How to solve MT7620A / MiWifi R1c with PandoraBox / Openwrt - Cannot install IPK - solve incompatible with the architectures configured

Problem: I cannot install ipk file on my MT7620A router.

The MT7620A CPU is MIPS 24KEc architecture:
#cat /proc/cpuinfo
system type             : MediaTek MT7620
machine                 : Xiaomi mini Board
processor               : 0
cpu model               : MIPS 24KEc V5.0
BogoMIPS                : 385.84
wait instruction        : yes
microsecond timers      : yes
tlb_entries             : 32
extra interrupt vector  : yes
hardware watchpoint     : yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa                     : mips1 mips2 mips32r2
ASEs implemented        : mips16 dsp
shadow register sets    : 1
kscratch registers      : 0
core                    : 0
VCED exceptions         : not available
VCEI exceptions         : not available

 It should be able to install IPK which is compiled for this platform.  However, when I try to install ipk, I got "incompatible with the architecture" error:

#opkg install xxxx_ramips_24kec.ipk
Unknown package 'xxxx'.
Collected errors:
 * pkg_hash_fetch_best_installation_candidate: Packages for xxxx found, but incompatible with the architectures configured
 * opkg_install_cmd: Cannot install package xxxxxx.

Then I further double check the opkg supported architecture:

#opkg print-architecture
arch all 1
arch noarch 1
arch ralink 10

It lacks support of mips.  Therefore, I need to add support of mips by manually configure opkg.conf.

#vi /etc/opkg.conf 

Add the below lines at the end of the file:

#originally supported architecture
arch all 1

arch noarch 1
arch ralink 10
 
#Newly added lines
arch ramips_24kec 200
arch ramips 300
arch mips 400
arch unknown 500


Then save the file.  Check the print-architecture again:

#opkg print-architecture
arch all 1
arch noarch 1
arch ralink 10
arch ramips_24kec 200
arch ramips 300
arch mips 400
arch unknown 500

Now it support MIPS!

Now I can install the ipk again:

#opkg install xxxx_ramips_24kec.ipk
Installing xxxxxx to root...
Configuring xxxxx.
xxxx Server has started.


It can be installed and run successfully!