Bringing Up the System (Debugging)
Communication unit
Copyright © 2002 Marvell
CONFIDENTIAL
Doc. No. MV-S300165-00, Rev. A
May 21, 2002, Preliminary
Document Classification: Proprietary Information
Page 145
Section 21. Bringing Up the System (Debugging)
21.1 Communication unit
21.1.1 MPSC Packets Transmission Stops
The Shadow Byte Count filled (see
) can be used to debug this problem. Each time a
transmit descriptor is fetched, the Shadow Byte Count is loaded with the Byte Count field value. Each transmit
burst decrements the Shadow Byte Count field value.
When the Shadow Byte Count field reaches zero, the descriptor is closed and the pointer moves to the next
descriptor. For normal operation, the Shadow Byte Count field value must be initialized to the same value as the
Byte Count field value.
For debugging purposes, the Shadow Byte Count field can be initialized to an unreasonable value (e.g 0xFFFF). If
the Shadow Byte Count field remains with this value, it means that the descriptor has not been fetched. In addi-
tion, the Tx descriptor pointer and the transmit demand value must be checked to confirm that the packet was sup-
posed to be transmitted.
The conclusion of such debugging is that the MPSC machine initilization is wrong.