Incorporate raspberrypi#273

Author: dhalbert

src/rp2_common/hardware_i2c/i2c.c

@@ -85,6 +85,12 @@ uint i2c_set_baudrate(i2c_inst_t *i2c, uint baudrate) {
     i2c->hw->fs_scl_lcnt = lcnt;
     i2c->hw->fs_spklen = lcnt < 16 ? 1 : lcnt / 16;
 
+    // Set hold time of SDA during transmit to 2. The TCS34725 color sensor
+    // does not work without this change, and perhaps it helps other I2C
+    // devices as well. There is no discernable change slowdown in timing traces.
+    i2c->hw->sda_hold =
+        I2C_IC_SDA_HOLD_IC_SDA_RX_HOLD_RESET << I2C_IC_SDA_HOLD_IC_SDA_RX_HOLD_LSB |
+        2 << I2C_IC_SDA_HOLD_IC_SDA_TX_HOLD_LSB;
     i2c->hw->enable = 1;
     return freq_in / period;
 }