Host Access Sequences
7-20
Table 7–8. Initialization of HWOB = 0 and HPIA
Value During Access
Value After Access
Event
HD
HBE[1:0]
HR/W
HCNTL[1:0]
HHWIL
HPIC
HPIA
HPID
Host writes HPIC
1st halfword
0000
xx
0
00
0
00080008
????????
????????
Host writes HPIC
2nd halfword
0000
xx
0
00
1
00080008
????????
????????
Host writes HPIA
1st halfword
8000
xx
0
01
0
00080008
8000????
????????
Host writes HPIA
2nd halfword
1234
xx
0
01
1
00080008
80001234
????????
Note:
A ? in this table indicates the value is unknown.
7.4.2
HPID Read Access Without Autoincrement
Assume that once the HPI is initialized, the host wishes to perform a read ac-
cess to an address without an autoincrement. Assume that the host wants to
read the word at address 80001234h and that the word value at that location
is 789ABCDEh. Table 7–9 and Table 7–10 summarize this access for HWOB
= 1 and HWOB = 0, respectively. On the first halfword access, the HPI waits
for any previous requests to finish. During this time, HRDY pin is held high.
Then, the HPI sends the read request to the DMA auxiliary channel. If no pre-
vious requests are pending, this read request occurs on the falling edge of
HSTROBE. HRDY pin remains high until the DMA auxiliary channel loads the
requested data into HPID. Because all DMA auxiliary channel reads are word
reads, at the beginning of the second read access, the data is already present
in HPID. Thus, the second halfword HPID read never encounters a not-ready
condition, and HRDY pin remains active. The byte enables are not important
in this instance, because the HPI performs only word reads.