First - Sorry about the rather vague title, I didn't know how to word this issue.
I've been working on the new tinyAVR (404 and 817) devices. I've been playing around with a UART bootloader, using Microchip's own design (AN2634 - https://www.microchip.com/wwwApp...). It's a pretty simple bootloader which I could get running without much hassle. The bootloader always receives and then echoes the full flash size number of bytes (8192 for the 817, 4096 for the 404). I'm using an 817 Xplained Mini board for experimenting with and my actual project is on a tinyavr 404 on my custom PCB.
My issue: When I use the Xplained mini board with the mEDBG as the virtual com port at baud 115200, the 8192 byte transfer takes only 4-5 seconds. For my own board which does not have a USB-UART inbuilt, I'm using an Arduino Mega's USB-UART RX and TX pins (having connected the mega's reset pin to ground) since i lost my CH340 converter and am waiting for more to arrive. The mega has an atmega16u2 handling the usb-uart stuff. With this setup, the 4096 byte transfer to the tinyavr 404 at 115200 baud takes 17 seconds. I'm running both the 817 and the 404 at the same clock speed (20E6/6).
I was under the impression that the same baud rate of 115200 should mean the same speed, so the 404 with half the size of flash would have taken hardly 2-3 seconds to complete. If anyone has an idea of why this could be happening, i'd love to know.