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arch/sim: Add PTY mode for simulated UART

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The simulated UART driver currently opens the host path configured by
CONFIG_SIM_UARTx_NAME directly. This requires the host-side serial endpoint
to exist before NuttX opens the UART, so users and CI jobs need an external
setup step such as socat to create a PTY pair. It also means the host
endpoint path is effectively a build-time choice: changing the host device
path requires changing configuration and rebuilding, which is inconvenient
for tests that allocate a fresh PTY path on each run.

Add CONFIG_SIM_UART_PTY for Linux sim builds. When enabled, non-console
simulated UART ports allocate a host pseudoterminal from /dev/ptmx, put the
host master side in raw mode, and print the host slave path when the NuttX
UART is opened. The NuttX-side device name remains CONFIG_SIM_UARTx_NAME,
for example /dev/ttySIM0, so applications continue to use the normal NuttX
serial API.

Keep the option disabled by default so existing configurations still open
the configured host path directly. Console UART handling is also left on the
existing host-open path.

Also make host_uart_checkin() and host_uart_checkout() check the actual
POLLIN/POLLOUT bits returned by poll(). This avoids treating error-only or
unrelated poll events as readable or writable serial readiness.

The main benefit is simpler and more deterministic simulator integration: a
simulated UART can expose a real host-visible /dev/pts/N endpoint by itself,
without pre-creating a matching host device and without rebuilding NuttX
when the host PTY path changes. This is useful for host-side test scripts
and external protocol tools while keeping application code on the standard
NuttX UART interface.

Companion apps-side test branch:

  https://github.com/LingaoM/nuttx-apps/tree/sim_uart_tester

Testing:

  Host:

    Ubuntu 22.04 x86_64

  Board/config:

    sim:nsh

  Apps test code:

    https://github.com/LingaoM/nuttx-apps/tree/sim_uart_tester

  Common test configuration:

    CONFIG_NSH_BUILTIN_APPS=y
    CONFIG_EXAMPLES_HELLO=y
    CONFIG_SIM_UART_NUMBER=1
    CONFIG_SIM_UART0_NAME="/dev/ttySIM0"
    CONFIG_SIM_UART_PTY=y

  DMA-mode build and test:

    1. Configure sim:nsh with the companion apps tree:

         ./tools/configure.sh -a ../nuttx-apps sim:nsh

    2. Enable the common test configuration above and keep DMA enabled:

         CONFIG_SIM_UART_DMA=y
         CONFIG_SERIAL_TXDMA=y
         CONFIG_SERIAL_RXDMA=y

    3. Build:

         make clean
         make -j16

    4. Start NuttX:

         ./nuttx

    5. In NSH, run the hello test app:

         nsh> hello
         /dev/ttySIM0 connected to pseudotty: /dev/pts/73

    6. In another terminal, run the host-side tester from the companion apps
       branch with the printed PTY path:

         cd ../nuttx-apps
         ./examples/hello/test_sim_uart_pty.py /dev/pts/73

    7. The host-side tester sends 32768 bytes from the host to NuttX and
       receives 49152 bytes from NuttX to the host. The payload includes
       non-text binary bytes. Both sides validate deterministic payload
       contents and checksums, then exchange an ACK.

    8. Observed host-side output:

         HOST_OPEN: /dev/pts/73
         HOST_TX: 32768 bytes checksum=0x1f9989f4
         HOST_RX: 49152 bytes checksum=0x06a45c69
         HOST_TX: ACK
         TEST PASSED

    9. Observed NuttX output:

         sim_uart_pty_test: binary RX 32768 TX 49152 passed

  Non-DMA build and test:

    1. Disable DMA for the same sim:nsh configuration:

         # CONFIG_SIM_UART_DMA is not set
         # CONFIG_SERIAL_TXDMA is not set
         # CONFIG_SERIAL_RXDMA is not set

    2. Refresh the configuration and rebuild. On this host, the installed
       Python olddefconfig shim is broken, so I refreshed Kconfig directly
       with kconfig-conf and the same environment that the NuttX Makefile
       passes to Kconfig:

         APPSDIR=/mnt/ssd/code/code/nuttx-apps \
         APPSBINDIR=/mnt/ssd/code/code/nuttx-apps \
         BINDIR=/mnt/ssd/code/code/nuttx \
         EXTERNALDIR=/mnt/ssd/code/code/nuttx/dummy \
           kconfig-conf --olddefconfig Kconfig

         make clean
         make -j16

    3. Repeated the same runtime steps as the DMA test:

         ./nuttx
         nsh> hello
         cd ../nuttx-apps
         ./examples/hello/test_sim_uart_pty.py /dev/pts/73

    4. Observed the same successful binary transfer result:

         HOST_TX: 32768 bytes checksum=0x1f9989f4
         HOST_RX: 49152 bytes checksum=0x06a45c69
         HOST_TX: ACK
         TEST PASSED
         sim_uart_pty_test: binary RX 32768 TX 49152 passed

  After the non-DMA test, I restored the default DMA configuration, rebuilt,
  and reran the same binary PTY test successfully so the final local build
  state was back on CONFIG_SIM_UART_DMA=y.

