# An error occurs when writing to UART

**URL:** <https://forum.legato.io/t/an-error-occurs-when-writing-to-uart/6968>\
**Category:** Uncategorized\
**Created:** [December 9, 2025, 3:07pm UTC](https://forum.legato.io/t/an-error-occurs-when-writing-to-uart/6968 "2025-12-09T15:07:22Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![fujimitsu](https://avatars.discourse-cdn.com/v4/letter/f/46a35a/32.png) [@fujimitsu](https://forum.legato.io/u/fujimitsu)\
**Post date:** [December 9, 2025, 3:07pm UTC](https://forum.legato.io/t/an-error-occurs-when-writing-to-uart/6968/1 "2025-12-09T15:07:22Z")

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I am using WP7605. The OS versions are as follows:

- **Legato Version** : 21.05.2.rc2

- **Yocto Version** : SWI9X07Y\_03.01.07.00

- **OS Version** : Linux version 4.14.253

- **LK Version** : SWI9X07Y\_03.01.07.0

When I executed the `write` command on the UART, the following error occurred.  
Please tell me the cause and how to resolve it.

> [610.050803] msm\_hs\_set\_mctrl\_locked: UART 0, mctrl=0x0000, set\_dcd=1, set\_dsr=1, set\_ri=1 (0 is ON, 1 is OFF)  
> INFO | supervisor[1230]/supervisor T=main | proc.c proc\_SigChildHandler() 2094 | Process ‘mobileStation’ (PID: 1403) has exited with exit code 1.

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<div class="post-metadata">

**Author:** ![jyijyi](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.legato.io/jyijyi/32/822_2.png) [@jyijyi](https://forum.legato.io/u/jyijyi)\
**Post date:** [December 9, 2025, 3:20pm UTC](https://forum.legato.io/t/an-error-occurs-when-writing-to-uart/6968/2 "2025-12-09T15:20:30Z")

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You can refer to this application:

> [@\[WP7605\]\[SW\] Testing 8-wire UART1 by ioctrl( )](https://forum.legato.io/t/wp7605-sw-testing-8-wire-uart1-by-ioctrl/5533/4):
>
> We use this test app to test [UART\_Test1 (1).rar](https://forum.legato.io/uploads/short-url/vFbD9rHSFvq5gxhRMdeWnh45MbV.rar) (105.3 KB) BTW, do you have the test build for FW R17? If no, it is meaningless as the fix is on R17.