Usb Udca Head Register (Usbudcah - 0Xe009 0080) - Philips LPC214 Series User Manual

Philips Semiconductors
Volume 1

14.8.14 USB UDCA Head register (USBUDCAH - 0xE009 0080)

The UDCA (USB Device Communication Area) Head register maintains the address
where UDCA is allocated in the USB RAM
system memory which is used for the USB purposes. It is located at address
0x7FD0 0000 and is 8 kB in size. Note, however, DMA on endpoint 0 is not feasible. The
UDCA has to be aligned to 128 - byte boundary and should be of size 128 bytes (32
words that correspond to 32 physical endpoints). Each word can point to a DMA
descriptor of a physical endpoint or can point to NULL (i.e. zero value) when the endpoint
is not enabled for DMA operation. This implies that the DMA descriptors need to be
created only for the DMA enabled endpoints. Gaps can be there while realizing the
endpoints and there is no need to keep dummy DMA descriptors. The DMA engine will not
process the descriptors of the DMA disabled endpoints. The reset value for this register is
0. Refer to
operation" on page 234
read/write register.
Table 210: USB UDCA Head register (USBUDCAH - address 0xE009 0080) bit description
Bit Symbol
6:0 -
31:7 UDCA_Header
The DMA Request Set register is normally used for the test purpose. It is also useful in the
normal operation mode to avoid a "lock" situation if the DMA is programmed after that the
USB packets are already received. Normally the arrival of a packet generates an interrupt
when it is completely received. This interrupt is used by the DMA to start working. This
works fine as long as the DMA is programmed before the arrival of the packet (2 packets -
if double buffered). If the DMA is programmed "too late", the interrupts were already
generated in slave mode (but not handled because the intention was to use the DMA) and
when the DMA is programmed no interrupts are generated to "activate" it. In this case the
usage of the DMA Request Set register is useful to manually start the DMA transfer.
UDCA
UDCA Head
Register
Fig 52. UDCA Head register and DMA descriptors
9397 750 XXXXX
User manual
Section 14.10 "DMA descriptor" on page 230
for more details on DMA descriptors. The USBUDCAH is a
Description
UDCA header is aligned in 128-byte boundaries.
Start address of the UDCA Header.
NULL
0
NULL
1
Next_DD_pointer
2
DDP-EP2
NULL
16
DDP-EP16 Next_DD_pointer
31
DDP-EP31
Rev. 01 — 15 August 2005
(Figure
Next_DD_pointer
DD-EP2-a DD-EP2-b
Next_DD_pointer
DD-EP16-a DD-EP16-b
UM10139
Chapter 14: USB Device Controller
52). The USB RAM is part of the
and Section 14.11 "DMA
Reset value
0x00
0
Next_DD_pointer
DD-EP2-c
NULL
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
NULL
216