Let’s focus on setting DTR pin in mangOH green board (CN600 connector pin 11) first with my yocto image.
Here I have tried the following:
root@swi-mdm9x28-wp:~# cm info
Device: WP7609
IMEI: 359782080100373
IMEISV: 6
FSN: WA803370311610
Firmware Version: SWI9X07Y_02.25.02.01 000000 jenkins 2019/01/30 08:13:05
Bootloader Version: SWI9X07Y_02.25.02.01 000000 jenkins 2019/01/30 08:13:05
MCU Version:
PRI Part Number (PN): 9908102
PRI Revision: 001.000
Carrier PRI Name: GENERIC
Carrier PRI Revision: 002.056_000
SKU: 1103843
Last Reset Cause: Power Down
Resets Count: Expected: 10 Unexpected: 1
root@swi-mdm9x28-wp:~# legato version
18.10.3_0b50331a9f4d0ecc0fd816c2a1300436
root@swi-mdm9x28-wp:~# microcom /dev/ttyAT
ati3
Manufacturer: Sierra Wireless, Incorporated
Model: WP7609
Revision: SWI9X07Y_02.25.02.01 000000 jenkins 2019/01/30 08:13:05
IMEI: 359782080100373
IMEI SV: 6
FSN: WA803370311610
+GCAP: +CGSM
OK
ati8
Legato Ver: 18.10.3_0b50331a9f4d0ecc0fd816c2a1300436
Yocto Ver: SWI9X07Y_02.25.02.01 2019-08-08_12:54:14
OS Ver: Linux version 3.18.122 (owner@CNHKG-EX-001367) (gcc version 6.2.0 (GCC) ) #2 PREEMPT Thu Aug 8 12:56:18 HKT 2019
LK Ver: SWI9X07Y_02.25.02.01
RootFS Ver: SWI9X07Y_02.25.02.01 2019-08-08_12:54:14
UserFS Ver: unknown
MCU Ver: unknown
OK
root@swi-mdm9x28-wp:~# echo 101 > /sys/class/gpio/export
root@swi-mdm9x28-wp:~# echo out > /sys/class/gpio/gpio101/direction
root@swi-mdm9x28-wp:~# echo 1 > /sys/class/gpio/gpio101/value
root@swi-mdm9x28-wp:~# echo 0 > /sys/class/gpio/gpio101/value
I measure DTR pin in mangOH green board (CN600 connector pin 11), the status will change.
If you cannot make this work, probably there is hardware problem on your side.