User guide

DS3134

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Done Queue FIFO Flush Timer

To make sure that the Done Queue FIFO does get flushed to the Done Queue on a regular basis, the

Receive Done Queue FIFO Flush Timer (RDQFFT) is used by the DMA to determine the maximum wait

time in between writes. The RDQFFT is a 16-bit programmable counter that is decremented every PCLK

divided by 256. It is only monitored by the DMA when the Receive Done Queue FIFO is enabled

(RDQFE = 1). For a 33 MHz PCLK, the timer is decremented every 7.76 us and for a 25 MHz clock it is

decremented every 10.24 us. Each time the DMA writes to the Done Queue it resets the timer to the

count placed into it by the Host. On initialization, the Host will set a value into the RDQFFT that

indicates the maximum time the DMA should wait in between writes to the Done Queue. For example,

with a PCLK of 33 MHz, the range of wait times are from 7.8 us (RDQFFT = 0001h) to 508 ms

(RDQFFT = FFFFh) and PCLK of 25 MHz, the wait times range from 10.2 us (RDQFFT = 0001h) to 671

ms (RDQFFT = FFFFh).

76543210

TC7 TC6 TC5 TC4 TC3 TC2 TC1 TC0

15 14 13 12 11 10 9 8

TC15 TC14 TC13 TC12 TC11 TC10 TC9 TC8

Note: Bits that are underlined are read only, all other bits are read-write; default value for all bits is 0.

Bits 0 to 15 / Receive Done Queue FIFO Flush Timer Control Bits (TC0 to TC15). Please note that

on system reset, the timer will be set to 0000h which is defined as an illegal setting. If the Receive Done

Queue FIFO is to be activated (RDQFE = 1), then the Host must first configure the timer to a proper state

and then set the RDQFE bit to one.

0000h = illegal setting

0001h = Timer Count Resets to 1

FFFFh = Timer Count Resets to 65536

76543210

n/a n/a RDQF RDQFE RFQSF RFQLF n/a RFQFE

15 14 13 12 11 10 9 8

n/a n/a n/a n/a n/a RDQT2 RDQT1 RDQT0

Note: Bits that are underlined are read only, all other bits are read-write; default value for all bits is 0.

Bit 0 / Receive Free Queue FIFO Enable (RFQFE). See Section 8.1.3 for details.

Bit 2 / Receive Free Queue Large Buffer FIFO Flush (RFQLF). See Section 8.1.3 for details.

Bit 3 / Receive Free Queue Small Buffer FIFO Flush (RFQSF). See Section 8.1.3 for details.