Patience is my second name, but I hope you will try to read the instructions provided before rushing to upgrading the switch, because every letter matters there and it is very easy to mess up things.
I think we need to go back to the release notes located here https://support.hpe.com/hpesc/public/docDisplay?docId=a00061838en_us and check again the section 'TFTP download through an Ethernet port'.
The section depicts a scenario when your laptop is connected over the console cable and you have separate TFTP server connected over the Ethernet cable to the switch. However, I can offer you a slight modification that will look a little bit differently from the physical point of view, but will be absolutely the same logical setup.
Let's follow my guide now.
1. Get a laptop with Ethernet port
2. Get a Ethernet cable
3. Get a console cable for the switch
4. Download TFTPD32 or TFTPD64 software (I assume you run Windows on your laptop) from here - http://tftpd32.jounin.net/tftpd32_download.html
5. Download 5120.EI-4210G-4510G_5.20.R2222P11 software from here https://h10145.www1.hpe.com/downloads/SoftwareReleases.aspx?ProductNumber=JE067A and unpack it to a temporary directory. You will need two files:
- A5120EI-BTM-621.btm
- A5120EI-CMW520-R2222P11.bin
6. Connect the console cable to your laptop and to the console port of the switch, open up Putty and ensure you have a connection (see the output and can type)
7. Connect the Ethernet cable from step 2 one end to the first port of your switch and another port to the Ethernet port of your laptop.
8. Set the IP address on the Ethernet NIC of your laptop to 10.0.0.1 mask 255.255.255.0
9. Start TFTPD32 software, go to Settings, ensure TFTP Server is enabled and the Base directory points to the directory where you unpacked .BIN and .BTM files on Step 5. Press OK and in the Server Interface field select the NIC with IP 10.0.0.1
10. Reboot the switch, enter the Extended Bootrom
11. Follow the instructions from the release notes I have mentioned in the beginning of this message, in particular Step 3 of the 'Upgrading Boot ROM' section. Use following information during the TFTP download:
Load File Name: A5120EI-BTM-621.btm
Switch IP address: 10.0.0.2
Server IP address: 10.0.0.1
12. After successful download and Bootrom update followed by the switch reboot, proceed with 'Upgrading system software' section. Use same IP addresses as in Step 11, but this time use 'A5120EI-CMW520-R2222P11.bin' as the filename to download and set it to 'Main' after the download completes. All as per instructions in the release notes.
13. Reboot the switch and this time it should boot up normally
Hope this helps!
P.S. If TFTP connection doesn't work, check IP addressing first and, second either allow incoming TFTP connections in Windows Firewall or disable the Firewall completely for the time of the upgrade.