#ESP8266 USB Software Driver

WARNING: THIS PROJECT IS A WORK IN PROGRESS. DO NOT EXPECT IT TO WORK WELL.

Forum for discussion of development: http://www.esp8266.com/espusb

I wanted to have USB on the ESP8266, and a while ago I saw on the ESP32 flier, it read: "Rich Peripherals" ... "Sorry, no USB!" I thought to myself, that is ridiculous. Of course there's USB.

So, it was born. This is a software USB stack running on the ESP8266/ESP8285. It requires only one external resistor, between D- and 3.3V.

Currently, the chip expects D- on GPIO 4 and D+ on GPIO 5 - but any GPIO pair may be used. It is important to note that both D- and D+ MUST be adjacent.

Additionally, this only operates with low-speed USB (1.5 MBit/s), ideal for making peripherals, not for fake networkand devices usb-serial bridges. That said - you can still write "control" messages that communicate with the ESP8266. Control messages are a great way to encapsulate your data since they handle all the framing and describing what function you wish to pass data for.

More info hopefully coming soon.

Hardware

NOTE: GPIO12/14 do not need to be connected to ground. GPIO15 may be connected via a pull-down resistor. For stability, a pull-up on GPIO2 is recommended.

Also, checkout the hardware/ folder. It has kicad designs for my tiny board. Though they are for the ESP8285, the same pin configuration may be used to run on the ESP8266.

Memory Usage

This is typical memory usage for a two-endpoint (in addition to EP0) device.

In summary:

Total SRAM: 232 bytes + Descriptors (~317 bytes)

Total Flash/IRAM (Only iram, tables and usb_init can be stuck in slow flash): 1422 bytes

More details:

SRAM:

0000007c D usb_ramtable
0000006c B usb_internal_state

IRAM:

You must write: usb_handle_custom_control - the demos here hook it up to the command engine which allows self flashing on 1MB+ parts.

C functions:

0000002a T usb_pid_handle_ack
0000014f T usb_pid_handle_data
00000022 T usb_pid_handle_out
000000e9 T usb_pid_handle_in
00000002 T usb_pid_handle_sof
00000039 T usb_pid_handle_setup

From/To (in ASM):

40100f20 t usb_asm_start
401011ef t usb_asm_end
Total length of ASM: 2cf