esp8266 firmware upgrade, odd baudrate in bootloader?

So, I also got one of those ESP8266 wifi/serial modules, which are pretty neat. Unfortunately mine seemed to come with an ancient firmware on it, and pretty unconveniently those didn't want to be re-flashed with newer software.

From Chris’ Miscellanea

The bootloader seems to initialize the modules' serial port to the pretty insane value of 76923 bps, so that in "programming" mode, the stupid windows-utility (or, for that matter, any program expecting standard-baudrates) will fail to communicate with the module.

From Chris’ Miscellanea

If you have a suitable serial cable (a FTDIchip FT2232 is what I used), you can calculate "custom dividers" for most uncommon baudrates, and use those instead of 38,4kBps (the "magic" baudrate indicating that the custom one should be used).

Base-frequency for the ft2232 is 60 Mhz, so we'll use a custom divisor of 780 (60Mhz/76923).

$ setserial /dev/ttyUSB0 spd_cust divisor 780     
$ cu -l ttyUSB0 -s 38400
Connected.

 ets Jan  8 2013,rst cause:1, boot mode:(7,7)

waiting for host

 ets Jan  8 2013,rst cause:1, boot mode:(7,7)

waiting for host

 ets Jan  8 2013,rst cause:1, boot mode:(3,7)

load 0x40100000, len 24444, room 16 
tail 12
chksum 0xe0
ho 0 tail 12 room 4
load 0x3ffe8000, len 3168, room 12 
tail 4
chksum 0x93
load 0x3ffe8c60, len 4956, room 4 
tail 8
chksum 0xbd
csum 0xbd

Interestingly, that seems to be only the bootloader of the module, after this, the device switches to the more common 115200kbps and responds to AT-commands, given that GPIO15=GND, GPIO2=Vcc, GPIO0=Vcc and CH_PD=Vcc. (pullups to Vcc via ~5kΩ resistor)

So, to get the windows-only updater to run successfully, we...

• connect GPIOs and CH_PD as listed above (AT-Mode)
• power up module
• module will start bootloader with 77kbps, then change into AT-command mode, at 115200 bps
• connect GPIO0 to GND (firmware download mode)
• pulse CH_PD to LOW to restart module
• firmware will restart, but bootloader does NOT go back to 77kbps
• run firmware-upgrade in windows

From Chris’ Miscellanea

Now I'm upgraded to version 170901 (whatever that means).

AT+GMR
00170901