CXM_REG_I2C_SETSDA
CSR_WRITE_4(sc, CXM_REG_I2C_SETSDA, ~(int)1);
CSR_READ_4(sc, CXM_REG_I2C_SETSDA);
CSR_WRITE_4(sc, CXM_REG_I2C_SETSDA, ~(int)(val ? 1 : 0));