Architecture
1554
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Universal Parallel Port (uPP)
32.2.8.3 Internal Bus Error (ERR) Event
This event occurs when the uPP peripheral or its internal DMA controller encounters an internal bus error.
After encountering this error, the uPP peripheral should be reset to avoid further problem.
32.2.8.4 Underrun or Overflow (UOR) Event
This event occurs when the DMA channel fails to keep up with incoming or outgoing data on its
associated interface channel. Typically, this error indicates that background system activity has interfered
with normal operation of the peripheral. It does not occur simply when a channel is allowed to idle. After
encountering this error, the uPP peripheral should be reset when this event occurs.
This error should primarily occur when operating the uPP at high speed with significant system loading. To
avoid this error, run the uPP at slower speeds or reduce background activity, such as non-uPP peripheral
or DMA transactions. Additional tuning tips are given in
32.2.8.5 DMA Programming Error (DPE) Event
This event occurs when the DMA channel descriptors are programmed while its PEND bit in the uPP DMA
channel status register (UPxS2) is set to 1. A channel’s descriptors should only be programmed while the
channel's PEND bit is cleared to 0.
32.2.9 Power Management
The uPP peripheral can be placed in reduced-power modes to conserve power during periods of inactivity.
For information on power management, see the
Power Management
chapter.
32.2.10 Emulation Considerations
The uPP peripheral stops running if any of three conditions are met:
•
Peripheral Disable – EN bit in the uPP peripheral control register (UPPCR) is 0.
•
Clock Stop – uPP acknowledges a clock stop request from the device power management module.
•
Emulation Suspend – JTAG emulator halts chip while FREE = 0 and SOFT = 1 in UPPCR.
For other settings of FREE and SOFT, the uPP peripheral continues running during emulation halt.
When the uPP encounters a stop condition, it completes the current DMA burst transaction (if one is
active) before stopping.
An I/O channel configured in transmit mode immediately places its pins in a high-impedance state and
preserves the state of its internal state machines. Unless some reset event occurs (see
the channel can resume where it left off when the stop condition is cleared.
An I/O channel configured in receive mode immediately asserts its WAIT signal (see
) and
captures one additional data word. Further incoming data words are ignored as long as the stop condition
persists.
32.2.11 Transmit and Receive FIFOs
Each of the uPP peripheral I/O channels has a 512-byte FIFO. In receive mode, the FIFO is divided into
eight 64-byte blocks. In transmit mode, the FIFO is divided into blocks that can be set to 64, 128, or 256
bytes, configured by the TXSIZEA or TXSIZEB field in the uPP threshold configuration register (UPTCR).
Transmission will not begin until the channel has loaded enough data to fill at least one full FIFO block.
The internal DMA channels may also be configured to use a read threshold of 64, 128, or 256 bytes using
the RDSIZEI or RDSIZEQ field in UPTCR. The DMA write threshold is fixed at 64 bytes.