I use VI to edit the .asm file

then I call a shell script that calls:
asx8051 which assembles into an object file
sdcc to link and produce a .ihx file

then I call a program that I wrote that sends the ihx file over the serial port, to my 80c552 board, in the format that its ROM loader is expecting (quantity, code bytes, checksum, etc., then follow up with a jump address)

The ROM loader will automatically load the program in memoy, at the adress specified, and the transfer execution to it. After my program is done, I make sure an "ljmp $0" is called, to resume execution with the ROM loader. This avoids having to power off then on :)

It's an intellectually rewarding experience...