WM8310GEB/V Wolfson Microelectronics, WM8310GEB/V Datasheet - Page 128

• Manufacturer Part Number: WM8310GEB/V
• Description: POWER MANAGEMENT SUBSYSTEM, 169BGA
• Manufacturer: Wolfson Microelectronics

Specifications of WM8310GEB/V

• Supply Voltage: 7V
• No. Of Step-down Dc - Dc Converters: 4
• No. Of Ldo Regulators: 11
• Digital Ic Case Style: BGA
• No. Of Pins: 169
• No. Of Regulated Outputs: 13
• Operating Temperature Range: -40°C To
• Rohs Compliant: Yes
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

WM8310
20.4 DIGITAL RIGHTS MANAGEMENT
20.5 BACKUP MODE CLOCKING OPTIONS
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The Real Time Clock (RTC) maintains a continuous record of the time; this is maintained at all times,
including when the WM8310 is powered down and the RTC function is maintained by the backup
battery.
It is highly desirable to be able to write to the RTC counter in order to configure it for logical
translation into hours/minutes and to support calendar functions. However, for digital rights
management purposes, it is important that malicious modification of the RTC is either prevented or
detected.
The security measure implemented on the WM8310 is the RTC Write Counter. This register is
initialised to 0000h during Power On Reset, and is updated automatically whenever a Write operation
is scheduled on either of the RTC_TIME registers. Note that, when the RTC Write Counter is
updated, the new value is generated at random; it is not a sequential counter.
It is assumed that legitimate updates to the RTC_TIME are only those initiated by the Application
Processor (AP). When the AP makes an update to the RTC_TIME, the AP can also read the new
value of the RTC Write Counter, and should store the value in non-volatile memory. If the AP detects
a change in value of the RTC Write Counter, and this was not caused by the AP itself writing to the
RTC_TIME, this means that an unauthorised write to the RTC_TIME registers has occurred.
In order to make it difficult for an unauthorised RTC_TIME update to be masked by simply writing to
the RTC Write Counter, the RTC_WR_CNT field is generated at random by the WM8310 whenever
the RTC_TIME field is updated.
For additional security, the WM8310 does not allow the RTC to be updated more than 8 times in a
one-hour period. Additional write attempts will be ignored.
The RTC Control registers are described in Table 70.
The BACKUP state is entered when the available power supplies are below the reset threshold of the
device. Typically, this means that USB or Wall supplies are not present and that the main battery is
either discharged or removed. Most of the device functions and registers are reset in this state.
The RTC and oscillator and a ‘software scratch’ memory area can be maintained from a backup
power source in the BACKUP state. This can either be a rechargeable battery (coin cell or
super/gold-capacitor) on the BACKUPVDD pin or else a standard capacitor on the LDO12VOUT pin.
The RTC and oscillator can be disabled in the BACKUP state by setting the XTAL_BKUPENA
register bit to 0. This feature may be used to minimise the device power consumption in the BACKUP
state. A 22μF capacitor connected to LDO12VOUT can maintain the RTC value, unclocked, for up to
5 minutes in BACKUP if the oscillator is disabled.
The XTAL_BKUPENA register bit is defined in Section 13.1. For more details on backup power, see
Section 17.6.
PP, December 2009, Rev 3.0
Pre-Production
128