So with a CH340 I was able to set flashing baud to 921600 and it flashes effectively at 850kbps.
And with a CP2102N I was able to get the communication rate up to 2000000 (2M) but the effective flashing rate does not improve.Wrote 1388912 bytes (858612 compressed) at 0x00020000 in 13.8 seconds (effective 806.8 kbit/s)...
At 3000000baud (3M) flashing fails around 66-75% completion.Wrote 1388912 bytes (858612 compressed) at 0x00020000 in 13.5 seconds (effective 825.8 kbit/s)...
I tried turning off compression, but that doesn't help.
The fact that 2M baud seems to communicate well, yet flashing only runs at 825.8 kbit/s leads me to believe that there's a bottleneck at the flash writing, but I can't seem to find any documentation of a maximum flashing speed.
Is there anything I can do to speed up the flashing process? or have I hit the limit?