How to fix SIM800L cyclic reboot after unsuccessful flashing?

Question

Arduino

Greetings. Faced a problem after flashing SIM800l. I connect via arduino uno. I don't have a UART converter. rx > rx, tx respectively. Powered directly from a 3.7V battery connected to the charging module.
To the point: I decided to reflash. After reading the lessons, determining what firmware I need, I got down to business.
The firmware was already coming to an end, but suddenly it gave an error:
S_FT_DOWNLOAD_CHKSUM_MISMATCH ( 4009)

Googling, I realized that I could not find the answer, I decided to try to flash it again, but the module stopped showing signs of life. The light bulb does not blink, incomprehensible characters are sent to Serial at an incomprehensible frequency. But, after reboot sends legible text:

F1: 5004 0000
00: 102C 0001
01: 1005 0000
U0: 0000 0001 [0000]
T0: 0000 00A3
Boot failed, reset ...

Something like this, maybe someone has come across this, I will be glad to advice. Before that, everything was fine, sms / zhprs / calls worked.