diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
new file mode 100644
index 0000000..f663373
--- /dev/null
+++ b/.github/workflows/main.yml
@@ -0,0 +1,31 @@
+name: CI
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    timeout-minutes: 5
+
+    strategy:
+      matrix:
+        device: ['longan-nano', 'longan-nano-lite']
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install RISC-V build dependencies
+        run: sudo apt-get install build-essential binutils-riscv64-unknown-elf gcc-riscv64-unknown-elf
+
+      - name: Build the FiveForths firmware binary for ${{matrix.device}}
+        run: make ${{matrix.device}}
+
+      - name: Obtain SHA256 hash of the firmware ${{matrix.device}}.bin
+        run: sha256sum fiveforths.bin > fiveforths.bin.sha256
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: fiveforths-firmware-${{matrix.device}}
+          path: fiveforths.bin*
diff --git a/Makefile b/Makefile
index e47adae..fcaa335 100644
--- a/Makefile
+++ b/Makefile
@@ -4,8 +4,6 @@
 
 PROGNAME = fiveforths
 CFLAGS := -g
-ARCH ?= rv32imac # rv32imac for Longan Nano
-EMU ?= elf32lriscv
 CROSS ?= /usr/bin/riscv64-unknown-elf-
 AS := $(CROSS)as
 LD := $(CROSS)ld
@@ -13,15 +11,21 @@ OBJCOPY := $(CROSS)objcopy
 OBJDUMP := $(CROSS)objdump
 READELF := $(CROSS)readelf
 
+# MCU and board specific variables
+ARCH ?= rv32imac
+EMU ?= elf32lriscv
+MCU ?= gd32vf103
+BOARD ?= longan-nano-lite
+
 .PHONY: clean
 
 build: $(PROGNAME).o $(PROGNAME).elf $(PROGNAME).bin $(PROGNAME).hex $(PROGNAME).dump
 
 %.o: %.s
-		$(AS) $(CFLAGS) -march=$(ARCH) -I src -o $@ $<
+		$(AS) $(CFLAGS) -march=$(ARCH) -I src/boards/$(BOARD) -I src/mcus/$(MCU) -I src -o $@ $<
 
 %.elf: %.o
-		$(LD) -m $(EMU) -T $(PROGNAME).ld -o $@ $<
+		$(LD) -m $(EMU) -T src/boards/$(BOARD)/linker.ld -o $@ $<
 
 %.bin: %.elf
 		$(OBJCOPY) -O binary $< $@
@@ -44,5 +48,11 @@ openocd:
 debug:
 		/opt/riscv/bin/riscv64-unknown-elf-gdb -command=debug.gdb -q fiveforths.elf
 
+longan-nano:
+		$(MAKE) build BOARD=longan-nano
+
+longan-nano-lite:
+		$(MAKE) build BOARD=longan-nano-lite
+
 clean:
 		rm -v *.bin *.elf *.o *.hex *.dump
diff --git a/README.md b/README.md
index 9d5a878..613990f 100644
--- a/README.md
+++ b/README.md
@@ -30,12 +30,14 @@ Development progress has been logged regularly in the [devlogs](https://aw.githu
 
 # Getting started
 
+It is possible to download a firmware binary or build the firmware manually.
+
 ## Download it
 
 Download one of the firmware binaries from the [releases page](https://github.com/aw/fiveforths/releases).
 
-* [fiveforths-longan-nano-lite.bin](https://github.com/aw/fiveforths/releases/download/v0.1/fiveforths-longan-nano-lite.bin) (64K Flash, 20K RAM)
-* [fiveforths-longan-nano.bin](https://github.com/aw/fiveforths/releases/download/v0.1/fiveforths-longan-nano.bin) (128K Flash, 32K RAM)
+* [fiveforths-longan-nano-lite.bin](https://github.com/aw/fiveforths/releases/download/v0.2/fiveforths-longan-nano-lite.bin) (64K Flash, 20K RAM)
+* [fiveforths-longan-nano.bin](https://github.com/aw/fiveforths/releases/download/v0.2/fiveforths-longan-nano.bin) (128K Flash, 32K RAM)
 
