I2C_M_CONTROL
HWRITE4(sc, I2C_M_CONTROL, divh << I2C_M_CONTROL_QTR_CLK_EXT_SHIFT |
HSET4(sc, I2C_M_CONTROL, I2C_M_CONTROL_START);
ctrl = HREAD4(sc, I2C_M_CONTROL);
HCLR4(sc, I2C_M_CONTROL, I2C_M_CONTROL_START);