[BUG] ATMega2560 USART0 not working

[linguini1]

Description / Steps to reproduce the issue

The USART0 serial console does not work on ATMega2560 chips.

To reproduce:

$ ./tools/configure.sh arduino-mega2560:nsh
$ make -j

flash the image to the Arduino Mega2560 board.

Connect a USB-to-serial cable to pins 0 & 1 (RX0 & TX0) and GND. Observe no serial output at a baud rate of 38400, nor response to any input. Reboot the board with the serial monitor still connected and see the same thing again.

If you add avr_lowputc calls in the board initialization code, you'll see that the TX LED stays stuck on indefinitely.

On which OS does this issue occur?

[OS: Linux]

What is the version of your OS?

Linux 6.14.6-arch1-1 SMP PREEMPT_DYNAMIC x86_64 GNU/Linux

NuttX Version

master

Issue Architecture

[Arch: avr]

Issue Area

[Area: Specific Peripheral]

Host information

NuttX CFLAGS:
-fno-common
-Wall
-Wstrict-prototypes
-Wshadow
-Wundef
-Wno-attributes
-Wno-unknown-pragmas
-O2
-fno-strict-aliasing
-fomit-frame-pointer
-mmcu=atmega2560
-isystem /home/linguini/coding/nuttx-space/nuttx/include
-D__NuttX__
-DNDEBUG

NuttX CXXFLAGS:
-fno-common
-Wall
-Wshadow
-Wundef
-Wno-attributes
-Wno-unknown-pragmas
-nostdinc++
-fno-exceptions
-fcheck-new
-fno-rtti
-O2
-fno-strict-aliasing
-fomit-frame-pointer
-mmcu=atmega2560
-isystem /home/linguini/coding/nuttx-space/nuttx/include/cxx
-isystem /home/linguini/coding/nuttx-space/nuttx/include
-D__NuttX__
-DNDEBUG

NuttX LDFLAGS:
-mavr6
-Map=/home/linguini/coding/nuttx-space/nuttx/nuttx.map
-nostdlib

