Read Access To Hpi With Autoincrement: Hwob - Texas Instruments TMS320C6201 Reference Manual

Host Access Sequences
7.4.3 HPID Read Access With Autoincrement
Table 7–11. Read Access to HPI With Autoincrement: HWOB = 1
Event HD
Host reads HPID ????
1st halfword
Data not ready
Host reads HPID BCDE
1st halfword
Data ready
Host reads HPID 789A
2nd halfword
Prefetch ????
Data not
ready
Prefetch ????
Data ready
Note: A ? in this table indicates the value is unknown.
7-22
The autoincrement feature results in efficient sequential host accesses. For
both HPID read and write accesses, this removes the need for the host to load
incremented addresses into HPIA. For read accesses, the data pointed to by
the next address is fetched immediately after the completion of the current
read. Because the intervals between successive reads are used to prefetch
data, the latency for the next access is reduced. Prefetching also occurs after
a host write of FETCH = 1 to the HPIC register. If the next HPI access is an
HPID read, then the data is not refetched and the prefetched data is sent to
the host. Otherwise, the HPI must wait for the prefetch to finish.
Table 7–11 summarizes a read access with autoincrement. After the first half-
word access is complete (with the rising edge of the first HSTROBE), the ad-
dress increments to the next word, or 80001238h in this example. Assume that
the data at that location is 87654321h. This data is prefetched and loaded into
HPID. Prefetching begins on the rising edge of HSTROBE in the second half-
word read.
Value During Access
HBE[1:0] HR/W HCNTL[1:0]
xx 1
xx 1
xx 1
xx x
xx x
HRDY HHWIL
10 1 0
10 0 0
10 0 1
xx 1 x
xx 0 x
Value After Access
HPIC HPIA HPID
00010001 80001234 ????????
00090009 80001234 789ABCDE
00090009 80001234 789ABCDE
00010001 80001238 789ABCDE
00090009 80001238 87654321