Datasheet

6−2

• HPI data register (HPID). This register is directly accessible by the host and contains the data that was

read from the HPI memory if the current access is a read, or the data that will be written to the HPI

memory if the current access is a write.

The two control inputs, HCNTL1 and HCNTL0, indicate which internal register is being accessed as shown below.

Table 6−1. C54X HPI Registers Access Control

HCNTL1 HCNTL0 DESCRIPTION

0 0 PCI2040 read/write to HPI control register.

0 1

PCI2040 read/write to HPI data register. Address auto-increment is

selected.

1 0 PCI2040 read/write to HPI address register.

1 1

PCI2040 read/write to HPI data register. Address auto-increment is

not selected.

HPI control register is a 16-bit register but only 4 bits control the HPI operation. Because the transfer consists of two

consecutive half-words, the HPI control register is organized such that it has the same high and low half-word

contents. The control and status bits are located on the least significant 4 bits. When the host writes to the HPI control