HOST INTERFACE (HI)
MOTOROLA
PORT B
5 - 39
side of the HI, which requires that the options for interrupts and flags be selected and then
the HI be selected (see Figure 5-20). The second step is for the host processor to clear
the HC bit by writing the CVR, select the data transfer method - polling, interrupts, or DMA
(see Figure 5-21 (d) and Figure 5-23), and write the IVR in the case of a MC680XX Family
host processor. Figure 5-19 through Figure 5-22 provide a general description of how to
initialize the HI. Later paragraphs in this section provide more detailed descriptions for
specific examples.These subsections include some code fragments illustrating how to ini-
tialize and transfer data using the HI.
5.3.6.2
Polling/Interrupt Controlled Data Transfer
Handshake flags are provided for polled or interrupt-driven data transfers. Because the
DSP interrupt response is sufficiently fast, most host microprocessors can load or store
data at their maximum programmed I/O (non-DMA) instruction rate without testing the
handshake flags for each transfer. If the full handshake is not needed, the host processor
can treat the DSP as fast memory, and data can be transferred between the host and DSP
at the fastest host processor rate. DMA hardware may be used with the external host
request and host acknowledge pins to transfer data at the maximum DSP interrupt rate.
The basic data transfer process from the host processor’s view (see Figure 5-15) is for
the host to:
1. Assert HREQ when the HI is ready to transfer data
2. Assert HACK If the interface is using HACK
3. Assert HR/W to select whether this operation will read or write a register
4. Assert the HI address (HA2, HA1, and HA0) to select the register to be read or written
STEP 1
THE DSP CPU INITIALIZES THE DSP SIDE OF
THE HI BY WRITING:
1)
HCR AT X:$FFE8 AND
2)
PBC AT X:$FFE0
STEP 2
THE HOST PROCESOR INITIALIZES THE
HOST SIDE OF THE HI BY WRITING:
1)
ICR AT $0 AND/OR
2)
CVR AT $1 AND/OR
3)
IVR AT $3
Figure 5-19 HI Initialization Flowchart
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Freescale Semiconductor, Inc.
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