MCF548x Reference Manual, Rev. 3
19-46 Freescale Semiconductor

19.3.3.2.11 Rx FIFO Alarm Register (PCIRFAR)

19 OF_MASK Overflow mask. When this bit is set, the FIFO controller masks the Status Registers OF bit from
generating an error.
18 TXW_MASK Transmit wait condition mask. When this bit is set, the FIFO controller masks the Status
Register’s TXW bit from generating an error. (To help with backward compatibility, this bit is
asserted at reset.)
17–0 Reserved, should be cleared.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
R0000000000000000
W
Reset0000000000000000
1514131211109876543210
R000000000 Alarm
W
Reset0000000000000000
Reg
Addr
MBAR + 0x84CC

Figure 19-44. Rx FIFO Alarm Register (PCIRFAR)

Table 19-43. PCIRFAR Field Descriptions

Bits Name Description
31–7 Reserved, should be cleared.
6–0 Alarm Bits 6-0 are programmable to control a 128-byte FIFO. User writes these bits to set the low level
watermark, which is the point at which the FIFO asserts its request for data emptying to the
Multi-Channel DMA controller. This value is in free bytes. For example, with Alarm = 32 (0x20), the
alarm condition will occur when the FIFO has 32 or less free bytes in it. The alarm, once asserted,
will not negate until the high level mark is reached, when there is GR[2:0] or less bytes remaining
in the FIFO.
Note: The Alarm setting should be programmed to a value greater than or equal to Max_Beats *
4 or else data transfer may stall. The Rx controller waits for enough space to be available in the
FIFO for it to write a burst of Max_Beats * 4 bytes before it will request data from the PCI bus. For
a Max_Beats value of 0(8 beats), Alarm should be programmed to 32 or greater.

Table 19-42. PCIRFCR Field Descriptions (Continued)

Bits Name Description