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Functional Description
• Rx Buffer Offset
16.3.9.8 CPPI DMA Protocols Supported
Four different type of DMA transfers are supported by the CPPI 4.1 DMA; Transparent, RNDIS, Generic
RNDIS, and Linux CDC. The following sections will outline the details on these DMA transfer types.
16.3.9.8.1 Transparent DMA Transfer
Transparent Mode DMA operation is the default DMA mode where DMA interrupt is generated whenever a
DMA packet is transferred. In the transparent mode, DMA packet size cannot be greater than USB
MaxPktSize for the endpoint. This transfer type is ideal for transfer (not packet) sizes that are less than a
max packet size.
16.3.9.8.1.1 Transparent DMA Transfer Setup
The following will configure all 30 ports/channels for Transparent DMA Transfer type.
Make sure that RNDIS Mode is disabled globally. This allows the application to configure the CPPI DMA
protocol in use to be configured per endpoint need. To disable RNDIS operation, clear RNDIS bit in the
USB Control Registers corresponding to the USB Module (default setting), i.e., CTRL0[RNDIS]=0 and
CTRL1[RNDIS]=0.
Configure the USB0/1 Tx/Rx DMA Mode Registers (USB0/1 TX(RX)MODE0/1) for the Endpoint field in
use is programmed for Transparent Mode, i.e., TXMODE0/1[TXn_MODE] = 00b and
RXMODE0/1[RXn_MODE] = 00b.
16.3.9.8.2 RNDIS DMA Transfer
RNDIS mode DMA is used for large transfers (i.e., total data size to be transferred is greater than USB
MaxPktSize where the MzxPktSize is a multiple of 64 bytes) that requires multiple USB packets. This is
accomplished by breaking the larger packet into smaller packets, where each packet size being USB
MaxPktSize except the last packet where its size is less than USB MaxPktSize, including zero bytes. This
implies that multiple USB packets of MaxPktSize will be received and transferred together as a single
large DMA transfer and the DMA interrupt is generated only at the end of the complete reception of DMA
transfer. The protocol defines the end of the complete transfer by receiving a short USB packet (smaller
than USB MaxPktSize as mentioned in USB specification 2.0). If the DMA packet size is an exact multiple
of USB MaxPktSize, the DMA controller waits for a zero byte packet at the end of complete transfer to
signify the completion of the transfer.
NOTE: RNDIS Mode DMA is supported only when USB MaxPktSize is an integral multiple of 64 bytes.
16.3.9.8.2.1 RNDIS DMA Transfer Setup
If all endpoints in use are desired to operate in RNDIS mode, it is only suffix to configure RNDIS DMA
operation in RNDIS mode at the global level and application can ignore individual endpoint DMA mode
configuration. This is achieved by programming CTRLR0/1[RNDIS] with a ‘1.’
However if DMA mode is required to be configured at the endpoint level, it is required to 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.
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
16.3.9.8.3 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
1749
SPRUH73H–October 2011–Revised April 2013 Universal Serial Bus (USB)
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