For ESP8266
Populate R1, R2, R3, R4, R5 and R6. DON'T populate R7 or R14.

Populate R13 to use GPIO6 for CH_EN.

R8 is an optional 10K pullup for RST, as only using the internal pullup can lead to stability issues.

For Power, C1 0.1uf and C8 10uf should always be populated. If using the RPi's 3V3 supply put a wire / jumper across the two pin header at the bottom. If using a regulator populate the SOT223 (e.g. with AMS1117 or LD1117S33) and populate C6 10uf and C7 0.1uf.

For Audio
The audio uses GPIO12 and GPIO13 to which you need to remap PWM0/PWM1 (see below).
You probably want to use components with good tolerances here unless you don't care about audio quality. Although it might not matter as not much care was taken with the routing, its just an easy 'add on'.

Populate R9,R10 with 270R. C2,C3 with 33nf. R11, R12 with 150R. C4, C5 with 10uf. Then populate the PJ313D audio jack.
The two BAV99 SOT23 dual diodes are protection for the RPi's GPIO and are optional but very strongly recommended as its a few cheap diodes vs a potentially dead Pi.

Software

dtoverlay=sdio,poll_once=off

Reboot.

Building the Driver

Install prerequisite packages on Raspbian to build the kernel.

#make sure everything is up to date
sudo apt-get update && sudo apt-get -y upgrade
#install tools
sudo apt-get -y install bc rpi-update git libncurses5-dev

Get the kernel headers

cd ~
sudo wget https://raw.githubusercontent.com/notro/rpi-source/master/rpi-source -O /usr/bin/rpi-source && sudo chmod +x /usr/bin/rpi-source && /usr/bin/rpi-source -q --tag-update
rpi-source --skip-gcc

If this bug isn't fixed https://github.com/notro/rpi-source/issues/17 then modify ./linux/Makefile and remove the line that reads EXTRAVERSION = + (line 4). Then create a new file in the ./linux directory called .scmversion with just a + character in it.

Clone and install the ESP8089 driver.

cd ~
git clone https://github.com/al177/esp8089.git
cd esp8089
make
sudo make install

Then reboot. The module should come up and give you a wlan0 interface!

Rebooting

When you reboot the pi without removing power you may need to reset the esp8266. You can do this using the GPIO pin that you wired up to CH_EN (probably GPIO6)

echo 6 > /sys/class/gpio/export
echo low > /sys/class/gpio/gpio6/direction
echo high > /sys/class/gpio/gpio6/direction

If you need to reload the module without rebooting the pi, unload the driver first or it gets very upset.

sudo modprobe -r esp8089

Remapping Audio

Just add this to the bottom of /boot/config.txt

dtoverlay=pwm-2chan,pin=12,pin2=13,func=4,func2=4

You can force 3.5mm audio output (instead of hdmi) using raspi-config or by running

amixer cset numid=3 1

Test it

wget http://www.freespecialeffects.co.uk/soundfx/sirens/police_s.wav
sudo aplay police_s.wav

Debugging

Check

dmesg

For a line that reads:

mmc1: new high speed SDIO card at address 0001

You can also try the below to check the ESP8266 is identifying as you'd expect.

sudo cat /sys/kernel/debug/mmc1/ios
clock:          50000000 Hz
actual clock:   41666666 Hz
vdd:            21 (3.3 ~ 3.4 V)
bus mode:       2 (push-pull)
chip select:    0 (don't care)
power mode:     2 (on)
bus width:      0 (1 bits)
timing spec:    2 (sd high-speed)
signal voltage: 0 (3.30 V)

pi@raspberrypi:~ $ cat /sys/bus/sdio/devices/mmc1\:0001\:1/modalias
sdio:c00v6666d1111

1 bit mode

You shouldn't need to use 1 bit mode, 4 bit mode should just work without removing the flash. So you can skip this step. I've left it here in-case you really want to use it this way.

If you want /HOLD asserted on the flash populate R7 (you may want to put a value there, e.g. 200R). Don't populate R3 or R4.
If using 1 bit mode you can re use GPIO27 as the enable pin for the
ESP8266 so populate R14. Otherwise populate R13 and use GPIO6.

If you're going to use the 1 bit mode you'll need the latest sdio device tree overlay. (this PR https://github.com/raspberrypi/linux/pull/1255).

sudo rpi-update
sudo reboot

Should bring it to you if you don't have it.

check if the sdio section has the bus_width parameter.

1 bit mode users must include the bus width parameter in their sdio overlay params.

dtoverlay=sdio,poll_once=off,bus_width=1

1 Bit-mode users also need to clear the QE bit in the SPI flash's register. Otherwise the flash will ignore the HOLD pin. I have a simple python script here to enable you to do that. Just download and run it. Ideally put the ESP8266 to sleep first (e.g. GPIO27 or GPIO6 low).

echo 6 > /sys/class/gpio/export
echo low > /sys/class/gpio/gpio6/direction

https://github.com/jacksonliam/rpi-bitbang-spiflash

wget https://raw.githubusercontent.com/jacksonliam/rpi-bitbang-spiflash/master/progflash.py
sudo python progflash.py