On 2013-03-31 5:07 AM, veegee wrote:
> Hi all,
>=20
> I'm testing the I2C functionality on the PIC32MX220F032B with the
> i2cdetect program on a Raspberry Pi. i2cdetect simply prints out a table
> of all found addresses on an I2C bus. The slave address of my PIC is 0x42=
..
>=20
> For some reason, if I configure the I2C module on the PIC *without* the
> I2C_USE_RESERVED_ADDRESSES flag to I2CSetSlaveAddress, i2cdetect shows th=
is:
>=20
> Note that the meaning of I2C_USE_RESERVED_ADDRESSES according to the
> Microchip PIC32 I2C library is: "Disable reserved address protection,
> allowing responses to reserved addresses (violates I2C specification) ".
>=20
> # i2cdetect -y 0
>=20
>      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
> 00:          03 04 05 06 07 -- -- -- -- -- -- -- --
> 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 40: -- -- 42 -- -- -- -- -- -- -- -- -- -- -- -- --
> 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 70: -- -- -- -- -- -- -- --
>=20
> Note the unexpected 0x03, 0x04, 0x05, 0x06, and 0x07 addresses being
> detected.
>=20
>=20
> But if I *do* pass the I2C_USE_RESERVED_ADDRESSES flag like so:
>=20
> I2CSetSlaveAddress(
> 	I2C1, 0x42, 0,
> 	I2C_USE_7BIT_ADDRESS | I2C_USE_RESERVED_ADDRESSES
> );
>=20
> i2cdetect shows what I expect:
>=20
> # i2cdetect -y 0
>=20
>      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
> 00:          -- -- -- -- -- -- -- -- -- -- -- -- --
> 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 40: -- -- 42 -- -- -- -- -- -- -- -- -- -- -- -- --
> 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
> 70: -- -- -- -- -- -- -- --
>=20
>=20
> When I tested the same functionality on a PIC18F26K22, the behaviour was
> as expected, with only 0x42 showing up without any special reserved
> address use configuration flags. But for the PIC32, the behaviour seems
> to be the opposite of what I expect.
>=20
> Can anyone shed some light on this?
>=20


I figured it out. There's yet another bug in Microchip's disgustingly
messy and poorly implemented peripheral library.

I2C_USE_RESERVED_ADDRESSES is a macro for 0x800, which corresponds to a
logic 1 at bit 11 of the I2CxCON register. When set, strict reserved
addressing is enforced and the device does not respond to reserved
address space. Their library has it backwards.
--=20
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