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HPI Signal Descriptions
When low, HRDY indicates that the HPI is ready for a transfer to be performed.
HCS enables HRDY, and HRDY is always low when HCS is high. Case 1 in
Figure 7–6 and Figure 7–7, where HRDY goes high when HCS falls, indicates
that the HPI is busy completing a previous HPID write or read with autoincre-
ment.
When the host performs a read access from HPID without autoincrement, the
HPI sends the read request to the DMA auxiliary channel, and HRDY becomes
high. This event occurs with the first falling edge of HSTROBE. HRDY remains
high until the DMA auxiliary channel loads the requested data into HPID. At the
beginning of the second read access, the data is already present in HPID (the
DMA auxiliary channel performs word reads). Thus, the second halfword HPID
read never encounters a not-ready condition, and HRDY remains low.
In the case of HPID read access with autoincrement, the data pointed to by the
next address is fetched immediately after the completion of the current read.
Therefore, after the second halfword transfer of the current read (with the sec-
ond rising edge of HSTROBE), HRDY becomes high again, indicating that HPI
is busy pre–fetching data. During an HPID write access, two halfword portions
of the HPID are transferred from the host. At the end of this write access, HRDY
becomes high (with the second rising edge of HSTROBE), and the contents of
HPID are transferred as a 32-bit word to the address specified by HPIA. Read-
ing or writing to HPIC or HPIA does not affect the HRDY signal.
Host-Port Interface
7-13
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