Add support for soft serial to ATmega32U2 (#10204)

* Add support for soft serial to ATmega32U2

* Update drivers/avr/serial.c

* Update drivers/avr/serial.c

* Update drivers/avr/serial.c

* Fix comment

* Update drivers/avr/serial.c

common_features.mk

@@ -428,8 +428,10 @@ ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
         # Functions added via QUANTUM_LIB_SRC are only included in the final binary if they're called.
         # Unused functions are pruned away, which is why we can add multiple drivers here without bloat.
         ifeq ($(PLATFORM),AVR)
-            QUANTUM_LIB_SRC += i2c_master.c \
-                               i2c_slave.c
+            ifneq ($(NO_I2C),yes)
+                QUANTUM_LIB_SRC += i2c_master.c \
+                                   i2c_slave.c
+            endif
         endif
 
         SERIAL_DRIVER ?= bitbang

drivers/avr/serial.c

@@ -20,11 +20,11 @@
 
 #ifdef SOFT_SERIAL_PIN
 
-#    ifdef __AVR_ATmega32U4__
-// if using ATmega32U4 I2C, can not use PD0 and PD1 in soft serial.
+#    if defined(__AVR_ATmega16U2__) || defined(__AVR_ATmega32U2__) || defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__)
+// if using ATmegaxxU4 I2C, can not use PD0 and PD1 in soft serial.
 #        ifdef USE_AVR_I2C
 #            if SOFT_SERIAL_PIN == D0 || SOFT_SERIAL_PIN == D1
-#                error Using ATmega32U4 I2C, so can not use PD0, PD1
+#                error Using ATmegaxxU4 I2C, so can not use PD0, PD1
 #            endif
 #        endif
 
@@ -52,7 +52,7 @@
 #                define EICRx_BIT (~(_BV(ISC30) | _BV(ISC31)))
 #                define SERIAL_PIN_INTERRUPT INT3_vect
 #            endif
-#        elif SOFT_SERIAL_PIN == E6
+#        elif (defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__)) && SOFT_SERIAL_PIN == E6
 #            define EIMSK_BIT _BV(INT6)
 #            define EICRx_BIT (~(_BV(ISC60) | _BV(ISC61)))
 #            define SERIAL_PIN_INTERRUPT INT6_vect
@@ -61,7 +61,7 @@
 #        endif
 
 #    else
-#        error serial.c now support ATmega32U4 only
+#        error serial.c currently only supports ATmegaxxU2 and ATmegaxxU4
 #    endif
 
 #    define ALWAYS_INLINE __attribute__((always_inline))

quantum/mcu_selection.mk

@@ -318,6 +318,9 @@ ifneq (,$(filter $(MCU),atmega16u2 atmega32u2 atmega16u4 atmega32u4 at90usb646 a
   ifeq (,$(filter $(NO_INTERRUPT_CONTROL_ENDPOINT),yes))
     OPT_DEFS += -DINTERRUPT_CONTROL_ENDPOINT
   endif
+  ifneq (,$(filter $(MCU),atmega16u2 atmega32u2))
+    NO_I2C = yes
+  endif
 endif
 
 ifneq (,$(filter $(MCU),atmega32a))