Похоже Вам не повезло с поддержкой симулятором Keil выбранного Вами ARM. Уж больно куцый список VTREG. Сравните:
dir vtreg
TRAPS: ulong, value = 0x0000005F
DBGCOMCR: ulong, value = 0x00000000
DBGCOMRD: ulong, value = 0x00000000
DBGCOMWR: ulong, value = 0x00000000
XTAL: ulong, value = 0x00B71B00
IRC: ulong, value = 0x003D0900
RTCX: ulong, value = 0x00008000
PLLIN: ulong, value = 0x00B71B00
HCLK: ulong, value = 0x112A8800
CCLK: ulong, value = 0x02DC6C00
USBCLK: ulong, value = 0x02DC6C00
V3: float, value = 3.29999995
PORT0: ulong, value = 0xFFFFFFFF
PORT1: ulong, value = 0xFFFFFFFF
PORT2: ulong, value = 0x00003FFF
PORT3: ulong, value = 0x078000FF
PORT4: ulong, value = 0xF300FFFF
S0IN: ushort, value = 0xFFFF
S0OUT: ushort, value = 0x0000
S0TIME: uchar, value = 0x01
S0BAUD: ulong, value = 0x00002580
S1IN: ushort, value = 0xFFFF
S1OUT: ushort, value = 0x0000
S1TIME: uchar, value = 0x01
S1BAUD: ulong, value = 0x00002580
S2IN: ushort, value = 0xFFFF
S2OUT: ushort, value = 0x0000
S2TIME: uchar, value = 0x01
S2BAUD: ulong, value = 0x00002580
S3IN: ushort, value = 0xFFFF
S3OUT: ushort, value = 0x0000
S3TIME: uchar, value = 0x01
S3BAUD: ulong, value = 0x00002580
I2C0_IN: ushort, value = 0xFFFF
I2C0_OUT: ushort, value = 0xFFFF
I2C1_IN: ushort, value = 0xFFFF
I2C1_OUT: ushort, value = 0xFFFF
I2C2_IN: ushort, value = 0xFFFF
I2C2_OUT: ushort, value = 0xFFFF
SPI_IN: ushort, value = 0x0000
SPI_OUT: ushort, value = 0x0000
SSP0_IN: ushort, value = 0x0000
SSP0_OUT: ushort, value = 0x0000
SSP1_IN: ushort, value = 0x0000
SSP1_OUT: ushort, value = 0x0000
VREF: float, value = 3.29999995
AD00: float, value = 0
AD01: float, value = 0
AD02: float, value = 0
AD03: float, value = 0
AD04: float, value = 0
AD05: float, value = 0
AD06: float, value = 0
AD07: float, value = 0
AOUT: float, value = 0
CAN1ID: ulong, value = 0x00000000
CAN1L: uchar, value = 0x00
CAN1B0: uchar, value = 0x00
CAN1B1: uchar, value = 0x00
CAN1B2: uchar, value = 0x00
CAN1B3: uchar, value = 0x00
CAN1B4: uchar, value = 0x00
CAN1B5: uchar, value = 0x00
CAN1B6: uchar, value = 0x00
CAN1B7: uchar, value = 0x00
CAN1IN: ushort, value = 0x0000
CAN1OUT: ushort, value = 0x0000
CAN2ID: ulong, value = 0x00000000
CAN2L: uchar, value = 0x00
CAN2B0: uchar, value = 0x00
CAN2B1: uchar, value = 0x00
CAN2B2: uchar, value = 0x00
CAN2B3: uchar, value = 0x00
CAN2B4: uchar, value = 0x00
CAN2B5: uchar, value = 0x00
CAN2B6: uchar, value = 0x00
CAN2B7: uchar, value = 0x00
CAN2IN: ushort, value = 0x0000
CAN2OUT: ushort, value = 0x0000
DCC_SIN: ushort, value = 0xFFFF
DCC_SOUT: ushort, value = 0x0000
DCC_TIME: uchar, value = 0x01