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Servicing the Host Interface
5685X Digital Signal Controller User Manual, Rev. 4
16-32
Freescale Semiconductor
In the case where the Host Processor is a member of the
MC680XX family
, servicing the interrupt
starts by asserting HREQ to interrupt the processor. The Host Processor then acknowledges the
interrupt by asserting HACK. When HREQ and HACK are simultaneously asserted, the contents
of the IVR are placed on the Host data bus. This vector tells the Host Processor which routine to
use to service the HREQ interrupt.
16.10.9 Host Side DMA Mode Operation
The Host DMA mode allows the transfer of 8-bit or 16-bit data between the DSC HI8 and an
external DMA controller. The HI8 provides the synchronization logic between the two
asynchronous processor systems. The DSC Side of the interface is serviced by any appropriate
servicing mechanism such as polling, interrupts, or DMA transfer.
The external DMA controller provides the transfers between the DSC HI8 registers and the
external DMA memory. The external DMA controller must provide the address to the external
DMA memory. The address of the selected HI8 register is provided by a DMA address counter in
the DSC HI8.
16.10.9.1 Host-to-DSC Host Interface Action
The following four procedure outlines the steps the HI8 hardware takes to transfer DMA data
from the Host data bus to DSC memory.
1. Assert the Host Request HREQ output pin when the transmit byte registers TXH/TXL are
empty. This always occurs in Host-to-DSC DMA mode when TXDE = 1.
2. Write the selected transmit byte register from the Host data bus when the HACK input pin
is asserted by the DMA controller. Deassert the HREQ pin.
3. If the highest register address has not been reached, such as TXDE = 1, post-increment 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, such as TXDE = 0, load the DMA address
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 sets HRDF = 1.
Wait until HACK is deasserted then go to Step 1.
Note:
The DSC-to-Host data transfers can occur normally in the channel not used for DMA
except when the Host must use polling and not interrupts.
Note:
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-DSC mode.