I2C implementation question - Linux on OMAP L138 using LogicPD's Zoom EVM Development Kit

Steven Roth

I have been stuck for a while on trying to get 2 GPIO pins set up for use in the I2C bit-banging GPIO driver in Linux. I believe that I have the pinmux settings correct:

From da850.c:
MUX_CFG(DA850, GPIO0_0, 1, 28, 15, 8, false)
MUX_CFG(DA850, GPIO0_6, 1, 4, 15, 8, false)

I have registered the board info and now get Linux to believe that the bus is there at boot time:
…
i2c-gpio i2c-gpio.1: using pins 20 (SDA) and 21 (SCL)
i2c-gpio i2c-gpio.2: using pins 6 (SDA) and 0 (SCL) <== Pins that I specified and registered in board-da850-evm.c
…

Using i2ctools, I can see this with i2cdetect:
root@arago:~/i2ctools# ./i2cdetect -l
i2c-1 i2c i2c-gpio1 I2C adapter
i2c-2 i2c i2c-gpio2 I2C adapter <== My adapter

However, when I look at that bus (./i2cdetect 2), nothing shows up. I have the dev board connected to a Sparkfun temperature sensor via J30, with SDA on pin 17, SCL on pin 92 and ground on pin 80. Power (3.3v) is supplied via the Sparkfun processor/power board. Correct voltages were measured at the temperature sensor but no pulses appear on the SCL line.

I think I am missing something in the driver setup. Can somebody give me a little shove in the right direction?

over 14 years ago

0 Norman Wong over 14 years ago

Guru 26430 points

Sounds like you have make all the changes to the code. Double check:

---arch/arm/mach-davinci/da850.c---

static const struct mux_config da850_pins[] = {
#ifdef CONFIG_DAVINCI_MUX
   /* UART0 function */
...
   MUX_CFG(DA850, ECAP2_APWM2,   1,   0,   15,   4,   false)

   /* More GPIO function */                           /* Add */
   MUX_CFG(DA850, GPIO0_0,       1,   28,   15,   8,   false) /* Add */
   MUX_CFG(DA850, GPIO0_6,       1,   4,   15,   8,   false) /* Add */
#endif
};

---arch/arm/mach-davinci/include/mach/mux.h---

enum davinci_da850_index {
   /* UART0 function */
   DA850_NUART0_CTS,
...
   DA850_ECAP2_APWM2,

   /* More GPIO function */ /* Add at end of list */
   DA850_GPIO0_0, /* Add at end of list */
   DA850_GPIO0_0, /* Add at end of list */
};

---arch/arm/mach-davinci/board-da850-evm.c---
...
static const short da850_evm_i2c_gpio2_pins[] = {
   DA850_GPIO0_0,
   DA850_GPIO0_6,
   -1
};
...
static __init void da850_evm_init(void)
{
...
   ret = davinci_cfg_reg_list(da850_evm_i2c_gpio2_pins);
   if (ret)
       pr_warning("da850_evm_init: i2c_-pio2 setup failed: %d\n", ret);
...
}

Those pins may get muxed in for other modules. The da850.c file gives the ones that are defined and might be used:

MUX_CFG(DA850,   AXR_8,       1,   28,   15,   1,   false)
MUX_CFG(DA850,   MCBSP1_CLKS,   1,   28,   15,   2,   false)
MUX_CFG(DA850,   ECAP1_APWM1,   1,   28,   15,   4,   false)

MUX_CFG(DA850,   AXR_14,       1,   4,   15,   1,   false)
MUX_CFG(DA850,   MCBSP1_CLKR,   1,   4,   15,   2,   false)

Check you board.c file to see if there is any intiialization that is muxing your pins away from your GPIO function.

I believe bit-bang I2C via GPIO still require pull-ups resistors on the SCL and SDA.

0 Steven Roth over 14 years ago in reply to Norman Wong

Prodigy 20 points

Norman,

Thanks for the reply! I think I am much farther along now due to your assistance. I was missing the following piece:

static __init void da850_evm_init(void)
{
...
   ret = davinci_cfg_reg_list(da850_evm_i2c_gpio2_pins); <<<<========= The missing piece!
    if (ret)
       pr_warning("da850_evm_init: i2c_-pio2 setup failed: %d\n", ret);
...
}

Your comment about checking for other initialization that was muxing my pins was also good. I found that the McBSP was taking one of my pins and since we aren't planning on using it, I disabled it in the kernel configuration.

Thanks for your assistance!

Steve

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I2C implementation question - Linux on OMAP L138 using LogicPD's Zoom EVM Development Kit