5.14.1 Host To Dsp - Host Interface Action; 5.14.2 Host To Dsp - Host Processor Procedure - Motorola DSP56156 Manual

5.14.1 Host to DSP – Host Interface Action
The following procedure outlines the steps that the HI hardware takes to transfer DMA
data from the Host Data Bus to DSP memory.
1. Assert the Host Request HREQ output pin when the transmit byte registers TXH:TXL
are empty (This always occurs in HOST to DSP DMA mode when TXDE=1).
2. Write the selected Transmit Byte register from the Host Data Bus when the HACK in-
put pin is asserted by the DMA controller. Deassert the HREQ pin.
3. If the highest register address has not been reached (i.e., TXDE=1), postincrement the
DMA address counter to select the next register. Wait until HACK is deasserted then
go to step 1.
4. If the highest register address has been reached ((i.e., TXDE=0), load the DMA ad-
dress counter with the value in HM1 and HM0 and transfer the Transmit Byte Registers
TXH:TXL to the Host Receive Data Register HRX when HRDF=0. This will set
HRDF=1. Wait until HACK is deasserted then go to step 1.
NOTES:
• The DSP to HOST data transfers can occur normally in the channel not used for
DMA except that the HOST must use polling and not interrupts.
• The transfer of data from the TXH:TXL register to the HRX register automatically
loads the DMA address counter from the HM1 and HM0 bits in the DMA HOST to
DSP mode.
The host exception is triggered when HRDF=1. The host exception routine must read the
Host Receive Data Register HRX to clear HRDF. The transfer from step 4 to step 1 will
automatically occur if TXDE=1. Note that the execution of the host exception on HRDF=1
condition will occur after the transfer to step 1 and is independent of the handshake since
it is only dependent on HRDF=1.
5.14.2 Host To DSP – Host Processor Procedure
The following procedure outlines the typical steps that the host processor must take to set-
up and terminate a host to DSP DMA transfer.
1. Setup the external DMA controller source address, direction, byte count and other
control registers. Enable the DMA controller channel.
2. Set TXDE and clear HRDF. This can be done with the appropriate Initialize function.
The host must also initialize the DMA counter in the HI using the Initialize feature.
MOTOROLA
DMA MODE OPERATION
HOST INTERFACE 5 - 19