We do not have an application note for 7455 but since you have EM75 working , 7455 will be much more simple. The main diferrence is that you do not need to set the MUX ID to the modem and driver via pack_wds_SetMuxID() and ioctl(QMI_SET_QMAP_xx). This is because, with the 74xx, each PDNs has distinct host device files. With the EM75, all PDNs are muxed over one qcqmiX device file.
The 7455 will create a RMNET device file for each PDN. For example, for 2 PDNs, 7455 will create /dev/qcqmi0 and /dev/qcqmi1. Pseudo code for multi - PDN
PDN 1, IPv4
- wds_ipv4fd_pdn1 = open(/dev/qcqmi0)
- ioctl(wds_ipv4fd_pdn1, QMI_GET_SERVICE_FILE_IOCTL, eWDS)
- pack_wds_SLQSSetIPFamilyPreference(IPv4). write(wds_ipv4fd_pdn1 )
- pack_wds_SLQSStartDataSession(). write(wds_ipv4fd_pdn1 )
PDN 2, IPv4
- wds_ipv4fd_pdn2 = open(/dev/qcqmi1)
- ioctl(wds_ipv4fd_pdn2, QMI_GET_SERVICE_FILE_IOCTL, eWDS)
- pack_wds_SLQSSetIPFamilyPreference(IPv4). write(wds_ipv4fd_pdn2 )
- pack_wds_SLQSStartDataSession(). write(wds_ipv4fd_pdn2 )
For IPv6 you would set the IP preference to IPv6 with 2 other FDs opened with the respective device file. You will then manage the FDs similar to EM75. Please refer “lite-connection-manager” for 74xx based data connection management.
The EM75(and WP76) can support multiple PDNs (we’ve tested upto 4) as QMAP can be handled in the host application. The 74xx modems can only support 2 PDNs as there is a USB interface limitation.
Hope the info is useful!