NuttX configuration options:
CONFIG_DEFAULT_SMALL=y
CONFIG_HOST_LINUX=y
CONFIG_APPS_DIR=../apps
CONFIG_BASE_DEFCONFIG=\arduino-mega2560:hello
CONFIG_BUILD_FLAT=y
CONFIG_INTELHEX_BINARY=y
CONFIG_OUTPUT_STRIP_PATHS=y
CONFIG_ARCH_NONE_DEBUG_H=y
CONFIG_FORTIFY_SOURCE=0
CONFIG_NDEBUG=y
CONFIG_DEBUG_ALERT=y
CONFIG_ARCH_HAVE_STACKCHECK=y
CONFIG_STACK_USAGE_WARNING=0
CONFIG_DEBUG_SYMBOLS=y
CONFIG_DEBUG_SYMBOLS_LEVEL=-g
CONFIG_ARCH_HAVE_CUSTOMOPT=y
CONFIG_DEBUG_FULLOPT=y
CONFIG_LTO_NONE=y
CONFIG_DEBUG_LINK_MAP=y
CONFIG_ARCH_AVR=y
CONFIG_ARCH=\avr
CONFIG_ARCH_FAMILY=\avr
CONFIG_ARCH_CHIP=\atmega
CONFIG_ARCH_CHIP_ATMEGA=y
CONFIG_ARCH_FAMILY_AVR=y
CONFIG_AVR_LINUXGCC_TOOLCHAIN=y
CONFIG_AVR_HAS_RAMPZ=y
CONFIG_ARCH_CHIP_ATMEGA2560=y
CONFIG_AVR_USART0=y
CONFIG_ARCH_TOOLCHAIN_GNU=y
CONFIG_ARCH_TOOLCHAIN_GCC=y
CONFIG_ARCH_NOINTC=y
CONFIG_ARCH_STACKDUMP=y
CONFIG_ARCH_STACKDUMP_MAX_LENGTH=0
CONFIG_BOARD_LOOPSPERMSEC=800
CONFIG_ARCH_HAVE_INTERRUPTSTACK=y
CONFIG_ARCH_INTERRUPTSTACK=0
CONFIG_BOOT_RUNFROMFLASH=y
CONFIG_RAM_START=0x800100
CONFIG_RAM_SIZE=8192
CONFIG_FLASH_START=0x0
CONFIG_FLASH_SIZE=0
CONFIG_ARCH_BOARD_ARDUINO_MEGA2560=y
CONFIG_ARCH_BOARD=\arduino-mega2560
CONFIG_BOARD_CRASHDUMP_NONE=y
CONFIG_BOARD_MEMORY_RANGE=\
CONFIG_DISABLE_OS_API=y
CONFIG_DISABLE_POSIX_TIMERS=y
CONFIG_DISABLE_PTHREAD=y
CONFIG_DISABLE_MQUEUE=y
CONFIG_DISABLE_MQUEUE_SYSV=y
CONFIG_DISABLE_ENVIRON=y
CONFIG_USEC_PER_TICK=10000
CONFIG_TIMER_ADJUST_USEC=0
CONFIG_START_YEAR=2011
CONFIG_START_MONTH=6
CONFIG_START_DAY=16
CONFIG_IRQ_NWORKS=8
CONFIG_IRQ_WORK_SECTION=\
CONFIG_IRQ_WORK_STACKSIZE=2048
CONFIG_INIT_ENTRY=y
CONFIG_INIT_ARGS=\
CONFIG_INIT_STACKSIZE=128
CONFIG_INIT_PRIORITY=100
CONFIG_INIT_ENTRYPOINT=\hello_main
CONFIG_INIT_ENTRYNAME=\hello_main
CONFIG_RR_INTERVAL=0
CONFIG_TASK_NAME_SIZE=0
CONFIG_SCHED_CPULOAD_NONE=y
CONFIG_SCHED_CPULOAD_TICKSPERSEC=100
CONFIG_SCHED_PROFILE_TICKSPERSEC=1000
CONFIG_SCHED_STACK_RECORD=0
CONFIG_DEV_CONSOLE=y
CONFIG_NFILE_DESCRIPTORS_PER_BLOCK=4
CONFIG_SIG_PREALLOC_ACTIONS=4
CONFIG_SIG_ALLOC_ACTIONS=1
CONFIG_SIG_PREALLOC_IRQ_ACTIONS=4
CONFIG_DEFAULT_TASK_STACKSIZE=2048
CONFIG_IDLETHREAD_STACKSIZE=128
CONFIG_PTHREAD_STACK_MIN=128
