![Texas Instruments SimpleLink Ethernet MSP432E401Y Technical Reference Manual Download Page 1688](http://html1.mh-extra.com/html/texas-instruments/simplelink-ethernet-msp432e401y/simplelink-ethernet-msp432e401y_technical-reference-manual_10955781688.webp)
Functional Description
1688
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Universal Serial Bus (USB) Controller
DMA Request Mode 0 can be used equally well for Bulk, Interrupt or Isochronous transfers. If the endpoint
is configured for Isochronous transfers, DMA Request Mode 0 should always be selected where DMA is
used. DMA Request Mode 1 is valuable where large blocks of data are transferred to a Bulk endpoint. The
USB protocol requires such packets to be split into a series of packets of the maximum packet size for the
endpoint (512 bytes for high speed, 64 bytes for full speed).
NOTE:
The MAXLOAD field must be set to an even number of bytes for proper interrupt generation
in Mode 1.
DMA Request Mode 1 can be used to avoid the overhead of having to interrupt the processor after each
individual packet; instead, the processor is only interrupted after the transfer has completed. In some
cases, the block of data transferred comprises a predefined number of these packets, that the controlling
software counts through the transfer process. In other cases, the last packet in the series may be less
than the maximum packet size and the receiver may use this short packet to signal the en16d of the
transfer. (If the total size of the transfer is an exact multiple of the maximum packet size, the transmitting
software should send a null packet for the receiver to detect.)
Further information on using DMA for Bulk transfers is given in
. DMA transfers may be
byte, half-word, or word, as required. However, all the transfers associated with one packet (with the
exception of the last) must be of the same width so that the data is consistently byte-, word- or double-
word-aligned. The last transfer may contain fewer bytes than the previous transfers in order to complete
an odd-byte or odd-word transfer.
NOTE:
DMA Requests should be disabled before the DMA Request Mode is changed. In particular,
the DMAMODE bit in the USBTXCSRHn register should not be programmed to zero either
before or in the same cycle as the corresponding DMAEN bit is cleared.
27.3.6.1 DMA Burst Operation
The DMA uses incrementing bursts for transferring data. The burst transfer begins when the USB DMA is
given bus mastership and when the address accesses a new 1-Kb block.
Bursts may be done in increments of 4, 8, 16, or of an unspecified length, depending on how the BRSTM
field is configured in the USBDMACTLn register, the size of the packet being transferred and the location
relative to the next 1-Kb boundary. For example if BRSTM = 0x2, increments of 8 or 4 bursts and bursts of
unspecified length are allowed but not 16-byte bursts. There is no restriction on the BRSTM value for
transfers in either DMA Mode 0 or DMA Mode 1.
Each transfer of a packet is generally a word transfer, but there may be additional byte or half-word
transfers
27.3.6.2 DMA Bus Errors
If a bus error occurs while the DMA controller is accessing memory, the DMA controller immediately
terminates the DMA transfer and interrupts the processor with a bus error by setting the ERR bit in the
USBDMACTLn register.
NOTE:
The generation of the bus error interrupt is not affected by setting the IE bit in the
USBDMACTL register. This bus error interrupt is still generated even if the IE bit is 0.
27.3.6.3 DMA Operation
The DMA may be used in connection with any type of transfer, but it is particularly useful when large
blocks of data are to be transferred through a Bulk endpoint. The USB protocol requires that large data
blocks are transferred by sending a series of packets of the maximum packet size for the endpoint (512
bytes for high speed, 64 bytes for full speed). The last packet in the series may be less than the maximum
packet size. The receiver may use the reception of this short packet to signal the end of the transfer (a