What other ways can I signal the host?

eTPU_C

There are two other exception types: channel interrupts and data transfer interrupts. In those devices without DMA hardware, the two are indistinguishable. Assign values 0 or 1 to channel.CIRC, or use these macros from eTPUC_common.h.

// Channel control macros
#define SetChannelInterrupt()       (channel.CIRC = 0)
#define SetDataTransferInterrupt()  (channel.CIRC = 1)