Assisted-by: Claude:Claude-Fable-5
Signed-off-by: Lingao Meng <menglingao@xiaomi.com>
This commit is contained in:
Lingao Meng 2026-07-24 14:13:06 +08:00 • committed by Xiang Xiao
parent 88e7b37328
commit aa3157e234
6 changed files with 141 additions and 19 deletions
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15
Documentation/platforms/sim/sim/boards/sim/index.rst
View file

@ -2186,10 +2186,23 @@ nxscope
Configuration demonstrating NxScope stream over simulated UART interface.
The simulated UART must be created on host before running NuttX::
If ``CONFIG_SIM_UART_PTY`` is disabled, the simulated UART peer must be
created on the host before running NuttX::
socat PTY,link=/dev/ttySIM0 PTY,link=/dev/ttyNX0
In that mode ``CONFIG_SIM_UART0_NAME`` is both the NuttX device name and
the host path that the sim UART backend opens. This works when the host
path is stable, but it is inconvenient for automated tests and generated
PTYs: the peer device must exist before the UART is opened, and changing
the host path requires changing the NuttX configuration.
If ``CONFIG_SIM_UART_PTY`` is enabled, NuttX creates the host
pseudoterminal when the simulated UART is opened and prints the host
PTY slave path. The configured ``SIM_UARTx_NAME`` remains the NuttX
device name, while the host PTY path is allocated at runtime and can be
passed to the external simulator or test program.
See :doc:`/applications/examples/nxscope/index` and
:doc:`/applications/logging/nxscope/index` for more details.

60
arch/sim/Kconfig
View file

@ -774,6 +774,11 @@ config SIM_UART_NUMBER
Anything sent to the one of these ports will be relayed
automatically to the other, and vice-versa.
If SIM_UART_PTY is enabled, NuttX creates the simulated
host pseudoterminal itself. In that mode SIM_UARTx_NAME is
only the NuttX device name, and the host pseudoterminal path
is printed when the port is opened.
config SIM_UART_BUFFER_SIZE
int "UART buffer size"
default 256
@ -784,16 +789,41 @@ config SIM_UART_BUFFER_SIZE
Note that all ports will have the same buffer size.
config SIM_UART_PTY
bool "Create host pseudoterminals for simulated UART ports"
default n
depends on HOST_LINUX && SIM_UART_NUMBER >= 1
---help---
Open a new host pseudoterminal for each simulated UART
instead of opening an existing host serial device. The
UART remains registered in NuttX using SIM_UARTx_NAME, and
the host PTY slave path is printed when the port is opened.
The existing behavior requires the host endpoint named by
SIM_UARTx_NAME to exist before the simulated UART is opened.
This makes automated tests awkward when the peer endpoint is
a generated PTY with a host-dependent path, because the host
path must be prepared up front and encoded in the NuttX
configuration. With this option enabled, the sim UART
backend owns the host PTY allocation and reports the actual
slave path at runtime, while keeping the NuttX device name
stable for applications.
If disabled, SIM UART keeps the existing behavior and opens
the host device path specified by SIM_UARTx_NAME directly.
config SIM_UART0_NAME
string "UART port 0 name"
default "/dev/ttySIM0"
depends on SIM_UART_NUMBER >= 1
---help---
This is the name of the simulated UART port.
The port will be mounted in NuttX under this name.
The port will be registered in NuttX under this name.
A UART port must also exist on the host system
with the exact same name specified here.
If SIM_UART_PTY is disabled, a UART port must also exist on
the host system with the exact same name specified here. If
SIM_UART_PTY is enabled, the host pseudoterminal is allocated
automatically and printed when this port is opened.
config SIM_UART1_NAME
string "UART port 1 name"
@ -801,10 +831,12 @@ config SIM_UART1_NAME
depends on SIM_UART_NUMBER >= 2
---help---
This is the name of the simulated UART port.
The port will be mounted in NuttX under this name.
The port will be registered in NuttX under this name.
A UART port must also exist on the host system
with the exact same name specified here.
If SIM_UART_PTY is disabled, a UART port must also exist on
the host system with the exact same name specified here. If
SIM_UART_PTY is enabled, the host pseudoterminal is allocated
automatically and printed when this port is opened.
config SIM_UART2_NAME
string "UART port 2 name"
@ -812,10 +844,12 @@ config SIM_UART2_NAME
depends on SIM_UART_NUMBER >= 3
---help---
This is the name of the simulated UART port.
The port will be mounted in NuttX under this name.
The port will be registered in NuttX under this name.
A UART port must also exist on the host system
with the exact same name specified here.
If SIM_UART_PTY is disabled, a UART port must also exist on
the host system with the exact same name specified here. If
SIM_UART_PTY is enabled, the host pseudoterminal is allocated
automatically and printed when this port is opened.
config SIM_UART3_NAME
string "UART port 3 name"
@ -823,10 +857,12 @@ config SIM_UART3_NAME
depends on SIM_UART_NUMBER >= 4
---help---
This is the name of the simulated UART port.
The port will be mounted in NuttX under this name.
The port will be registered in NuttX under this name.
A UART port must also exist on the host system
with the exact same name specified here.
If SIM_UART_PTY is disabled, a UART port must also exist on
the host system with the exact same name specified here. If
SIM_UART_PTY is enabled, the host pseudoterminal is allocated
automatically and printed when this port is opened.
config SIM_RAM_UART
bool "SIM RAM UART Device"

