CS5535 datasheet(111/555 Pages) NSC

111 / 555 page

Revision 0.8

111

www.national.com

KEL Functional Description (Continued)

4.9.2

Keyboard Emulation Overview

The purpose of the KEL is to model the legacy 8042 key-

board/mouse controller interfaced via legacy I/O Addresses

060h and 064h (also known as Ports 60 and 64). This hard-

ware and supporting processor System Management

Mode (SMM) software are designed to support systems

that do not have a true PS/2-compatible keyboard and/or

mouse interface, but those that have alternative devices

performing the equivalent function. Generally, the alterna-

tive device is a keyboard or mouse off a USB (Universal

Serial Bus) port, but it need not be. Due to the origins of the

hardware to be explained shortly, this discussion generally

assumes a USB alternative device, but this is not a require-

ment from a hardware perspective.

The KEL closely models the keyboard emulation hardware

detailed in the USB OpenHost Controller Interface specifi-

cation (OHCI). It is specifically designed to be software

compatible with this model. In the USB model, it is part of

the USB “Host Controller”, but is logically separate from it.

The discussion and description that follows is taken from

the OHCI specification, but with modifications to reflect the

Geode CS5535 specific implementation.

To support applications and drivers in non-USB-aware

environments (e.g., DOS), a peripheral subsystem needs

to provide some hardware support for the emulation of a

PS/2 keyboard and/or mouse by their USB equivalents

(alternative devices). For OHCI, this emulation support is

provided by a set of registers that are controlled by code

running in SMM. Working in conjunction, this hardware and

software produces approximately the same behavior-to-

application code as would be produced by a PS/2-compati-

ble keyboard and/or mouse interface.

When data is received from the alternative device, the

emulation code is notified and becomes responsible for

translating the alternative device keyboard/mouse data into

a data sequence that is equivalent to what would be pro-

duced by a PS/2-compatible keyboard/mouse interface.

The translated data is made available to the system

through the legacy keyboard interface I/O Addresses 060h

and 064h. Likewise, when data/control is to be sent to the

alternative device (as indicated by the system writing to the

legacy keyboard interface), the emulation code is notified

and becomes responsible for translating the information

into appropriate data to be sent to the alternative device.

On the PS/2 keyboard/mouse interface, a read of I/O

Address 060h returns the current contents of the keyboard

output buffer; a read of I/O Address 064h returns the con-

tents of the keyboard status register. An I/O write to I/O

Addresses 060h and 064h puts data into the keyboard

input buffer (data is being input into the keyboard sub-

system). When emulation is enabled, reads and writes of

I/O Addresses 060h and 064h are captured in the KEL

HceOutput, HceStatus, and/or HceInput operational regis-

ters.

The KEL described here supports a mixed environment in

which either the keyboard or mouse is implemented as an

alternative device and the other device is attached to a

standard PS/2 interface.

The following sub-sections use the term “alternate device

interrupt”. This is an ASMI or IRQ as appropriate for the

device; for example the USB can generate either an ASMI

or IRQ. The KEL generates a separate ASMI or IRQ.

4.9.3

Theory - Keyboard / Mouse Input

When data is received from the alternative device, the

emulation code is notified with an alternate device interrupt

and translates the keyboard/mouse data into an equivalent

PS/2-compatible sequence for presentation to the applica-

tion software. For each byte of PS/2-compatible data that is

to be presented to the applications software, the emulation

code writes to the HCE_Output register. The emulation

code then sets the appropriate bits in the HCE_Status reg-

ister (normally, OutputFull is set for keyboard data and Out-

putFull

plus

AuxOutputFull

for

mouse

data).

keyboard/mouse

interrupts

are

enabled,

setting

the

HCE_Status register bits causes the generation of an IRQ1

for keyboard data and IRQ12 for mouse data. The emula-

tion code then exits and waits for the next alternate device

interrupt.

When the host CPU exits from SMM, it can service the

pending IRQ1/IRQ12. This normally results in a read from

I/O Address 060h. When I/O Address 060h is read, the

KEL intercepts the access and returns the current contents

of HCE_Output. The KEL also clears the OutputFull bit in

HCE_Status and de-asserts IRQ1/IRQ12.

If the emulation software has multiple characters to send to

the application software, it sets the CharacterPending bit in

the HCE_Control register. This causes the KEL to generate

an ASMI at the beginning of the next frame a time after the

application read from I/O Address 060h (HCE_Output.).

4.9.4

Theory - Keyboard Output

Keyboard output is indicated by application software writing

data to either I/O Address 060h or 064h. Upon a write to

either address, the KEL captures the data in the

HCE_Input register and, except in the case of a FA20#

(Force processor Address bit 20 to zero when low)

sequence, updates the HCE_Status register’s InputFull

and CmdData bits. When the InputFull bit is set, a KEL

ASMI is generated at the beginning of the next frame. Upon

receipt of the KEL ASMI, the emulation software reads

HCE_Control and HCE_Status to determine the cause of

the emulation interrupt and performs the operation indi-

cated by the data. Generally, this means putting out data to

the alternate device.

4.9.5

Emulation Events

Emulation Events (EEs) are caused by reads and writes of

the emulation registers. EEs generated by the emulation

hardware are steered by the KEL to either an ASMI or an

Emulation Interrupt. Steering is determined by the EE

Routing (EER) bit of the Keyboard Emulation Logic Control

Historically, EEs for data coming from the keyboard/mouse

are generated on USB frame boundaries. The KEL is inde-

pendent of the USB logic, but uses USB frame boundaries

for backward compatibility. Alternately, an independent 1

CS5535 Datasheet(PDF) 111 Page - National Semiconductor (TI)

CS5535 Datasheet(HTML) 111 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Descarga

Enlace URL