Thomas Chou wrote:
Reinhard Meyer wrote:
Whenever possible by the hardware, I make I2C_SDA/SCL(1) do a tri-state and I2C_TRISTATE and I2C_ACTIVE are empty.
Dear Mike,
I traced the i2c-gpio.c of linux and realized that there are potential bus contention with the current soft_i2c.c if the ports are not open-drained.
Reinhard suggested a solution, which was similar to what linux driver does. So I would withdraw my SDA patch.
For our i2c gpio framework, I added these changes and tested on my boards. Please check if it works on yours.
# ifndef I2C_ACTIVE # define I2C_ACTIVE do {} while (0) # endif
# ifndef I2C_TRISTATE # define I2C_TRISTATE do {} while (0) # endif
# ifndef I2C_SDA # define I2C_SDA(bit) \ if (bit) { \ gpio_direction_input(CONFIG_SOFT_I2C_GPIO_SDA); \ } else { \ gpio_direction_output(CONFIG_SOFT_I2C_GPIO_SDA, 0);\ } # endif
I didn't tristate SCL(1) because it cannot be tristated on some nios2 boards. As soft_i2c of u-boot didn't support clock stretching, it shouldn't matter.
Its even simpler, provided the hardware can do open collector. Here was my solution for AVR32AP7000:
int board_early_init_f(void) { ... #ifdef CONFIG_CMD_I2C /* set SCL and SDA to open drain gpio */ portmux_select_gpio(PORTMUX_PORT_A,(1<<SDA_PIN), PORTMUX_DIR_OUTPUT|PORTMUX_INIT_LOW|PORTMUX_OPEN_DRAIN); portmux_select_gpio(PORTMUX_PORT_A,(1<<SCL_PIN), PORTMUX_DIR_OUTPUT|PORTMUX_INIT_LOW|PORTMUX_OPEN_DRAIN); /* initialize i2c. note: params ignored in SOFT I2C */ i2c_init(0, 0); #endif ... }
/* I2C access functions */ #ifdef CONFIG_CMD_I2C
int iic_read(void) { return pio_get_input_value(GPIO_PIN_PA(SDA_PIN)); }
void iic_sda(int bit) { pio_set_output_value(GPIO_PIN_PA(SDA_PIN),bit); }
void iic_scl(int bit) { pio_set_output_value(GPIO_PIN_PA(SCL_PIN),bit); }
#endif /* CONFIG_CMD_I2C */
I realize now, that in the init I should set the initial port value to high, but AP7000 is history for me. I did make the access functions real functions and let the macros call them:
#define SDA_PIN 6 #define SCL_PIN 7 #define I2C_SOFT_DECLARATIONS int iic_read(void);\ void iic_sda(int);\ void iic_scl(int); #define I2C_ACTIVE #define I2C_TRISTATE #define I2C_READ iic_read() #define I2C_SDA(bit) iic_sda(bit) #define I2C_SCL(bit) iic_scl(bit) #define I2C_DELAY udelay(3)
THAT, of course is a personal preference. As simple as the functions are, they could be inline or the macro itself ;)
Reinhard