57
arch/sim/src/sim/posix/sim_hostuart.c
View file

@ -24,6 +24,7 @@
* Included Files
****************************************************************************/
#include <sys/ioctl.h>
#include <fcntl.h>
#include <stdbool.h>
#include <unistd.h>
@ -130,6 +131,58 @@ int host_uart_open(const char *pathname)
return fd;
}
/****************************************************************************
* Name: host_uart_openpty
****************************************************************************/
int host_uart_openpty(const char *name)
{
#ifdef CONFIG_HOST_LINUX
unsigned int ptyno;
int lock = 0;
int oflags;
int ret;
int fd;
oflags = O_RDWR | O_NOCTTY | O_NONBLOCK;
#ifdef O_CLOEXEC
oflags |= O_CLOEXEC;
#endif
fd = open("/dev/ptmx", oflags);
if (fd < 0)
{
return -errno;
}
ret = ioctl(fd, TIOCGPTN, &ptyno);
if (ret < 0)
{
ret = -errno;
goto errout;
}
ret = ioctl(fd, TIOCSPTLCK, &lock);
if (ret < 0)
{
ret = -errno;
goto errout;
}
setrawmode(fd);
printf("%s connected to pseudotty: /dev/pts/%u\n", name, ptyno);
return fd;
errout:
close(fd);
return ret;
#else
(void)name;
return -ENOSYS;
#endif
}
/****************************************************************************
* Name: host_uart_close
****************************************************************************/
@ -229,7 +282,7 @@ bool host_uart_checkin(int fd)
pfd.fd = fd;
pfd.events = POLLIN;
return poll(&pfd, 1, 0) == 1;
return poll(&pfd, 1, 0) == 1 && (pfd.revents & POLLIN) != 0;
}
/****************************************************************************
@ -242,7 +295,7 @@ bool host_uart_checkout(int fd)
pfd.fd = fd;
pfd.events = POLLOUT;
return poll(&pfd, 1, 0) == 1;
return poll(&pfd, 1, 0) == 1 && (pfd.revents & POLLOUT) != 0;
}
/****************************************************************************

1
arch/sim/src/sim/sim_internal.h
View file

@ -284,6 +284,7 @@ void sim_uartinit(void);
void host_uart_start(void);
int host_uart_open(const char *pathname);
int host_uart_openpty(const char *name);
void host_uart_close(int fd);
int host_uart_puts(int fd, const char *buf, size_t size);
int host_uart_gets(int fd, char *buf, size_t size);

17
arch/sim/src/sim/sim_uart.c
View file

@ -307,9 +307,8 @@ static void uart_nputs(int fd, const char *buf, size_t size)
* Name: tty_setup
*
* Description:
* Configure the UART baud, bits, parity, fifos, etc. This
* method is called the first time that the serial port is
* opened.
* Open and configure the host endpoint for the simulated UART.
* This method is called the first time that the serial port is opened.
*
****************************************************************************/
@ -317,7 +316,17 @@ static int tty_setup(struct uart_dev_s *dev)
{
struct tty_priv_s *priv = dev->priv;
priv->fd = host_uart_open(priv->path);
#ifdef CONFIG_SIM_UART_PTY
if (!dev->isconsole)
{
priv->fd = host_uart_openpty(priv->path);
}
else
#endif
{
priv->fd = host_uart_open(priv->path);
}
return priv->fd;
}

10
arch/sim/src/sim/win/sim_hostuart.c
View file

@ -74,6 +74,16 @@ int host_uart_open(const char *pathname)
return -ENOSYS;
}
/****************************************************************************
* Name: host_uart_openpty
****************************************************************************/
int host_uart_openpty(const char *name)
{
(void)name;
return -ENOSYS;
}
/****************************************************************************
* Name: host_uart_close
****************************************************************************/