![Texas Instruments AM1808 Скачать руководство пользователя страница 973](http://html.mh-extra.com/html/texas-instruments/am1808/am1808_technical-reference-manual_1094558973.webp)
Architecture
973
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Host Port Interface (HPI)
21.2.6.10.2 Write Bursting
A write to the write address register (HPIAW) causes the write FIFO to be flushed. This means that any
write data in the write FIFO is forced to its destination in the processor memory (the HPI DMA logic
performs burst operations until the write FIFO is empty). When the FIFO has been flushed, the only action
that will cause the HPI DMA logic to perform burst writes is a host write to HPID with autoincrementing.
The initial host-write data is stored in the write FIFO. An HPI DMA write is not requested until there are
four words in the write FIFO. As soon as four words have been written to the FIFO via HPID write cycles
with autoincrementing, the HPI DMA logic performs a 4-word burst operation to the processor memory.
The burst operations continue as long as there are at least four words in the FIFO. If the FIFO becomes
full (eight words are waiting in the FIFO), the HPI holds off the host by deasserting UHPI_HRDY until at
least one empty word location is available in the FIFO.
Because excessive time might pass between consecutive burst operations, the HPI has a time-out
counter. If there are fewer than four words in the write FIFO and the time-out counter expires, the HPI
DMA logic empties the FIFO immediately by performing a 2-word or 3-word burst, or a single-word write,
as necessary. Every time new data is written to the write FIFO, the time-out counter is automatically reset
to begin its count again. The time-out period is set to a value of 160. For more detailed information about
the time-out period, see your device-specific data manual.
NOTE:
An HPID write cycle without autoincrementing does not initiate any bursting activity. Instead,
it causes the write FIFO to be flushed and causes the HPI DMA logic to perform a single-
word write to the processor memory. As soon as the host activates a write cycle without
autoincrementing, bursting activity ceases until the occurrence of an autoincrement write
cycle. A nonautoincrement write cycle always should be preceded by the initialization of
HPIAW or by another nonautoincrement access, so that the write FIFO is flushed
beforehand.