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
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