ESP8266 SPI flash runs at 40Mhz

[ralphd]

I had some fun with my Rigol scope measuring the SPI clock on an ESP8266 module.  I didn't know if it would run at the same speed as the CPU clock, or half speed.  Given that it runs at half speed and the flash is rated for 80Mhz, it would seem pretty safe to clock the ESP8266 at 160Mhz instead of the default 80.  I've attached one scope shot.  For more details, see my blog post.
http://nerdralph.blogspot.ca/2015/03/esp8266-spi-flash-performance.html