Chaos Communication Congress

No USB? No problem. (33x65)

Data di messa in onda: Dic 28, 2016

Speaker: Xobs How to get USB running on an ARM microcontroller that has no built in USB hardware. We'll cover electrical requirements, pin assignments, and microcontroller considerations, then move all the way up the stack to creating a bidirectional USB HID communications layer entirely in software. USB is amazing. It's hot-pluggable, auto-negotiating, and reasonably fast. It's robust, capable of supplying power, and works cross-platform. It lives up to the “Universal” claim: your PC definitely has USB, but it may not have TTL Serial, I2C, or SPI available. Hardware USB support is available in all manner of embedded microcontrollers. However it's not available on all microcontrollers, and integrating a hardware USB PHY can double the cost of a low-end microcontroller. This problem is particularly acute in the sub-$1 microcontrollers: a companion USB PHY chip would typically cost more than the microcontroller (example: the MAX3420E USB-to-SPI adapter costs around $5), so your only option for USB is to get your hands dirty and bit bang the missing protocol. This talk describes the implementation of a new bitbanged USB stack, starting with a primer on the USB PHY layer and continuing up the stack, concluding with "Palawan", a feature-complete open-source bitbanged USB Low Speed stack available for use on microcontrollers priced for under a dollar. We'll go over requirements for getting USB to work, as well as talking about USB timing, packet order, and how to integrate everything together. Unlike other bitbang USB implementations such as V-USB and LemcUSB, Palawan makes fewer assumptions about GPIO layout. With Palawan, USB's D+ and D- signals can be on different GPIO banks, and need not be consecutive. By doing so, more pins are available to the user, making it easier to use with devices that have special restrictions on what pins can do what. The only requirements are that both GPIO pins can be both inputs and push-pull outputs, and that at least one pin c