I have slowly been integrating and bringing up the USB low-speed example (i.e. the ST USBLS Library 4.21) from C:/RIDE/EXAMPLES/ST7/REVA/63B/COSMIC/ST7USBLS/ and, because debugging over ICC doesn't seem to work, have been trying to get serial working over SCI.

However, when I enable interrupt mode SCI usage with:

SCI_Init(SCI_DEFAULT_PARAM1, SCI_DEFAULT_PARAM2);
SCI_Select_Baudrate(SCI_PR_13 | (SCI_TR_4 | SCI_RR_4)); // 9600 @ Fcpu = 8 MHz
SCI_Mode(SCI_TX_ENABLE);
SCI_IT_Enable(SCI_TRANSMIT_REGISTER_READY |
SCI_FRAME_TRANSMITTED);

the USB enumeration fails, regardless of whether I actually use the SCI via printf or SCI_PutString. If I simply #if 0...#endif the above SCI initialization code, the USB enumeration works again.

Is there anything expressly restricted or forbidden about using these two blocks concurrently? Neither pins are multiplexed, so I cannot see that there would be.