CONFIG_PTHREAD_STACK_DEFAULT=128
CONFIG_PID_INITIAL_COUNT=8
CONFIG_DEV_OPTEE_NONE=y
CONFIG_ARCH_HAVE_SERIAL_TERMIOS=y
CONFIG_SERIAL=y
CONFIG_SERIAL_CONSOLE=y
CONFIG_MCU_SERIAL=y
CONFIG_STANDARD_SERIAL=y
CONFIG_SERIAL_NPOLLWAITERS=4
CONFIG_USART0_SERIAL_CONSOLE=y
CONFIG_USART0_SERIALDRIVER=y
CONFIG_USART0_RXBUFSIZE=256
CONFIG_USART0_TXBUFSIZE=256
CONFIG_USART0_BAUD=38400
CONFIG_USART0_BITS=8
CONFIG_USART0_PARITY=0
CONFIG_USART0_2STOP=0
CONFIG_SYSLOG=y
CONFIG_SYSLOG_DEFAULT_MASK=0xff
CONFIG_SYSLOG_CRLF=y
CONFIG_SYSLOG_MAX_CHANNELS=1
CONFIG_SYSLOG_DEVPATH=/dev/ttyS1
CONFIG_SYSLOG_DEFAULT=y
CONFIG_CONSOLE_SYSLOG=y
CONFIG_DISABLE_MOUNTPOINT=y
CONFIG_FS_NEPOLL_DESCRIPTORS=8
CONFIG_FS_LOCK_BUCKET_SIZE=0
CONFIG_DISABLE_PSEUDOFS_OPERATIONS=y
CONFIG_SENDFILE_BUFSIZE=512
CONFIG_FS_BACKTRACE=0
CONFIG_NXFONTS_PACKEDMSFIRST=y
CONFIG_MM_DEFAULT_MANAGER=y
CONFIG_MM_DEFAULT_ALIGNMENT=8
CONFIG_MM_SMALL=y
CONFIG_MM_REGIONS=1
CONFIG_MM_MAP_COUNT_MAX=1024
CONFIG_MM_BACKTRACE=-1
CONFIG_MM_FREE_DELAYCOUNT_MAX=0
CONFIG_MM_HEAP_BIGGEST_COUNT=30
CONFIG_MM_HEAP_MEMPOOL_THRESHOLD=-1
CONFIG_BINFMT_DISABLE=y
CONFIG_BINFMT_ELF_RELOCATABLE=y
CONFIG_STDIO_BUFFER_SIZE=0
CONFIG_STDIO_LINEBUFFER=y
CONFIG_NUNGET_CHARS=0
CONFIG_ARCH_LOWPUTC=y
CONFIG_LIBC_RAND_ORDER=1
CONFIG_LIBC_HOMEDIR=/
CONFIG_LIBC_TMPDIR=/tmp
CONFIG_LIBC_MAX_TMPFILE=32
CONFIG_LIBC_MAX_EXITFUNS=0
CONFIG_POSIX_SPAWN_DEFAULT_STACKSIZE=2048
CONFIG_LIBC_HOSTNAME=\
CONFIG_LIBC_OPEN_MAX=256
CONFIG_NAME_MAX=32
CONFIG_PATH_MAX=256
CONFIG_LINE_MAX=64
CONFIG_LIBC_STRSIGNAL=y
CONFIG_LIBC_STRSIGNAL_SHORT=y
CONFIG_TLS_TASK_NELEM=0
CONFIG_TLS_NCLEANUP=0
CONFIG_LIBC_GAISTRERROR_ERRNUM=y
CONFIG_LIBC_FTOK_VFS_PATH=/var/ftok
CONFIG_LIBC_MEMFD_ERROR=y
CONFIG_LIBC_MUTEX_BACKTRACE=0
CONFIG_STREAM_OUT_BUFFER_SIZE=64
CONFIG_STREAM_HEXDUMP_BUFFER_SIZE=128
CONFIG_STREAM_BASE64_BUFFER_SIZE=128
CONFIG_LIBM_NONE=y
CONFIG_BUILTIN_TOOLCHAIN=y
CONFIG_COVERAGE_NONE=y
CONFIG_COVERAGE_DEFAULT_PREFIX_STRIP=\99
CONFIG_COVERAGE_DEFAULT_PREFIX=/data
CONFIG_PROFILE_NONE=y
CONFIG_EXAMPLES_HELLO=y
CONFIG_EXAMPLES_HELLO_PROGNAME=\hello
CONFIG_EXAMPLES_HELLO_PRIORITY=100
CONFIG_EXAMPLES_HELLO_STACKSIZE=2048

