HOST INTERFACE (HI)
5 - 36
PORT B
MOTOROLA
tine. The most significant bit (HREQ) of the ISR may be tested by the host processor to
determine if the DSP is the interrupting device and the two least significant bits (RXDF
and TXDE) may be tested to determine the interrupt source (see Figure 5-17). The host
processor interrupt service routine must read or write the appropriate HI register to clear
the interrupt. HREQ is deasserted when1) the enabled request is cleared or masked, 2)
DMA HACK is asserted, or 3) the DSP is reset.
5.3.5.3
Polling
In the polling mode of operation, the HREQ pin is not connected to the host processor and
HACK must be deasserted to insure DMA data or IVR data is not being output on H0-H7
when other registers are being polled.
The host processor first performs a data read transfer to read the ISR (see Figure 5-17)
to determine, whether:
1. RXDF=1, signifying the receive data register is full and therefore a data read
should be performed
2. TXDE=1, signifying the transmit data register is empty so that a data write can
be performed
3. TRDY=1, signifying the transmit data register is empty and that the receive
data register on the DSP CPU side is also empty so that the data written by
the host processor will be transferred directly to the DSP side
4. HF2
•
HF3
≠
0, signifying an application-specific state within the DSP CPU
has been reached, which requires action on the part of the host processor
5. DMA=1, signifying the HI is currently being used for DMA transfers. If DMA
transfers are possible in the system, deactivate HACK prior to reading the ISR
so both DMA data and the contents of ISR are not simultaneously output on
H0- H7
6. If HREQ=1, the HREQ pin has been asserted, and one of the previous five
conditions exists
Generally, after the appropriate data transfer has been made, the corresponding status
bit will toggle.
If the host processor has issued a command to the DSP by writing the CVR and setting
the HC bit, it can read the HC bit in the CVR to determine when the command has been
accepted by the interrupt controller in the DSP’s central processing module. When the
command has been accepted for execution, the interrupt controller will reset the HC bit.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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