UM10503
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User manual
Rev. 1.3 — 6 July 2012
551 of 1269
NXP Semiconductors
UM10503
Chapter 23: LPC43xx USB0 Host/Device/OTG controller
23.8.1.4 Data structures
The same data structures used for FS/LS transactions though a HS hub are also used for
transactions through the Root Hub with an embedded Transaction Translator. Here it is
demonstrated how the Hub Address and Endpoint Speed fields should be set for directly
attached FS/LS devices and hubs:
1. QH (for directly attached FS/LS device) – Async. (Bulk/Control Endpoints) Periodic
(Interrupt)
–
Hub Address = TTHA (default TTHA = 0)
–
Transactions to directly attached device/hub: QH.EPS = Port Speed
–
Transactions to a device downstream from directly attached FS hub: QH.EPS =
Downstream Device Speed
Remark:
When QH.EPS = 01 (LS) and PORTSC1.PSPD = 00 (FS), a LS-pre-pid
will be sent before transmitting the LS traffic.
Maximum Packet Size must be less than or equal to 64 or undefined behavior may
result.
2. siTD (for directly attached FS device) – Periodic (ISO Endpoint)
all FS ISO transactions:
Hub Address = (default TTHA = 0)
siTD.EPS = 00 (full speed)
Maximum Packet Size must be less than or equal to 1023 or undefined behavior may
result.
23.8.1.5 Operational model
The operational models are well defined for the behavior of the Transaction Translator
(see USB 2.0 specification) and for the EHCI controller moving packets between system
memory and a USB-HS hub. Since the embedded Transaction Translator exists within the
host controller there is no physical bus between the EHCI host controller driver and the
USB FS/LS bus. These sections will briefly discuss the operational model for how the
EHCI and Transaction Translator operational models are combined without the physical
bus between them. The following sections assume the reader is familiar with both the
EHCI and USB 2.0 Transaction Translator operational models.
23.8.1.5.1
Micro-frame pipeline
The EHCI operational model uses the concept of H-frames and B-frames to describe the
pipeline between the Host (H) and the Bus (B). The embedded Transaction Translator
shall use the same pipeline algorithms specified in the USB 2.0 specification for a
Hub-based Transaction Translator.
It is important to note that when programming the S-mask and C-masks in the EHCI data
structures to schedule periodic transfers for the embedded Transaction Translator, the
EHCI host controller driver must follow the same rules specified in EHCI for programming
the S-mask and C-mask for downstream Hub-based Transaction Translators. Once
periodic transfers are exhausted, any stored asynchronous transfer will be moved.
Asynchronous transfers are opportunistic in that they shall execute whenever possible
and their operation is not tied to H-frame and B-frame boundaries with the exception that
an asynchronous transfer can not babble through the SOF (start of B-frame 0.)