stm32: adc common v2: add circular dma mode

Tested only on the F3 so far.

include/libopencm3/stm32/common/adc_common_v2.h

@@ -205,7 +205,8 @@ bool adc_get_overrun_flag(uint32_t adc);
 void adc_clear_overrun_flag(uint32_t adc);
 uint32_t adc_read_regular(uint32_t adc);
 void adc_start_conversion_regular(uint32_t adc);
-
+void adc_enable_dma_circular_mode(uint32_t adc);
+void adc_disable_dma_circular_mode(uint32_t adc);
 END_DECLS
 
 #endif

lib/stm32/common/adc_common_v2.c

@@ -389,4 +389,24 @@ void adc_start_conversion_regular(uint32_t adc)
 	ADC_CR(adc) |= ADC_CR_ADSTART;
 }
 
+/** @brief Enable circular mode for DMA transfers
+ *
+ * For this to work it needs to be ebabled on the DMA side as well.
+ *
+ * @param[in] adc Unsigned int32. ADC base address (@ref adc_reg_base)
+ */
+void adc_enable_dma_circular_mode(uint32_t adc)
+{
+	ADC_CFGR1(adc) |= ADC_CFGR1_DMACFG;
+}
+
+/** @brief Disable circular mode for DMA transfers
+ *
+ * @param[in] adc Unsigned int32. ADC base address (@ref adc_reg_base)
+ */
+void adc_disable_dma_circular_mode(uint32_t adc)
+{
+	ADC_CFGR1(adc) &= ~ADC_CFGR1_DMACFG;
+}
+
 /**@}*/