Merge pull request #1505 from stevew817/feature/new/fast_i2c

[Silicon Labs] Allow faster I2C baudrates

Author: 0xc0170

libraries/mbed/targets/hal/TARGET_Silicon_Labs/TARGET_EFM32/i2c_api.c

@@ -107,6 +107,10 @@ void i2c_init(i2c_t *obj, PinName sda, PinName scl)
     I2CName i2c_scl = (I2CName) pinmap_peripheral(scl, PinMap_I2C_SCL);
     obj->i2c.i2c = (I2C_TypeDef*) pinmap_merge(i2c_sda, i2c_scl);
     MBED_ASSERT(((int) obj->i2c.i2c) != NC);
+    
+    /* You need both SDA and SCL for I2C, so configuring one of them to NC is illegal */
+    MBED_ASSERT((uint32_t)sda != (uint32_t)NC);
+    MBED_ASSERT((uint32_t)scl != (uint32_t)NC);
 
     /* Enable clock for the peripheral */
     CMU_ClockEnable(i2c_get_clock(obj), true);
@@ -132,6 +136,8 @@ void i2c_init(i2c_t *obj, PinName sda, PinName scl)
 #endif
 
     /* Set up the pins for I2C use */
+    /* Note: Set up pins in higher drive strength to reduce slew rate */
+    /*   Though this requires user knowledge, since drive strength is controlled per port, not pin */
     pin_mode(scl, WiredAndPullUp);
     pin_mode(sda, WiredAndPullUp);
 
@@ -192,7 +198,23 @@ void i2c_frequency(i2c_t *obj, int hz)
 {
     /* Set frequency. As the second argument is 0,
      *  HFPER clock frequency is used as reference freq */
-    I2C_BusFreqSet(obj->i2c.i2c, REFERENCE_FREQUENCY, hz, i2cClockHLRStandard);
+    if (hz <= 0) return;
+    /* In I2C Normal mode (50% duty), we can go up to 100kHz */
+    if (hz <= 100000) {
+        I2C_BusFreqSet(obj->i2c.i2c, REFERENCE_FREQUENCY, hz, i2cClockHLRStandard);
+    }
+    /* In I2C Fast mode (6:3 ratio), we can go up to 400kHz */
+    else if (hz <= 400000) {
+        I2C_BusFreqSet(obj->i2c.i2c, REFERENCE_FREQUENCY, hz, i2cClockHLRAsymetric);
+    }
+    /* In I2C Fast+ mode (11:6 ratio), we can go up to 1 MHz */
+    else if (hz <= 1000000) {
+        I2C_BusFreqSet(obj->i2c.i2c, REFERENCE_FREQUENCY, hz, i2cClockHLRFast);
+    }
+    /* Cap requested frequency at 1MHz */
+    else {
+        I2C_BusFreqSet(obj->i2c.i2c, REFERENCE_FREQUENCY, 1000000, i2cClockHLRFast);
+    }
 }
 
 /* Creates a start condition on the I2C bus */
@@ -352,11 +374,15 @@ int block_and_wait_for_ack(I2C_TypeDef *i2c)
 void i2c_slave_mode(i2c_t *obj, int enable_slave)
 {
     if(enable_slave) {
+        /* Reference manual note: DIV must be set to 1 during slave operation */
+        obj->i2c.i2c->CLKDIV = 1;
         obj->i2c.i2c->CTRL |= _I2C_CTRL_SLAVE_MASK;
         obj->i2c.i2c->CTRL |= _I2C_CTRL_AUTOACK_MASK; //Slave implementation assumes auto acking
     } else {
         obj->i2c.i2c->CTRL &= ~_I2C_CTRL_SLAVE_MASK;
         obj->i2c.i2c->CTRL &= ~_I2C_CTRL_AUTOACK_MASK; //Master implementation ACKs manually
+        /* function is only called with enable_slave = false through i2c_init(..), so frequency is
+           already guaranteed to be set */
     }
 }