DS3134 datasheet(136/203 Pages) DALLAS

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DS3134

136 of 203

010 = middle buffer transmission complete of a multi-buffer packet (DQS = 1)

011 = last buffer transmission complete of a multi-buffer packet (DQS = 1)

100 = software provisioning error; this channel was not enabled

101 = descriptor error; either byte count = 0 or channel code inconsistent with Pending Queue

110 = PCI error

111 = transmit FIFO error; it has underflowed

dword 0; Bits 29 to 31 / Unused. Not used by the DMA. Could be any value when read.

The Host will read from the Transmit Done Queue to find which data buffers and their associated

descriptors have completed transmission. The Transmit Done Queue is circular queue. To keep track of

the addresses of the circular queue in the Transmit Done Queue, there are a set of internal addresses

within the device that accessed by both the Host and the DMA. On initialization, the Host will configure

all of the registers shown in Table 8.2.4A. After initialization, the DMA will only write to (i.e. change)

the write pointer and the Host will only write to the read pointer.

Empty Case

The Transmit Done Queue is considered empty when the read and write pointers are identical.

Transmit Done Queue Empty State

empty descriptor

read pointer >

empty descriptor

< write pointer

empty descriptor

Full Case

The Transmit Done Queue is considered full when the read pointer is ahead of the write pointer by one

descriptor. Hence, one descriptor must always remain empty.

Transmit Done Queue Full State

valid descriptor

empty descriptor

< write pointer

read pointer >

valid descriptor

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