Cellular: For ublox modem, read '@' char first then send data.

[mudassar-ublox]

Summary of changes

Reading @ before sending data. As for Ublox modem: After the command is sent, the user waits for the @ prompt and after the @ prompt reception, wait for a minimum of 50 ms before sending data.

Impact of changes

Migration actions required

Documentation

---

Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

---

Reviewers

---

[ciarmcom]

@mudassar-ublox, thank you for your changes.
@ARMmbed/mbed-os-wan @ARMmbed/mbed-os-maintainers please review.

[pilotak]

I got a NSAPI_ERROR_TIMEOUT when running under this patch. Maybe this is because of the new lines <cr> and <ln>?

[00080921ms][INFO][CELL]: AT RX (26): AT+USOCO=0,"52.215.34.155"
[00080929ms][INFO][CELL]: AT RX ( 3): ,7<cr>
[00081422ms][INFO][CELL]: AT RX ( 1): <cr>
[00081427ms][INFO][CELL]: AT RX ( 2): <ln>O
[00081432ms][INFO][CELL]: AT RX ( 3): K<cr><ln>
connected
[00081439ms][INFO][CELL]: AT TX ( 9): AT+USOWR=
[00081444ms][INFO][CELL]: AT TX ( 1): 0
[00081449ms][INFO][CELL]: AT TX ( 1): ,
[00081454ms][INFO][CELL]: AT TX ( 1): 4
[00081459ms][INFO][CELL]: AT TX ( 1): <cr>
[00081514ms][INFO][CELL]: AT RX (16): AT+USOWR=0,4<cr><cr><ln>@
[00081621ms][ERR ][CELL]: Socket 0 sendto 52.215.34.155 error -3019
Socket send FAILED: -3019

[mudassar-ublox]

@pilotak, Seeing that your echo is on thats why you are receiving echo back of command AT+USOWR=0,4 along with @ result in failure.

[pilotak]

i'm using default init() which has echo off

mbed-os/features/cellular/framework/targets/UBLOX/AT/UBLOX_AT.cpp

Line 149 in 5969fdf

_at.at_cmd_discard("E0", ""); // echo off

or do you mean that i can't have a "cellular.debug-at": true?

[0xc0170]

@mudassar-ublox Please fix astyle

Pull request has been modified.

[mudassar-ublox]

@pilotak please check now, PR updated and @0xc0170 also astyle fixed.

[pilotak]

perfect, thank you

[mudassar-ublox]

perfect, thank you

Welcome, can you please close the issue #12461. Thanks

[0xc0170]

CI started

[mbed-ci]

Test run: FAILED

Summary: 1 of 7 test jobs failed
Build number : 1
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_cloud-client-pytest