The Blackhawk USB560v2 STM emulator has System Trace capability, along with a USB powered interface.

JTAG Emulator
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Product, Description, Price (US dollars)
Blackhawk USB560v2 (p/n 12202), XDS560v2 class emulator with trace capability – USB2.0 interface. Only required for C/C++/Assembler development, 1000
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