ethernet/toshiba/spider_net.rst

44 descriptor pointer (GDACTDPA). The GDACTDPA points at the descr
45 currently being filled. When this descr is filled, the hardware
47 flowing RX traffic, every descr behind it should be marked "full",
49 discovers that the current descr is not empty, it will signal an
54 descr. The OS will process this descr, and then mark it "not-in-use",
64 a "not-in-use" descr. The OS will perform various housekeeping duties
65 on this descr. This includes allocating a new data buffer and
67 then mark the descr as "empty", ready to receive data. Thus, when there
71 pointer, at which point the OS will notice that the head descr is
75 all be pointing at the same descr, which should be "empty". All of the
86     net eth1: Chain tail located at descr=20
93 In the above, the hardware has filled in one descr, number 20. Both
97 The "Have nnn decrs" refers to the descr starting at the tail: in this
98 case, nnn=1 descr, starting at descr 20. The "Last nnn descrs" refers
132 it will restart at the next descr. This potentially will lead to a
133 deadlock condition, as the tail pointer will be pointing at this descr,
135 this descr to be filled. However, the hardware has skipped this descr,
137 is a potential deadlock, with the OS waiting for one descr to fill,
146     net eth1: Chain tail located at descr=255
156 Both the tail and head pointers are pointing at descr 255, which is
159 that everything in front of the "empty" descr must surely also be empty,
160 as explained in the last section. The OS is waiting for descr 255 to
163 The HW pointer is at descr 0. This descr is marked 0x4.. or "full".
166 "full", while descr 254 and 255 are empty. (The "Last 1 descrs" is
167 descr 254, since tail was at 255.) Thus, the system is deadlocked,
174 the hardware has skipped a descr or two (sometimes dozens under heavy
176 search the ring for the next full descr, and the driver will resume
196 marks a descr about 1/4th of the way from the bottom of the queue, so
197 that an interrupt is generated when the descr is processed. This