ACC-72EX User Manual
DPRAM Data Processing
59
Command and Acknowledge
To ensure data consistency over the content of a mailbox, the firmware uses a pair of flags, each for one
direction. Engaging these flags gives access rights alternating to either the user application or the netX
firmware. If both UMAC and netX firmware were to access the mailbox at the same time, it may cause
loss of data or inconsistency.
As a general rule, if both flags have the same value (both are set or both are cleared), the process which
intends to write has access rights. If they have a different value, the process which intends to read has
access rights. The following table illustrates this mechanism.
Send Mailbox
CMD Flag
ACK Flag
UMAC Has Write Access
0
0
netX Has NO Read Access
UMAC Has NO Write Access
0
1
netX Has Read Access
UMAC Has NO Write Access
1
0
netX Has Read Access
UMAC Has Write Access
1
1
netX Has NO Read Access
Receive Mailbox
CMD Flag
ACK Flag
UMAC Has NO Read Access
0
0
netX Has Write Access
UMAC Has Read Access
0
1
netX Has NO Write Access
UMAC Has Read Access
1
0
netX Has NO Write Access
UMAC Has NO Read Access
1
1
netX Has Write Access
