UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 346 o f 792
NXP Semiconductors UM10237
Chapter 13: LPC24XX USB device controller
9.5 Endpoint realization registers
The registers in this group allow realization and configuration of endpoints at run time.

9.5.1 EP RAM requirements

The USB device controller uses a RAM based FIFO for each endpoint buffer. The RAM
dedicated for this purpose is called the Endpoint RAM (EP_RAM). Each endpoint has
space reserved in the EP_RAM. The EP_RAM space required for an endpoint depends
on its MaxPacketSize and whether it is double buffered. 32 words of EP_RAM are used by
the device for storing the endpoint buffer pointers. The EP_RAM is word aligned but the
MaxPacketSize is defined in bytes hence the RAM depth has to be adjusted to the next
word boundary. Also, each buffer has one word header showing the size of the packet
length received.
The EP_ RAM space (in words) required for the physical endpoint can be expressed as
where dbstatus = 1 for a single buffered endpoint and 2 for double a buffered endpoint.
Table 315. USB Endpoint Interrupt Priority register (USBEpIntPri - address 0xFFE0 C240) bit allocation
Reset value: 0x0000 0000
Bit 31 30 29 28 27 26 25 24
Symbol EP15TX EP15RX EP14TX E 14RX EP13TX EP13RX EP12TX EP12RX
Bit 23 22 21 20 19 18 17 16
Symbol EP11TX EP11RX EP10TX EP10RX EP9TX EP9RX EP8TX EP8RX
Bit 15 14 13 12 11 10 9 8
Symbol EP7TX EP7RX EP6TX EP6RX EP5TX EP5RX EP4TX EP4RX
Bit 7 6 5 4 3 2 1 0
Symbol EP3TX EP3RX EP2TX EP2RX EP1TX EP1RX EP0TX EP0RX
Table 316. USB Endpoint Interrupt Priority register (USBEpIntPri - addre ss 0xF FE0 C240) bit description
Bit Symbol Value Description Re set value
31:0 See
USBEpIntPri
bit allocation
table above
0 The corresponding interrupt is rout ed to the EP_SLOW bit of USBDevIntSt 0
1 The corresponding interru pt is rout ed to the EP_FAST bit of USBDevIntSt
EPRAMspace MaxPacketSize 3+
4
--------------------------------------------------1+
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⎛⎞
dbstatus×=