Host system OS:
Linux pastabox 6.14.6-arch1-1 #1 SMP PREEMPT_DYNAMIC Fri 09 May 2025 17:36:18 +0000 x86_64

Host system PATH:
/home/linguini/.cargo/bin
/sbin
/bin
/usr/local/sbin
/usr/local/bin
/usr/sbin
/usr/bin
/opt/cuda/bin
/opt/cuda/nsight_compute
/opt/cuda/nsight_systems/bin
/usr/lib/jvm/default/bin
/usr/bin/site_perl
/usr/bin/vendor_perl
/usr/bin/core_perl
/opt/rocm/bin
/usr/lib/rustup/bin

Verification

• I have verified before submitting the report.

[linguini1]

I've found that the board seems to crash at the kumm_initialize() call in nx_start, and then restarts from the beginning forever. The crash has been narrowed down to mm_initialize_pool("Umem", ...) in umm_initialize of file mm/umm_heap/umm_initialize.c. Continuing to debug what the issue is here.

[linguini1]

Using up_putc statements I have narrowed down the issue to a failing DEBUASSERT(MM_NODE_IS_FREE(node)) in mm/mm_heap/mm.h's definition of mm_addfreechunk.

[linguini1]

With the following modifications:

static inline_function void mm_addfreechunk(FAR struct mm_heap_s *heap,
                                            FAR struct mm_freenode_s *node)
{
  FAR struct mm_freenode_s *next;
  FAR struct mm_freenode_s *prev;
  size_t nodesize = MM_SIZEOF_NODE(node);
  int ndx;

    if (!(nodesize >= MM_MIN_CHUNK)){
        up_putc('1');
    }

    if (!(MM_NODE_IS_FREE(node))){
        up_putc('2');
    }

    up_putc('a');
  DEBUGASSERT(nodesize >= MM_MIN_CHUNK);
    up_putc('b');
  DEBUGASSERT(MM_NODE_IS_FREE(node));
    up_putc('c');

  /* ... */

I see this output (repeats forever as it spuriously reboots):

12a12a12a12a

[linguini1]

I see this output:

1a1a1a

with these configuration settings:

# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set
CONFIG_ARCH="avr"
CONFIG_ARCH_AVR=y
CONFIG_ARCH_BOARD="arduino-mega2560"
CONFIG_ARCH_BOARD_ARDUINO_MEGA2560=y
CONFIG_ARCH_CHIP="atmega"
CONFIG_ARCH_CHIP_ATMEGA2560=y
CONFIG_ARCH_CHIP_ATMEGA=y
CONFIG_ARCH_STACKDUMP=y
CONFIG_AVR_LINUXGCC_TOOLCHAIN=y
CONFIG_AVR_USART0=y
CONFIG_BOARD_LOOPSPERMSEC=800
CONFIG_DEBUG_ASSERTIONS=y
CONFIG_DEBUG_ASSERTIONS_FILENAME=y
CONFIG_DEBUG_FEATURES=y
CONFIG_DEBUG_FULLOPT=y
CONFIG_DEBUG_SYMBOLS=y
CONFIG_DEFAULT_SMALL=y
CONFIG_DISABLE_MOUNTPOINT=y
CONFIG_IDLETHREAD_STACKSIZE=128
CONFIG_INIT_ENTRYPOINT="nsh_main"
CONFIG_INIT_STACKSIZE=768
CONFIG_INTELHEX_BINARY=y
CONFIG_NDEBUG=y
CONFIG_NFILE_DESCRIPTORS_PER_BLOCK=4
CONFIG_NUNGET_CHARS=0
CONFIG_POSIX_SPAWN_DEFAULT_STACKSIZE=768
CONFIG_PTHREAD_STACK_DEFAULT=128
CONFIG_PTHREAD_STACK_MIN=128
CONFIG_RAM_SIZE=8192
CONFIG_RAM_START=0x800100
CONFIG_START_DAY=16
CONFIG_START_MONTH=6
CONFIG_START_YEAR=2011
CONFIG_STDIO_BUFFER_SIZE=0
CONFIG_SYSTEM_NSH=y
CONFIG_TASK_NAME_SIZE=0
CONFIG_USART0_BAUD=38400
CONFIG_USART0_SERIAL_CONSOLE=y

[linguini1]

It appears that the nodesize ends up being equal to 0, while MM_MIN_CHUNK is equal to 8.

[linguini1]

I can't seem to get a working version of arduino-mega2560:nsh or arduino-mega2560:hello as far back as releases/11.0

[acassis]

@linguini1 I'm copying KR message here (since he doesn't use github)

I found some time to look into this and I believe I found the reason for
"If you add avr_lowputc calls in the board initialization code, you'll
see that the TX LED stays stuck on indefinitely."

