter
EEPROM
 compatible with each other.
I2C
 Differences
EEPROM
 Timeout (in SMBus, reset interfaces when
sensor
clock is low forlonger than 35ms))
 Maximum clock speed: 100MHz(Smbus) but I2C bus has both 400kHz
and 3.4MHz versions.
 Logic level: 1: 3V in I2C and 2.1V in SMBus
 General call and alert response.
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Example of Accessing I2C/SMBus Devices
i2c_smbus_xfer(adapter, addr, …., data)
user
program
device
driver
I2C
core
I2C
algorithm
I2C
adapter
read(……)
I2C
device
I2C bus signals
12c_dw_xfer(adapter, msg[ ], num)
user space
kernel space
adapter->algo->i2c_transfer(adapter, msg, num);
// for each i2c device
struct i2c_client {
unsigned short flags;
unsigned short addr;
char name[I2C_NAME_SIZE];
struct i2c_adapter * adapter;
struct i2c_driver * driver;
struct device dev;
int irq;
struct list_head list;
struct completion released;
};
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Driver Operations (1)
 When intel_cln_gip_core module is installed,
 register itself as a PCI driver
 provide the probe callback function intel_cln_gip_probe which calls
intel_cln_i2c_probe of intel_cln_gip_i2c.c to initiate gip i2c controller
 In intel_cln_i2c_probe




construct and initiate a struct dw_i2c_dev to model dw_i2c controller
register it as a i2c adapter and add callback functions
struct i2c_adapter /* to identify a physical i2c bus */
struct i2c_algorithm /* the algorithm to access the bus*/
 i2c-dev – a char device driver to access all devices on an i2c
adapter from userspace
 user programs call “read”, “write”, “ioctl”, etc., to control i2c bus
transactions on an adapter (master).
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Driver Operations (2)
 i2c-dev creates a device i2c-x for each i2c adapter where “x” is
the adapter number, starting from 0.
 So, user program can
 open /dev/i2c-0
 set slave address, i.e. client->addr (the i2c address of the device on the
bus)
 write a “msg” to the bus with i2c_transfer in i2c-core.c which eventually
calls adap->algo->master_xfer
 In i2c_dw_xfer,
 lock the device
 check bus busy or not
 start the transfers -- i2c_dw_xfer_init
 wait for completion
 In i2c_dw_isr (isr for GIP i2c controller)
 indicates the completion of a transfer (complete(&dev->cmd_complete))
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