Maxim Integrated 78Q8430 Software Driver - Manual (Page 11)

UG_8430_004 78Q8430 Software Driver Development Guidelines
Rev. 1.0 11
triggers an under-run interrupt for QUE 2 if the previous frame has not been completed. This has the
effect of aborting the previous frame.
The driver should assign a unique ID number to each transmitted frame. Since the frame does not
include padding or an FCS, make sure the PCWR Append CRC bit is set and the PCWR Disable
Padding bit is clear.
STEP 5: Write to QUE 2 PSZR.
Writing to PSZR indicates to the QUE 2 write logic how many bytes to expect. For example, if the
part is operating in 32-bit bus mode and the byte count is not an even multiple of four, the write logic
uses the size value to determine how many bytes in the last write are valid. If the host attempts to
write an extra word past the end of the programmed size, an overrun interrupt results.
STEP 6: Write the frame data to QUE 2 TDR.
Each successive write to TDR adds the data to QUE 2.
STEP 7: Read the transmit status from TPSR.
Reading TPSR reads status words from the top of a 128 word deep FIFO. One status word is added
to the FIFO for each transmitted frame. If the software does not read the status words for transmitted
frames from the FIFO, it eventually fills to capacity at which time any new status words are dropped
while the FIFO retains the oldest ones.
3.3.3 PAUSE Transmit Immediately
Use the following procedure to cause the immediate transmission of the PAUSE frame:
STEP 1: Read the value of the QUE 2 QSR.
STEP 2: Set the QDR bit in the QSR value.
This can be done using a bit-wise OR operator.
STEP 3: Write the new value back to the QUE 2 QSR.
This sets the QSR QDR bit for QUE 2 and cause the MAC transmitter to select QUE 2 for
transmission of the next frame.
The driver should not set the QSR QDR bit for QUE 2 if no frame has been loaded into QUE 2.
3.4 Local PAUSE
This section describes the procedures used for the automatic local PAUSE timer feature.
3.4.1 Disable Local PAUSE
The default CAM rule set will not activate the local PAUSE timer if the destination MAC address on the
received PAUSE frame is not correct. Disabling the PAUSE MAC address recognition in multicast filter
#1 therefore disables the local PAUSE feature. Use the following procedure to disable local PAUSE:
STEP 1: Disable multicast filter #1 in the CAM.
Modify CAM rule 0x7D (multicast filter #1 byte [0]) to disable the filter.
• Write 0x7D to the CAR Address field.
• Set the RMR Previous Hit Mask field to 0x00.
3.4.2 Enable Local PAUSE
Enabling multicast filter #1 enables the classification engine to automatically identify received PAUSE
frames and set the local PAUSE timer. Use the following procedure to enable local PAUSE: