CXM_REG_I2C_SETSCL
CSR_WRITE_4(sc, CXM_REG_I2C_SETSCL, ~(int)1);
CSR_WRITE_4(sc, CXM_REG_I2C_SETSCL, ~(int)(val ? 1 : 0));
CSR_READ_4(sc, CXM_REG_I2C_SETSCL);