[RPRWG] Credit A0 maybe zero or negative?

["Jiang zhou" <zjiang@xxxxxxxxxxxxxxxxxxx>]

For the MAC control frame sending it needs subtract both shM and shA0. If
control frame set PT as A0,it maybe result credit to zero or negative.

In the transmit seletction table:

!EntryInMacControl() ||passM == 0         2     CHECK
sizeOfMacControl > spaceInPTQ             3     CHECK
¡ª                                        4     TxMacControl()

If now the passM !=0 and passA0 =0(creditA0 < sizeMTU) and there is long
control frame(near sizeMTU) in control queue. More no frame in PTQ or STQ.

So according 4 this frame is sent out. When it sends MAC need subtract the
creditA0.
If the control frame length > creditA0 , crditA0 may be negative.


Best Regards
Jiangzhou
zjiang@xxxxxxxxxxxxxxxxxxx