After ages of waiting for components to arrive from China (and some didn’t, so I had to reorder).
I was finally ready to assemble the M4 board. After applying the solder mask and doing pick and place, I found the GL2000 bi-directional level converter was the wrong package :/ – Oh well added the other components as there is enough work to do without it for now. Also a couple of other screwups, ie. swapped miso and mosi on the flash, used wrong SCK pin on ESP-12E (notice it is PIN 12 that’s spi-clock). So eventually I will have to re-do the PCB.
Update: It’s not entirely true, it is because there is two (known) different ESP-12E modules in existence, see here http://www.esp8266.com/viewtopic.php?f=5&t=3163 My initial layout wasn’t wrong, I just got a 12E module with a different pin layout :/
For now, the MCU, SD and SPI flash is working, I can access the ESP8266 wifi chip and read/write the spi flash from the Cortex M4 (keep the ESP in reset state and do spi access) and obviously send serial commands.
However the plan is to make an IPC interface via SPI between the Cortex M4 and the ESP-8266 to get proper performance.
I will update on this as I get along.