GC_I2C_BCR
reg = inreg(i2c, GC_I2C_BCR);
outreg(i2c, GC_I2C_BCR, par->i2c_rs ? I2C_REPEATED_START : I2C_START);
outreg(i2c, GC_I2C_BCR, I2C_START);
outreg(i2c, GC_I2C_BCR, I2C_START | (last ? 0 : I2C_ACK));
outreg(i2c, GC_I2C_BCR, I2C_STOP);