USBN9603 National Semiconductor, USBN9603 Datasheet - Page 17

• Manufacturer Part Number: USBN9603
• Description: USBN9603 Universal Serial Bus Full Speed Function Controller with Enhanced DMA Support
• Manufacturer: National Semiconductor

4.0 Direct Memory Access (DMA) Support
4.2 AUTOMATIC DMA MODE (ADMA)
ADMA mode allows CPU independent transfer of large bulk or isochronous data streams to or from the USB bus. The ap-
plications DMA controller together with the ADMA logic inside the USBN9603 have the capability to split a large amount of
data and transfer it in (FIFO size) packets via the USB. In addition, automatic error handling is performed by the USBN9603
in order to minimize firmware intervention. The number of transferred data stream bytes must be of a modulo 64 size. The
maximum amount of data is restricted to 256*64 bytes = 16 Kbytes.
To enable an ADMA transfer, the following steps must be performed:
1. The local CPU programs the DMA controller for fly-by demand mode transfers. In this mode, transfers occur only in re-
2. The DMA address counter is programmed to point to the destination memory block in the local shared memory, and the
3. The ADMA enable bit must be set prior to, or at the same time as the DMA enable bit. The DMA enable bit must be
4. The DMA request enable bit and DMA source bits are set in the USBN9603.The respective endpoint enable bit must
5. The USB host can now perform USB bulk or isochronous data transfers over the USB bus to the receive FIFO or from
See Figures 10 and 11 for the transmit and receive sequences using ADMA mode. See Figures 12 and 13 for the basic
DMA write timing and read timing.
sponse to USBN9603 request via the DRQ pin. The data is read/written from/to the USBN9603 receive/transmit FIFO
and written/read into/from local memory during the same bus transaction.
Byte Count register is programmed with the number of bytes in the block to be transferred. The DMA Count register must
be configured with the number of packets to be received or transmitted. If required, the Automatic Error Handling register
must also be configured at this time.
cleared before enabling ADMA mode.
also be set.
the transmit FIFO in the USBN9603. The USBN9603 performs steps 5 to 7 of the normal DMA mode automatically. The
ADMA is stopped either when the last packet is received or the DMA Count register has reached the value zero.
Microcontroller
Microcontroller
Set up ADMA
Set up ADMA
Transaction
Figure 10. Transmit Operation Using ADMA Mode
Fill FIFO
Figure 11. Receive Operation Using ADMA Mode
DMA
USB
Transaction
Read FIFO
USB
DMA
Transaction
DMA
Fill FIFO
USB
17
(Continued)
Transaction
Read FIFO
DMA
USB
Last
Transaction
DMA
Last
Read FIFO
USB
time
time
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