I made a few small mods to the Mega8 serial bootloader from the Academ (author Carlott). It's in assembly language and fits in 512 bytes. Installed it using an AVR ISP serial port dongle.
Now, towards the goal using the serial boot loader, after fumbling in the dark, by trial and error, I discovered that Atmel's AVRProg.exe works with this code. AVRStudio includes AVRProg.exe. The Mega8 bootloader has to be activated by sending an ESC character right after power up, then close that serial link, and then run AVRProg from a DOS prompt.
I do not have an STK500.
AVRProg.exe apparently has no built in help (like a -? switch). I discovered that STK500.exe has a -h and -? switch which produces some useage info which is also in the AVRStudio documentation. Some (all?) of the command line switches for STK500.exe also work with AVRProg.exe.
Is there a doc for AVRProg.exe?
Secondly - it appears that AVRProg.exe sets the chosen serial port to 19.2Kbaud - I see no switch to change the rate.
Maybe there's a better 512 byte bootloader, with a PC side program (preferrably GUI based). I found a few larger bootloaders on AVRFreaks, but this Mega8 loader was the first I tried. My goal is to use this bootloader on a 900MHz wireless serial link (MaxStream) at 56K or 110K baud.
I have the 19.2K Mega8 bootloader working with AVRProg, but don't know if the latter can be told to go faster.
Thanks in advance for your help.