NEC VR4133 - Manual (Page 6)

Operating Precautions for V R 4133 TM
No. 5
Write access to external I/O area
(Direction of usage)
Details
A write cycle to external I/O or Flash area after
• a CPU read/write access to a BCU-managed registers Note
• or a CPU I/O read after a bus hold
• or a DMA I/O read after a bus hold
• or a Flash memory read
may drive the wrong write data. To avoid this situation, one of the following workarounds must be
implemented:
(1) execute a dummy register access to a non-BCU-managed register Note
(2) execute a dummy external I/O write or Flash write before the actually intended external
write
Note: BCU-managed registers are all registers except
SCU registers
0x0f001000 – 0x0f001009
SDRAMU registers 0x0f000400 – 0x0f000409
PCIU registers 0x0f000c00 – 0x0f000d43
ETHER registers 0x0f001400 – 0x0f00193f
CEU registers 0x0f000e00 – 0x0f000e7f
No. 6
Branch delay slot of JAL(X) instruction in MIPS16 mode
(Specification change notice)
Details
A load of PC relative instruction must not be placed in the delay slot of a JAL(X) instruction in
MIPS16 mode. Therefore one of the following countermeasures must be taken:
(1) Do not locate a load of PC relative instruction in the delay slot of a JAL(X) instruction in
MIPS16 mode.
(2) Do not use JAL(X) instructions in MIPS16 mode; use JAL(X) in native mode instead.
As implementing these countermeasures requires changes in the compilers, MIPS16 will be
deleted from the V
R 4133 specification.
6 Customer Notification