XMOS is the designer and manufacturer of a family of microcontrollers offering a fast 32b CPU with an interesting concurrency model based on hardware-supported threading.
Their lowest cost devboard is the XCARD XK-1A, which, at $60 offers you two XS-L1 uCs, one in TQ128 on a breakout, and the other in TQ64 complete with a high-speed USB transceiver and 13MHz crystal.
XMOS intends for the USB-enabled device to be used as a debug & commmunication gateway for the second chip, but the runtime loading of application code means that it can, theoretically, be used as a general purpose devboard for the creation of USB-enabled XMOS devices.
XMOS provides decent documentation for the bootloader, but doesn't offer a general-purpose tool for loading user-specific firmware onto the device.
This project is that missing piece.
Order the XTAG2 on DigiKey for $19! Part number "XCARD XTAG-2-ND"
- ULPI USB Reset is on "XS1_PORT_1I"
- All IO pins are 3v3
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Pin 1bit 4bit 20pin Signal
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VUSB 1
X0D35 P1L0 3 TARGET_TRST_N
X0D0 P1A0 5 TARGET_TDO
X0D10 P1C0 7 TARGET_TMS
X0D11 P1D0 9 TARGET_TCK
X0D34 P1K0 11 TARGET_DBG
X0D1 P1B0 13 TARGET_TDI
X0D36 P1M0 15 TARGET_RST_N
X0D25 P1J0 17 TARGET_UART_TO_TARGET
X0D26 P4E0 19 TARGET_UART_FROM_TARGET
NC 2
GND 4
X0D7 P4B3 6 TARGET_XLINK_FROM_TARGET_1
GND 8
X0D6 P4B2 10 TARGET_XLINK_FROM_TARGET_0
GND 12
X0D5 P4B1 14 TARGET_XLINK_TO_TARGET_0
GND 16
X0D4 P4B0 18 TARGET_XLINK_TO_TARGET_1
GND 20
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CAVEAT: all pins on all four-bit ports cannot be used in applications using XUD, XMOS's USB stack. See the XS-1 Design Guide for details.