Data 1
UHPI_HCS
HSTRB
UHPI_HR/W
UHPI_HCNTL[1:0]
UHPI_HD[15:0]
UHPI_HRDY
UHPI_HHWIL
Internal
Valid
00
Valid
Architecture
967
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Host Port Interface (HPI)
21.2.6.8 Single-Halfword HPIC Cycle
shows the special case (see
) when the host performs a single-halfword cycle
to access the HPIC. The state of UHPI_HHWIL is ignored and if a dual-halfword access is performed, then
the same HPIC register is accessed twice.
Figure 21-6. Multiplexed-Mode Single-Halfword HPIC Cycle (Read or Write)
21.2.6.9 Hardware Handshaking Using the HPI-Ready (UHPI_HRDY) Signal
The HPI uses its ready signal, UHPI_HRDY, to tell the host whether it is ready to complete an access.
During a read cycle, the HPI is ready (UHPI_HRDY is low) when it has data available for the host. During
a write cycle, the HPI is ready (UHPI_HRDY is low) when it is ready to latch data from the host. If the HPI
is not ready, it can drive UHPI_HRDY high to insert wait states. These wait states indicate to the host that
read data is not yet valid (read cycle) or that the HPI is not ready to latch write data (write cycle). The
number of wait states that must be inserted by the HPI is dependent upon the state of the resource that is
being accessed.
When the HPI is not ready to complete the current cycle (UHPI_HRDY is high), the host can begin a new
host cycle by forcing the HPI to latch new control information. However, once the cycle has been initiated,
the host must wait until UHPI_HRDY goes low before causing a rising edge on the internal strobe signal
(internal HSTRB) to complete the cycle. If internal HSTRB goes high when the HPI is not ready, the cycle
will be terminated with invalid data being returned (read cycle) or written (write cycle).
One reason the HPI may drive UHPI_HRDY high is a not-ready condition in one of its first-in, first-out
buffers (FIFOs). For example, any HPID access that occurs while the write FIFO is full or the read FIFO is
empty may result in some number of wait states being inserted by the HPI. The FIFOs are explained in
.
The following sections describe the behavior of UHPI_HRDY during HPI register accesses. In all cases,
the chip select signal, UHPI_HCS, must be asserted for UHPI_HRDY to go low.