Provided the board initialization code that sentence is talking about is
atmega_boardinitialize() in avr_boot.c, then avr_lowputc() likely does
not work because of the configuration used. According to #16444, the
configuration has:

CONFIG_DEV_CONSOLE=y
CONFIG_CONSOLE_SYSLOG=y

These two are processed in src/atmega/atmega_config.h

#ifndef CONFIG_DEV_CONSOLE
#  undef  USE_SERIALDRIVER
#  undef  USE_EARLYSERIALINIT
#else
#  if defined(CONFIG_CONSOLE_SYSLOG)
#    undef  USE_SERIALDRIVER
#    undef  USE_EARLYSERIALINIT
#  elif defined(HAVE_USART_DEVICE)
#    define USE_SERIALDRIVER 1
#    define USE_EARLYSERIALINIT 1
#  else
#    undef  USE_SERIALDRIVER
#    undef  USE_EARLYSERIALINIT
#  endif
#endif

With the configuration above, the outer ifndef is not true and first if
defined in else block is true, which results into:

undef  USE_SERIALDRIVER
undef  USE_EARLYSERIALINIT

Since CONFIG_STANDARD_SERIAL is also set, the undef of USE_SERIALDRIVER
is reverted by define USE_SERIALDRIVER 1 later. However,
USE_EARLYSERIALINIT remains unset.

This causes avr_earlyserialinit() to not be built nor called from
avr_lowinit(). Serial port peripheral is therefore not initialized yet
when atmega_boardinitialize() is called. I don't know what exactly
happens when you attempt to transmit data with the port not enabled but
my guess would be that "transmit data register empty" status flag is
just never cleared and the program ends up in a loop waiting for that to
happen.


Other than that - I recently tested NSH on mega1284p-xplained (well, a
breadboard with the chip stuck in it actually) and it worked for me. As
far as I can see, all AtMega devices use the same code for managing
serial ports so it should work out of the box.

Someone somewhere in some forum on the net has or had a footer in his
posts saying something along the lines of that non-functional serial
port is 99% mismatching baud rates, might be worth a re-check.

As for the PR itself (copying from e-mail mentioned at the beginning) -
I would recommend trying to use KEEP(*(.vectors)) as seen in
boards/avr/avrdx/breadxavr/scripts/breadxavr.ld - the default config
should then not need the "# CONFIG_DEBUG_OPT_UNUSED_SECTIONS is not set"
line.

[linguini1]

Going to post a link to the email thread here for record-keeping purposes, since KR seems to be more reachable there: https://lists.apache.org/thread/qlg38b9s1fzlyfscpldbfztcvc94fr2j

[linguini1]

It does seem to be a memory issue as suggested by KR, attempting to print a string like so:

static char static_str[] = "hello from static";
for (int i = 0; i < sizeof(static_str) / sizeof(char); i++)
{
  up_putc(static_str[i]);
}

or like so

char stack_str[] = "hello from stack";
for (int i = 0; i < sizeof(stack_str) / sizeof(char); i++)
  {
    up_putc(stack_str[i]);
  }

Fails. In fact, I can see it run into some string in memory and start printing that forever instead:

signal/sig_actionsignal/sig_actionsignal/sig_actionsignal/sig_actionsignal/sig_actionsignal/sig_actionsignal/sig_actionsignal/sig_...

[linguini1]

If I change the linker script such that:

    .data            :
    {
        _sdata = ABSOLUTE(.);
        *(.rodata .rodata.*)
        *(.data .data.*)
        *(.gnu.linkonce.d.*)
        CONSTRUCTORS
        _edata = ABSOLUTE(.);
    } > sram AT > flash

    _eronly = LOADADDR(.data);

diff --git a/boards/avr/atmega/arduino-mega2560/scripts/flash.ld b/boards/avr/atmega/arduino-mega2560/scripts/flash.ld
index f365646dfa..73a62017ed 100644
--- a/boards/avr/atmega/arduino-mega2560/scripts/flash.ld
+++ b/boards/avr/atmega/arduino-mega2560/scripts/flash.ld
@@ -122,7 +122,6 @@ SECTIONS
         _etext = . ;
     } > flash
 
-    _eronly = ABSOLUTE(.);
 
     .data            :
     {
@@ -134,6 +133,8 @@ SECTIONS
         _edata = ABSOLUTE(.);
     } > sram AT > flash
 
+    _eronly = LOADADDR(.data);
+
     .bss            :
     {
         _sbss = ABSOLUTE(.);

I am able to boot into NSH. It appears the initializer data for the variables loaded to SRAM from FLASH is not actually getting stored in flash in the image.