Hello, i found a problem while using the driver at91_i2c.c from the arm linux project: It is never possible to do a write operation. The following is a description of the error: If you look at i2c_smbus_xfer_emulated() in i2c-core.c a message array msg[2] with 2 messages is initialized. In the second message (msg[1]) the flags member is always set to I2C_M_RD. So if you call any of the following methods -i2c_smbus_read_byte -i2c_smbus_write_byte -i2c_smbus_read_byte_data -i2c_smbus_write_byte_data the flag is set to I2C_M_RD. In the driver at91_i2c.c the bit MREAD of the TWI Master Mode Register is always set according to the flags member of the second message and this member is always set to I2C_M_RD. MREAD is responsible for read/write, so it is never possible to do a write operation. This is the answer of the Atmel people who maintain the i2c driver for the AT91RM9200: Hi Peter. Andrew forwarded me your e-mail concerning the possible change of at91_i2c.c you proposed to correct the explained I2C_M_RD bit which get set incorrectly in the I2C emulating function (i2c_smbus_xfer_emulated). I have looked at the code, and saw that your founding to be true ( well at least for the one I'm currently working on now which is linux-2.4.25-vrs2 ), that msg[1].flag is always READ. This however, as far as I can tell, is incorrect. What I do suggested to Andrew (and now to you) is not to change the at91_i2c.c module to work around the problem, but rather eliminate the source of the problem, thus rather fix the i2c_smbus_xfer_emulated function in i2c-core.c. So my recommendation would be to fix-up the emulation function by ensuring that msg[1].flags = msg[0].flags. This *should* fix the problem. By doing it this way, one also ensures that the at91_i2c driver stays generic and compatible between devices on the shared bus. So I suggest you contact the i2c maintainer/developers, and submitting a patch to the emulation function. This is now an i2c issue, and not an arm specific one. Hope this helps. Kind regards, Pieter Loubser wbr Peter -------------------------------------------------------------- Peter K?gler EL-ME AG Gewerbering 1 D-84072 Au i. d. Hallertau Tel.: +49 / 8752 / 864 - 527 Fax.: +49 / 8752 / 864 - 100 mailto.: p.koegler at el-me.de Web: www.el-me.de
