EMBRON Hatteland E Series - Page 114

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RTC Timer (Apollolake) - User Guide
Appendix
IND100077-195
DOC207017- rev 01 – 2018-09-24 - Created by: 6644
Page 6 of 12
Hatteland Display AS, Stokkastrandvegen 87B, N-5578 Nedre Vats, Norway
Tel: (+47) 4814 2200 - mail@hatteland-display.com - www.hatteland-display.com
User Guide RTC Timer - ApolloLake
All intellectual properties belongs to Hatteland Display AS
However, when the system is shutdown or restart, the BIOS firmware has no chance to do the time
copy, then the time of external RTC timer is not up-to-date.
In this case, we need an additional method to update RTC timer under OS, together with PCH time.
So RTC time will always be up-to-date.
This document will introduce the method of accessing RTC timer under OS.
2 Access RTC time
2.1 General Usage
2.1.1 SMBUS Access
The RTC timer is connected to SMBUS interface of processor PCH SMBUS controller. SMBUS I/O
registers are exposed in system IO space. The user can control the I/O register to conduct SMBUS
communication. The SMBUS Base Address is 0xF040 on ApolloLake S/L Board.
To operate read/write operations on SMBUS, the user has to follow the following procedure of writing
data into specific registers.
1. Clear Host Status: Write data 0xFE to offset 0x00, wait the offset 0x00 value changing to
0x40.
2. Set Device address: Write data of address (for RTC timer 0x64(write)/0x65(read)) to offset
0x04
3. Set Slave Device Register Address: Write data of register index on target device to offset 0x03
4. Set Slave Device Register Data (only required for write operation): Write data of register data
on target device to offset 0x05
5. Set Execute bit: Write 0x48 to offset 0x02, and wait for offset 0x02 value change back to
0x08.
6. For read operation, the readout data is available at offset 0x05.
2.1.2 Read Data from RTC timer
Step
Description
IN/OUT
Address
Data
1
Clear Host Status
OUT
Base Address +
0x00
0xFE
2
Wait 1 sec
3
Read Host Status
IN
Base Address +
0x00
4
Wait 1 sec
5
Read Host Status
IN
Base Address +
0x00
(Expect 0x40)
6
Set Device
address
OUT
Base Address +
0x04
0x65
7
Set Slave Device
Register Address
OUT
Base Address +
0x03
0xXX
(See note 1
Time/Date
Register
Definition)
8
Set Execute Bit
OUT
Base Address +
0x02
0x48