Texas Instruments TMS320C6457 manual FIFOs and Bursting, Read Bursting

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6FIFOs and Bursting

The HPI data register (HPID) is a port through which the host accesses two first-in, first-out buffers (FIFOs). As shown in Figure 28, a read FIFO supports host read cycles, and a write FIFO supports host write cycles. Both read and write FIFOs are 8-words deep (each word is 32 bits). If the host is performing multiple reads or writes to consecutive memory addresses (autoincrement HPID cycles), the FIFOs are used for bursting. The HPI DMA logic reads or writes a burst of four words at a time when accessing one of the FIFOs.

Bursting is essentially invisible to the host because the host interface signaling is not affected. Its benefit to the host is that the HRDY signal is deasserted less often when there are multiple reads or writes to consecutive addresses.

Figure 28. FIFOs in the HPI

Write FIFO control logic

Host write pointer

Host writes

Write FIFO

Read FIFO

Host reads

HPI DMA read pointer

HPI DMA logic

Burst writes

Burst reads

Switched

central

resource

DSP

internal/ external memory

Host read pointer

HPI DMA write pointer

Read FIFO control logic

6.1Read Bursting

When the host writes to the read address register (HPIAR), the read FIFO is flushed. Any host read data that was in the read FIFO is discarded (the read FIFO pointers are reset). If an HPI DMA write to the read FIFO is in progress at the time of a flush request, the HPI allows this write to complete and then performs the flush.

After any read FIFO flush, no read cycles are being initiated. Read bursting can begin in one of two ways: the host initiates an HPID read cycle with autoincrementing, or the host initiates issues a FETCH command (writes 1 to the FETCH bit in HPIC).

32 Host Port Interface (HPI) SPRUGK7A –March 2009 –Revised July 2010

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