 ## Build it
 
@@ -65,7 +67,7 @@ $ make
 /usr/bin/riscv64-unknown-elf-objdump -D -S fiveforths.elf > fiveforths.dump
 ```
 
-The firmware file is called `fiveforths.bin` and is **under 2 KBytes** as of _January 08, 2023_.
+The firmware file is called `fiveforths.bin` and is **under 2 KBytes** as of _release v0.1_ since _January 08, 2023_.
 
 # Flashing the firmware
 
@@ -121,7 +123,7 @@ The source files are:
 # TODO
 
 - [ ] Finish writing this README
-- [ ] Fix remaining bugs (carriage return issue)
+- [x] Fix remaining bugs (carriage return issue)
 - [ ] Implement bounds checks for stacks and dictionary
 - [ ] Code cleanup and optimizations
 - [ ] Add example Forth code to turn it into a "real" Forth (ex: `[`, `]`, `branch`, etc)
@@ -132,7 +134,14 @@ Please create a pull-request or [open an issue](https://github.com/aw/picolisp-k
 
 # Changelog
 
-* 2023-01-09 - First release
+## 0.2 (2023-01-10)
+
+  * Fix issue #9 - Handling of carriage return
+  * Fix issue #11 - Ignore non-printable characters
+  * Re-organize code to support different boards and MCUs
+  * Add GitHub action to automatically build and publish the firmware binaries
+
+## 0.1 2023-01-09 - First release
 
 # Other Forths
 
diff --git a/fiveforths.s b/fiveforths.s
index 2900e90..e0d4913 100644
--- a/fiveforths.s
+++ b/fiveforths.s
@@ -19,13 +19,16 @@ Copyright (c) 2021 Alexander Williams, On-Prem <license@on-premises.com>
 # s1 = IP  = instruction pointer
 # s2 = RSP = return stack pointer
 
+# include board-specific functions and constants from src/boards/<board>/
+.include "board.s"
+
+# include MCU-specific functions and constants from src/mcus/<MCU>/
+.include "mcu.s"
+
+# include source files from src/
 .include "01-variables-constants.s"
 .include "02-macros.s"
 .include "03-interrupts.s"
-
-# include board-specific functions
-.include "gd32vf103.s"
-
 .include "04-io-helpers.s"
 .include "05-internal-functions.s"
 .include "06-initialization.s"
diff --git a/src/01-variables-constants.s b/src/01-variables-constants.s
index 0b2a25d..b2bc6ee 100644
--- a/src/01-variables-constants.s
+++ b/src/01-variables-constants.s
@@ -8,12 +8,6 @@
 # Memory map
 ##
 
-# adjust these values for specific targets
-.equ CELL, 4                            # 32-bits cell size
-.equ RAM_BASE, 0x20000000               # base address of RAM
-.equ RAM_SIZE, 1024 * 20                # 20 KiB
-.equ STACK_SIZE, 256                    # 256 Bytes
-
 # DSP, RSP, TIB stacks grow downward from the top of memory
 .equ DSP_TOP, RAM_BASE + RAM_SIZE       # address of top of data stack
 .equ RSP_TOP, DSP_TOP - STACK_SIZE      # address of top of return stack
@@ -36,7 +30,7 @@
 ##
 
 .equ CHAR_NEWLINE, '\n'         # newline character 0x0A
-.equ CHAR_CARRIAGE, '\r'        # carriage return character 0x13
+.equ CHAR_CARRIAGE, '\r'        # carriage return character 0x0D
 .equ CHAR_SPACE, ' '            # space character 0x20
 .equ CHAR_BACKSPACE, '\b'       # backspace character 0x08
 .equ CHAR_COMMENT, '\\'         # backslash character 0x5C
diff --git a/src/09-interpreter.s b/src/09-interpreter.s
index cced749..3b3d940 100644
--- a/src/09-interpreter.s
+++ b/src/09-interpreter.s
@@ -14,6 +14,13 @@ interpreter:
     call uart_get                               # read a character from UART
     li t4, CHAR_NEWLINE                         # load newline into temporary
     beq a0, t4, skip_send                       # don't send the character if it's a newline
+
+    # ignore specific characters
+    mv t4, zero                                 # load 0x00 zero into temporary
