Mbed-os: compiler warnings on several NXP targets

[bmcdonnell-ionx]

Description

• Type: Bug
• Priority: Minor

---

Bug

Target
Many NXP targets.

mbed-os sha:
6ff720302 (tag: mbed-os-5.8.0-rc1, origin/mbed-os-5.8, mbed-os-5.8) Add Mbed version block for new minor release.

Description

For many NXP targets (e.g. LPC4088), the serial_format() function in serial_api.c doesn't handle invalid values of the SerialParity parameter correctly, leading to a compiler warning:

../mbed-os/targets/TARGET_NXP/TARGET_LPC408X/TARGET_LPC4088/serial_api.c: In function 'serial_format':
../mbed-os/targets/TARGET_NXP/TARGET_LPC408X/TARGET_LPC4088/serial_api.c:236:43: warning: 'parity_select' may be used uninitialized in this function [-Wmaybe-uninitialized]
                    | parity_select        << 4;
                      ~~~~~~~~~~~~~~~~~~~~~^~~~
../mbed-os/targets/TARGET_NXP/TARGET_LPC408X/TARGET_LPC4088/serial_api.c:235:43: warning: 'parity_enable' may be used uninitialized in this function [-Wmaybe-uninitialized]
                    | parity_enable        << 3
                      ~~~~~~~~~~~~~~~~~~~~~^~~~

Also, the handling is not uniform. Various observed correct handling methods include:

• return on the default switch case
• set default values in the default case
• set default values before the switch statement

To see all the variants (good and bad), you can do this at a POSIX command line:

for f in `find targets/TARGET_NXP -name serial_api.c`; do echo $f; awk '/void +serial_format/,/^\}/' $f; echo; done | less

Suggested changes

Choose a method and apply it uniformly to all. Also make the MBED_ASSERTs consistent (add to or remove from all).

[0xc0170]

@ARMmbed/team-nxp please review

[ciarmcom]

ARM Internal Ref: MBOTRIAGE-234

[maclobdell]

@mmahadevan108 Any update on this?

[mmahadevan108]

PR https://github.com/ARMmbed/mbed-os/pull/8010 should fix this issue.