PCI2040PGE Datasheet, PDF (59/78 Pages) Texas Instruments – PCI2040 PCI-DSP Bridge Controller

6 DSP HPI Overview
This section gives an overview of the DSP host port interface (HPI). Refer to the C54x/C6x data sheets for complete
HPI details.
6.1 C54X Host Port Interface
The HPI is an 8-bit parallel port used to interface a host device or host processor to a C54x DSP. Information is
exchanged between the DSP and the host device through on-chip C54x memory that is accessible by both the host
and the DSP.
The HPI is designed to interface to the host device as a peripheral, with the host device as the master of the interface,
and so facilitating the ease of access by the host. The host device communicates with the HPI through dedicated
address and data registers, to which the DSP does not have direct access, and the HPI control register using the
external data and interface control signals. Both host devices and the HPI have access to the HPI control register.
In C54x, the HPI provides 16-bit data to the DSP while maintaining an external interface of 8-bit by automatically
combining the successive bytes into 16-bit words. When the host performs a data transfer with the HPI registers, the
HPI control logic automatically performs an access to DSP’s memory to complete the transaction. The DSP can then
access the data within its memory space.
6.1.1 Modes of Operation
In C54x, the HPI has two modes of operation as follows:
• Shared access mode (SAM): This is the normal mode of operation and in this mode both the DSP and
host can access the HPI memory. In this case, the asynchronous host accesses are resynchronized
internally. In the case of a conflict between the DSP and host, host has access priority and DSP waits
1 cycle. In SAM, the HPI can transfer 1 byte every 5 CLKOUT1 (40 MHz), i.e., 64 Mbps. The HPI is
designed such that the host can take advantage of its high bandwidth and can run up to 32 MHz without
requiring wait states.
• Host only mode (HOM): In this mode, only the host can access the HPI memory while the DSP is in reset
state or IDLE2 with all internal or external clocks stopped. This mode allows host to access the HPI
memory while the DSP is in minimum power consumption configuration. In HOM, the HPI supports
higher speed back-to-back accesses on the order of 1 byte/50 ns (160 Mbps) independent of the DSP’s
clock rate.
6.1.2 HPI Functional Description
In C54x, information is exchanged between the host and the DSP via 8-bit external data bus but, because of the 16-bit
word structure of the C54, all transfers consist of two consecutive bytes. The dedicated HWIL pin indicates whether
the first or second byte is being transferred. Bits 0 and 8 (BOB) in the HPI control register determines whether the
first byte is MSB or LSB. The host must not break the first/second byte sequence, otherwise the data may be lost or
some unpredictable results may happen.
6.1.3 HPI Registers
The HPI utilizes three registers for communication between the host device and the CPU. These registers are:
• HPI address register (HPIA). It is directly accessible only by the host and contains the address in HPI
memory at which the current address access occurs.
• HPI control register (HPIC). It is directly accessed by the host or by C54x and contains the control and
status bits for HPI operation.
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