2.2 BSP Rel. 1.0 for PPMC-275 Programmer's Guide

List of APIs API Call Reference
the descriptor passed to the sdmaChanReceive caller containing
received information from the MPSC channel. In Tx process, this
will be the descriptor that will be assigned with the user packet
info and transmitted.
'used' This index points to the descriptor that need to restore its
resources. For example in Rx process, using sdmaRxReturnBuff
will attach the buffer returned in packet info to the descriptor
pointed by 'used'. In Tx process, using sdmaTxReturnDesc will
merely return the user packet info with the command status of the
transmitted buffer pointed by the 'used' index. Nevertheless, it is
essential to use this routine to update the 'used' index.
'first' This index supports Tx Scatter-Gather. It points to the first descriptor
of a packet assembled of multiple buffers. For example when in
middle of such packet we have a Tx resource error the 'curr' index
get the value of 'first' to indicate that the ring returned to its state
before trying to transmit this packet.
Receive operation The sdmaChanReceive API return the caller the packet information
struct pointer describing the current SDMA descriptor containing
the received information. It is the user responsibility to
return this resource back to the Rx descriptor ring to enable the
reuse of this source. Return Rx resource is done using the
sdmaRxReturnBuff API.
Transmit operation The sdmaChanSend API supports Scatter-Gather which enables to
send a packet spanned over multiple buffers. This means that for
each packet info structure given by the user and put into the Tx
descriptors ring, will be transmitted only if the 'LAST' bit will be
set in the packet info command status field. This API also considers
the protocol used and its restriction regarding buffer alignments
and sizes. The user must return a Tx resource after ensuring
the buffer has been transmitted to enable the Tx ring indexes to
update.
Software Modules
This driver is implemented in:
• sdma.c
• sdma.h
5 - 46 VxWorks 5.5/Tornado 2.2 BSP Rel. 1.0 for PPMC-275