+    beq a0, t4, interpreter                     # ignore the character if it matches
+    li t4, CHAR_CARRIAGE                        # load 0x0D carriage return into temporary
+    beq a0, t4, interpreter                     # ignore the character if it matches
+
     call uart_put                               # send the character to UART
 
 skip_send:
@@ -27,11 +34,6 @@ skip_send:
     li t0, CHAR_BACKSPACE                       # load backspace into temporary
     beq a0, t0, process_backspace               # process the backspace if it matches
 
-    li t0, CHAR_CARRIAGE                        # load carriage return into temporary
-    beq a0, t0, process_carriage                # process the carriage return if it matches
-
-    # TODO: check if character is printable
-
 interpreter_tib:
     # add the character to the TIB
     li t4, TIB_TOP                              # load TIB_TOP memory address
@@ -64,10 +66,6 @@ process_backspace:
 
     j interpreter           # return to the interpreter after erasing the character
 
-process_carriage:
-    li a0, CHAR_NEWLINE     # convert a carriage return to a newline
-    j interpreter_tib       # jump to add the character to the TIB
-
 .balign CELL
 replace_newline:
     li a0, CHAR_SPACE       # convert newline to a space
diff --git a/src/boards/longan-nano-lite/board.s b/src/boards/longan-nano-lite/board.s
new file mode 100644
index 0000000..28d5fb1
--- /dev/null
+++ b/src/boards/longan-nano-lite/board.s
@@ -0,0 +1,5 @@
+##
+# Longan Nano Lite
+##
+
+.equ RAM_SIZE, 1024 * 20                # 20 KiB
diff --git a/fiveforths.ld b/src/boards/longan-nano-lite/linker.ld
similarity index 96%
rename from fiveforths.ld
rename to src/boards/longan-nano-lite/linker.ld
index 1d3941f..68fb1a2 100644
--- a/fiveforths.ld
+++ b/src/boards/longan-nano-lite/linker.ld
@@ -1,3 +1,4 @@
+/* GD32VF103C8 */
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 64k
diff --git a/src/boards/longan-nano/board.s b/src/boards/longan-nano/board.s
new file mode 100644
index 0000000..c66d727
--- /dev/null
+++ b/src/boards/longan-nano/board.s
@@ -0,0 +1,5 @@
+##
+# Longan Nano
+##
+
+.equ RAM_SIZE, 1024 * 32                # 32 KiB
diff --git a/src/boards/longan-nano/linker.ld b/src/boards/longan-nano/linker.ld
new file mode 100644
index 0000000..24a9486
--- /dev/null
+++ b/src/boards/longan-nano/linker.ld
@@ -0,0 +1,22 @@
+/* GD32VF103CB */
+MEMORY
+{
+    FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 128k
+    RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 32k
+}
+
+/* The entry point is the reset handler */
+ENTRY(_start);
+
+SECTIONS {
+    __stacktop = ORIGIN(RAM) + LENGTH(RAM);
+
+    /* The program code and other data goes into FLASH */
+    .text :
+    {
+        . = ALIGN(4);
+        *(.text)           /* .text sections (code) */
+        *(.rodata)         /* .rodata sections (constants, strings, etc.) */
+    } >FLASH
+
+}
diff --git a/gd32vf103.s b/src/mcus/gd32vf103/mcu.s
similarity index 94%
rename from gd32vf103.s
rename to src/mcus/gd32vf103/mcu.s
index c53c828..100048f 100644
--- a/gd32vf103.s
+++ b/src/mcus/gd32vf103/mcu.s
@@ -2,6 +2,11 @@
 # GD32VF103
 ##
 
+.equ CELL, 4                            # 32-bits cell size
+.equ RAM_BASE, 0x20000000               # base address of RAM
+.equ STACK_SIZE, 256                    # 256 Bytes
+
+# UART
 .equ USART0_BASE_ADDRESS, 0x40013800
 .equ UART_RX_STATUS, 0x00       # USART status register offset (USART_STAT)
 .equ UART_RX_DATA, 0x04         # data register offset (USART_DATA)