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To configure RNDIS DMA mode use, configure the field that correspond to the USB module endpoint
using the corresponding USB0/1 TX(RX) Mode Register, i.e., TXMODE0/1[TXn_MODE] = 01b and
RXMODE0/1[RXn_MODE] = 01b
20.4.8.3 Generic RNDIS DMA Transfer
Generic RNDIS DMA transfer mode is identical to the normal RNDIS mode in nearly all respects,
except for the exception case where the last packet of the transfer can either be a short packet or the
MaxPktSize. When the last packet size is equal to the MaxPktSize then no additional zero-byte packet
is sent when using Generic RNDIS transfer. Generic RNDIS transfer makes use of a USB0/1 GENERIC
RNDIS EPn Size register (there exists a register for each endpoint) that must be programmed with the
transfer size (in bytes) of the transfer for the USB Module (USB0 or USB1) prior to posting a transfer
transaction. If the transfer size is an integer multiple of USB MaxPktSize then no additional zero-byte
packet is sent when using Generic RNDIS transfer. However, if the a short packet has been sent prior
to programmed size count, the transfer would end in a similar fashion an RDIS transfer would behave.
For example, it the USB MaxPktSize (Tx/RxMaxP) is programmed with a value of 64, the Generic
RNDIS EP Size register for that endpoint must be programmed with a value that is an integer multiple
of 64 (for example, 64, 128, 192, 256, etc.) for it behave differently than RNDIS transfer. In other words,
when using Generic RNDIS mode and the DMA is tasked to transfer data transfer size that is less or
equal the size value programmed within the USB0/1 GENERIC RNDIS EPn Size register.
This means that Generic RNDIS mode will perform data transfer in the same manner as RNDIS mode,
closing the CPPI packet if a USB packet with a size less than the USB MaxPktSize size value is
received. Otherwise, the packet will be closed when the value in the Generic RNDIS EP Size register is
reached.
Using USB0/1 GENERIC RNDIS EPn Size register, a packet of up to 64K bytes (65536 bytes) can be
transferred. This is to allow the host software to program the USB module to transfer data that is an
exact multiple of the USB MaxPktSize (Tx/RxMaxP programmed value) without having to send an
additional short packet to terminate.
NOTE: As in RNDIS mode, the USB max packet size (Tx/RxMaxp programmed value) of any Generic
RNDIS mode enabled endpoints must be a multiple of 64 bytes. Generic RNDIS acceleration should
not be enabled for endpoints where the max packet size is not a multiple of 64 bytes. Only transparent
mode should be used for such endpoints.
20.4.8.3.1 Generic RNDIS DMA Transfer Setup
Disable the use of RNDIS at the global level, this is achieved by clearing RNDIS bit field
(CTRLR0/1[RNDIS]=0), since global configuration over-rides endpoint configuration.
Configure the field that correspond to the USB module endpoint using the corresponding USB0/1
TX(RX) Mode Register, i.e., TXMODE0/1[TXn_MODE] = 11b and RXMODE0/1[RXn_MODE] = 11b.
20.4.8.4 Linux CDC DMA Transfer
Linux CDC DMA transfer mode acts in the same manner as RNDIS packets, except for the case where
the last data matches the max USB packet size requiring additional zero-byte packet transfer in RNDIS
mode and this is not the case for Linux CDC. If the last data packet of a transfer is a short packet
where the data size is greater than zero and less the USB MaxPktSize, then the behavior of the Linux
CDC DMA transfer type is identical with the RNDIS DMA transfer type. The only exception is when the
short packet length terminating the transfer is a Null Packet. In this case, instead of transferring the Null
Packet, it will transfer a data packet of size 1 byte with the data value of 00h.
In transmit operation, if an endpoint is configured or CDC Linux mode, upon receiving a Null Packet
from the CPPI DMA, the XFER DMA will then generate a packet containing 1 byte of data, whose value
is 00h, indicating the end of the transfer. During receive operation, the XFER DMA will recognize the
one byte zero packet as a termination of the data transfer, and sends a block of data with the EOP
indicator set and a byte count of one to the CPPI DMA controller. The CPPI DMA realizing the end of
the transfer termination will not update/increase the packet size count of the Host Packet Descriptor.
SPRUGX9 – 15 April 2011
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Preliminary
Communications Port Programming Interface (CPPI) 4.1 DMA
© 2011, Texas Instruments Incorporated
1811
Universal Serial Bus (USB)
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