NEC manual Operating Precautions for VR4133 TM, Details

Operating Precautions for VR4133 TM

No. 7	Disconnect at the end of PCI burst cycle
	(Specification change notice)
	Details
	The last transfer of a PCI burst cycle is regarded as a disconnect cycle by VR4133, if STOP# and
	TRDY# are both asserted during the last-but-one data cycle, as shown in the following figure:
									unnecessary
	PCLK								cycle
	AD	A+0	D0	D1	A+8	D2	D3	A+12	D3
	FRAME#

IRDY#

TRDY#

STOP#

mis-understanding as disconnect

D0 ,D1,D2 are burst data; D3 is last burst data and D2 is last-but-one burst data. TRDY# and IRDY# are both asserted during D2 and D3. So data transfer of D2 and D3 is finished. But because of this restriction, VR4133 mis-interpreting data phase as if it is disconnected at D2. Therefore D3 cycle is performed again.

Therefore one of the following workarounds must be implemented:

(1)Do not use PCI-DMA function.

(2)Do not use LD and SD instructions and do not locate PCI memory and I/O areas in cached memory region of the CPU, so that burst cycles as shown above are not generated.

No. 8	Ethernet: receive short packet
	(Documentation errata)
	Details
	The packet size of VLAN is designed for minimum 68 bytes length, but this is not described in
	user’s manual.
	If a VLAN packet is received with a length of 64-67-byte (less than 68 byte), VR4133 will be
	judged it as a short packet, and a packet will be discarded.
	Using a packet with a length of less than 68 bytes can be realized by the following method:
	Set a ‘special value’ into VLTP (15:0) of VLTP0/1 (0x0f001464 / 0x0f001764) register. The
	‘special value' has not to be a VLAN type, which you want to receive. The data can be received
	as a usual packet, and judged as a VLAN packet by software. In this case, following items are
	different from usual VLAN procedure.

(1)All the VLAN packets recognized by the TYPE field of receiving descriptor status are described as normal packets.

(2)The statistics counter R64C0/1, R127C0/1, R255C0/1, R511C0/1, R1KC 0/1 and RMAXC0/1 count normal packets.

Customer Notification 7