Servicing the Host Interface
MOTOROLA
Host Interface Eight (HI8)
16-31
Preliminary
16
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 DSP-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-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 Steps 4 to 1 is
automatic if TXDE = 1.
Note:
The execution of the Host exception on HRDF = 1 condition occurs after the
transfer to Step 1 and is independent of the handshake since it is only dependent
on HRDF = 1.
16.10.9.2
Host-to-DSP Host Processor Procedure
The following procedure outlines the typical steps that the Host Processor must take to
setup 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. The DSP must be configured to handle the incoming Host data via polling,
interrupts, or DSP Side DMA configuration. If interrupt operation is desired HRIE
must be set to enable the HRDF interrupt. If DSP Side DMA operations are desired,
set RDMAE to enable DSP transfers when HRDF is set. This could be done with a
separate Host Command exception routine in the DSP.
3. Set TXDE and clear HRDF. This can be done with the appropriate Initialize
function. The Host must also initialize the DMA counter in the HI8 using the
initialize feature. HREQ output pin is asserted immediately by the DSP hardware
which begins the DMA transfer.
4. Perform other tasks until interrupted by the DMA controller DMA complete
interrupt. The DSP Interface Control Register (ICR), the Interrupt Status Register