RELEASED
PM7380 FREEDM-32P672
DATA SHEET
PMC-1990262
ISSUE 5
FRAME ENGINE AND DATA LINK MANAGER 32P672
TRANS:
The indirect transmission start bit (TRANS), in concert with the LEVEL[3:0]
bits, configure the various channel FIFO free space levels which trigger the
HDLC processor to start transmission of a HDLC packet as well as trigger the
partial packet buffer to make DMA request for data as shown in the following
table. The transmission start mode to be written to the channel provision
RAM, in an indirect write operation, must be set up in this register before
triggering the write. TRANS reflects the value written until the completion of a
subsequent indirect channel read operation.
The HDLC processor starts transmitting a packet when the channel FIFO free
space is less than or equal to the level specified in the appropriate Start
Transmission Level column of the following table or when an end of a packet
is stored in the channel FIFO. When the channel FIFO free space is greater
than or equal to the level specified in the Starving Trigger Level column of the
following table and the HDLC processor is transmitting a packet and an end
of a packet is not stored in the channel FIFO, the partial packet buffer makes
expedite requests to the TMAC672 to retrieve XFER[3:0] + 1 blocks of data.
To prevent lockup, the channel transfer size (XFER[3:0]) can be configured to
be less than or equal to the start transmission level set by LEVEL[3:0] and
TRANS. Alternatively, the channel transfer size can be set, such that, the
total number of blocks in the logical channel FIFO minus the start
transmission level is an integer multiple of the channel transfer size. The
starving trigger level must always be set to a number of blocks greater than or
equal to the channel transfer size.
Table 26 – Level[3:0]/TRANS Settings
LEVEL[3:0]
Starving
Start
Start Transmission
Level (TRANS=1)
Trigger Level
Transmission
Level (TRANS=0)
0000
0001
0010
0011
0100
2 Blocks
1 Block
1 Block
(32 bytes free)
(16 bytes free)
(16 bytes free)
3 Blocks
2 Blocks
1 Block
(48 bytes free)
(32 bytes free)
(16 bytes free)
4 Blocks
3 Blocks
2 Blocks
(64 bytes free)
(48 bytes free)
(32 bytes free)
6 Blocks
4 Blocks
3 Blocks
(96 bytes free)
(64 bytes free)
(48 bytes free)
8 Blocks
6 Blocks
4 Blocks
(128 bytes free)
(96 bytes free)
(64 bytes free)
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA,INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
221
PMC [ PMC-SIERRA, INC ]
