some functions to communicate with the mcp adc

firmware/mcp_adc.c

@@ -0,0 +1,66 @@
+#include <sys/types.h>
+
+/* analog digital converter
+ * scratchpad
+ * 
+ * address: 1101000
+ * read: conv data: 2 byte + config
+ * - ignore first 2 bits, bit 3 = MSB/sign
+ * - keeping reading always gets config byte
+ * write: config
+ * 
+ * configuration register:
+ * - 0x15 continuos conversion, 14bit, gain x2 (page 16)
+ * - 0x05 single conversion, 14bit, gain x2 (page 16)
+ * bit 7 low -> new data, set to 1 on single conv mode to init
+ *
+ */
+
+#define ADC_NEW_SAMPLE 0x80
+#define ADC_BITS_MASK 0x0c
+
+#define ADC_ADDR 0xD0 /* or 0x68 */
+
+void mcpadc_init(uint8_t mode)
+{
+	i2c_write(ADC_ADDR, 1, &mode))
+}
+
+uint8_t mcpadc_has_new_data()
+{
+	uint8_t r[4];
+	i2c_read(ADC_ADDR, 4, r)/* 4 bytes are only needed in 18 bit mode */
+	return r[3] & ADC_NEW_SAMPLE;
+}
+
+#if ADC_ENABLE_18_BIT_MODE
+int32_t mcpadc_get_data()
+{
+	uint8_t r[4] = 0;
+	int32_t value = 0;
+	i2c_read(ADC_ADDR, 4, r);/* reading 4 bytes guarantees us one config byte */
+	if(r[0] & 0x80) {value = 0xffff;}
+	value = (value << 16) | (r[0] << 8) | r[1];/*endianess ???*/
+	if((uint8_t) r[3] & ADC_BITS_MASK == ADC_BITS_18)
+	{
+		value = (value << 8) | r[3];
+	}
+	return value;
+}
+#else
+int16_t mcpadc_get_data()
+{
+	uint8_t r[2] = 0;
+	i2c_read(ADC_ADDR, 2, r);/* this will NOT work in 18 bit mode */
+	int16_t value = (r[0] << 8) | r[1];/*endianess ???*/
+	return r;
+}
+#endif
+
+void mcpadc_start_conv()
+{
+	uint8_t r[4];
+	i2c_read(ADC_ADDR, 4, r);
+	r[3] |= ADC_NEW_SAMPLE;
+	i2c_write(ADC_ADDR, 1, &(r[3]));
+}

firmware/mcp_adc.h

@@ -0,0 +1,54 @@
+#ifndef MCPADC_H
+#define MCPADC_H
+
+/*
+
+used i2c functions:
+
+i2c_read(uint8_t address, uint length, uint8_t *buf);
+i2c_write(uint8_t address, uint length, uint8_t *buf);
+
+*/
+
+#define ADC_ENABLE_18_BIT_MODE 0
+
+#define ADC_GAIN_1 0x00
+#define ADC_GAIN_2 0x01
+#define ADC_GAIN_4 0x02
+#define ADC_GAIN_8 0x03
+
+#define ADC_BITS_12 0x00
+#define ADC_BITS_14 0x04
+#define ADC_BITS_16 0x08
+#if ADC_ENABLE_18_BIT_MODE
+# define ADC_BITS_18 0x0c
+#endif
+
+#define ADC_CONV_SINGLE 0x00
+#define ADC_CONV_CONT 0x10
+
+/* sets the mcp adc to the specified mode
+ * valid modes are obtained by oring one of each group (ADC_GAIN_*, ADC_BITS_* and ADC_CONV_*) together
+ */
+void mcpadc_init(uint8_t const mode);
+
+/* tests if the adc has a new sample
+ * returns nonzero if new data is aviable, 0 otherwise
+ */
+uint8_t mcpadc_has_new_data();
+
+/* returns the most recent sample result of the adc
+ * !! return type depends on defines
+ */
+#if ADC_ENABLE_18_BIT_MODE
+int32_t mcpadc_get_data();
+#else
+int16_t mcpadc_get_data();
+#endif
+
+/* instructs the adc to take a new sample now
+ * has no effect if the current mode includes ADC_CONV_CONT
+ */
+void mcpadc_start_conv();
+
+#endif