22

RSAR = ((BNRY + 1) << 8) + PktPointer.

RBCR = PktLen - PktPointer.

Use remote DMA to read packet data into offset PktBuffer + PktPointer.

PktPointer = 0.

If PktPointer = 0,

Do the normal driver packet received procedure,

but get packet data from PktBuffer, not the receive buffer ring.

Else go to interrupt entry to poll ISR again.

Rx condition

ISR

RSR

CURR

CLDC

Packet

header

or

page data received

1

0

BNRY+1

<>0

Total packet received

1

1

BNRY+1 +

(packet pages)

= 0

More then one packet

1

0

BNRY+1 +

(packet pages)

<>0

CRC or page align

error

44

X

X

13.

In order to provide the VT86C926 with parallel processing between the ISA bus and Ethernet media, the

VT86C926 must be set to detect early transmit error mode. This error may occur when the system's master

device uses the ISA bus and then uses the data bus.

If the ETEN bit is set in the configuration register B, the transmit status status bit5 (ETUN) and the transmit

error status bit (TXE) in the interrupt service register (ISR) bit 3 would be set on. If the interrupt mask

register TXEE bit is set to on, an interrupt will be generated when the local DMA pass the remote DMA

machine.

This mode is essentially similar to the Early Interrupt Receive Mode. When the VT86C926 is under the

normal mode, the CPU can issue the "transmit packet" command to the VT86C926 and the internal local

DMA will tranfer the data from the SRAM to the Ethernet. However, the packet data must already exist in

SRAM.

In the situation in which the "transmit packet" command is issued to the local DMA and the remote DMA

(to fill SRAM) at the same time, a corrupt packet may be transmitted to the network and remain undetected.