Motorola DSP56012 - Manual (Page 101)

Parallel Host Interface
Host Interface (HI)
MOTOROLA DSP56012 User’s Manual 4-21
4.4.4.7 HI Usage Considerations—DSP Side
Synchronization is a common problem when two asynchronous systems are
connected, and careful synchronization is required when reading multiple-bit
registers that are written by another asynchronous system. The considerations for
proper operation on the DSP CPU side are discussed in the following paragraphs,
and considerations for the host processor side are discussed in
Section 4.4.8.4 HI
Port Usage Considerations—Host Side .
The DMA, HF1, HF0, HCP, HTDE, and HRDF status bits are set or cleared by the
host processor side of the interface. These bits are individually synchronized to the
DSP clock.
Note: The only system problem with reading status occurs if HF1 and HF0 are
encoded as a pair because each of their four combinations (00, 01, 10, and 11)
has significance. There is a small possibility that the DSP will read the status
bits during the transition and receive “01” or “10” instead of “11”. The
solution to this potential problem is to read the bits twice for consensus (see
Section 4.4.8.4 HI Port Usage Considerations—Host Side for additional
information).
4.4.5 HI — Host Processor Viewpoint
The host can access the HI asynchronously by using either polling techniques or
interrupt-based techniques. Separate transmit and receive data registers are
double-buffered to allow the DSP CPU and host processor to transfer data efficiently
at high speed. The HI contains a rudimentary DMA controller, which makes
generating addresses (HOA[2:0]) for the TX/RX registers in the HI unnecessary.
4.4.5.1 Programming Model—Host Processor Viewpoint
The HI appears to the host processor as a memory-mapped peripheral occupying
eight bytes in the host processor address space (see
Figure 4-10 ). These registers can
be viewed as the Interrupt Control Register (ICR), the Interrupt Status Register (ISR),
three Receive/Transmit data registers (RXH/TXH, RXM/TXM, and RXL/TXL), and
two vector registers, the Interrupt Vector Register (IVR) and the Command Vector
Register (CVR). The CVR is a special command register that is used by the host
processor to issue commands to the DSP. These registers can be accessed only by the
host processor; they can not be accessed by the DSP. Host processors can use
standard host processor instructions (e.g., byte move) and addressing modes to
communicate with the HI registers. The HI registers are addressed so that 8-bit
MC6801-type host processors can use 16-bit load (LDD) and store (STD) instructions
for data transfers. The 16-bit MC68000/MC68010 host processor can address the HI
using the special MOVEP instruction for word (16-bit) or long-word (32-bit)