A smaller than tiny USB Host library for the Raspberry Pi Pico/W (rp2040/rp2350).
The rp2040/rp2350 chips in the Raspberry Pi Pico/W boards support USB Host and USB Device modes. Most examples and implementations use the excellent TinyUSB library to provide this support. However, TinyUSB has some limitations. These include a somewhat hard coded initial configuration that requires the code to be recompiled when changes are made.
The goal of this repo is to offer a simple USB Host library, using only the code from https://github.com/raspberrypi/pico-sdk. Ideally, this could help form the basis, or at least inspire, other efforts. Since the initial target is for the Pico/W boards and since the goal is to be tiny, even "tinier" than TinyUSB, it seems the name PicoUSB is fitting.
The current status, as of the end of November 2024, showing the output from enumeration of an FTDI board.
Since we are taking over the physical USB connector on the board, the easiest way to program the board and test things out is by using a pico debug unit. These can be purchased from numerous sources. The .vscode directory contains some configuration for this setup.
Since this repo doesn't use TinyUSB at all, we need to disable it from the
pico-sdk code. The only way I found to do this is by commenting out the
following lines in ${PICO_SDK_PATH}/src/rp2_common/CMakeLists.txt.
# pico_add_subdirectory(tinyusb)
# pico_add_subdirectory(pico_stdio_usb)
NOTE: A hardware polled endpoint needs FOUR things to fire:
1) usb_hw->int_ep_ctrl |= (1 << epn) ; // Activate the endpoint
2) *ep->ecr |= EP_CTRL_ENABLE_BITS ; // Enable EP in ecr
3) *bcr = hold | USB_BUF_CTRL_AVAIL ; // Buffer is available
4) usb_hw->sie_ctrl = sie | USB_SIE_CTRL_START_TRANS_BITS; // Start transfer
BSD-3-Clause license, the same as code in pico-examples.