This document describes the thermal management process on the Tegra3 chip. It involves monitoring the CPU temperature using sensors, triggering throttling to reduce CPU clock speeds if temperatures exceed a threshold, and shutting down power if temperatures exceed a higher threshold. The process involves drivers, the CPU PMU, and changing the DVFS table to throttle clock speeds until temperatures go back below the limits.

4. Tegra3 Thermal Management cont.
Thermal
Sensor
CPU PMU
Get data from CPU (D+/D-)
Feedback external temperature
Monitoring if temperature is greater
than Throttle threshold
Change power control to reduce
CPU clock and low frequency
Feedback external temperature
Update DVFS table
Get data from CPU (D+/D-)
Notify to start Throttling task

5. Tegra3 Thermal Management cont.
Thermal
Sensor
CPU PMU
Get data from CPU (D+/D-)
Feedback external temperature
Clear DEV_ON bit to prepare to
shutdown power for CPU
Disable peripheral driver
Monitoring if temperature is greater
than Shutdown threshold

6.  Configure IRQ as Low-level trigger.
 HW sends interrupt according to initial threshold stored
in thermal sensor register (FW).

7.  Acer-specific initial value were set as follow:
 Implementation was done in file:
 nct1008.c (Driver layer configuration)
 board-acer-t30.c (NV default value for vendor customization)
 board-acer-t30-sensors.c (set into nct1008 non-violate flash)
Pin Function Threshold
TEMP_ALERT Throttling 85 ℃
AP_OVERHEAT Shutdown 90 ℃

8.  Verification for specific value by commands as follow,
 cat /sys/class/i2c-dev/i2c-4/device/4-004c/tempaerature_alert
 cat /sys/class/i2c-dev/i2c-4/device/4-004c/tempaerature_overheat

9. The ALERT output deasserts only when:
1. Temperature has fallen below the
high temperature limit.
2. Master has read the device address.
3. Cleared the status register.

10. Thermal Sensor
T30
Throttle
node
Monitor
DVFS
Adjust
DVFS
Cooling device N
.
.
.
Cooling device 1
Update
Update
CPU EDP Table
1400/1300/1200/1100
Switch
ALERT
Update
Bind
Monitor
Bind
UpdateUpdate Update

11. nct1008.c
configure_sensor ()
configure_irq ()
get_temp ()
show_temp ()
set alert ()
show alert ()
work_func ()
SW Code Flow cont.
tegra3_thermal.c
tegra_thermal_alert_unlocked ()
tegra_edp_update_thermal_zone ()
cpu_tegra.c edp.c
tegra3_throttle.c
thermal_sys.c
edp_update_limit ()
tegra_cpu_set_speed
show_throttle
tegra_system_edp
_map[]

12. SW Code Flow cont.
 Thermal threshold initialization
board-acer-t30.c
board-acer-t30-sensors.c

13. SW Code Flow cont.
 HW interrupt triggers work_func to proceed throttling task!
Master has read the
device address
Cleared the
status register

14. SW Code Flow cont.
 Stop charging if throttling starts.
 After finish each throttling call, update temperature to T30.

15. SW Code Flow cont.
 Check if temperature is over
limit stored in EDP table.
 Update index for new
temperature to mapping EDP
table.
 Update CPU rate according to
the temperature which was
reported by nct1008 work
function.
 Adjust and update DVFS
latest setting for CPU clock.

16. SW Code Flow cont.
 Throttle sysfs node is the “answer” for CPU to know when
throttling process ends.
 Sysfs node stores in path:
sys/devices/system/cpu/cpu0/cpufreq/throttle

17. SW Code Flow cont.
 tegra3_throttle.c will report the latest status of throttling process.

18. SW Code Flow cont.
 thermal_sys.c (cooling device) write TRUE/FALSE TO sysfs node
“throttle” to update for tegra3_throttle.c and cpu-tegra.c

19. SW Code Flow cont.
 CPU frequency adjustment mapping table with throttling stage.
 Interrupt will be send to notify when temperature isn’t within limit,
 45~60: 1.3GHz
 60~75: 1.3GHz
 75~85: 1.2GHz
 over 85: 1.1GHz
Stage
Core On (cpu0 to 3)

20. SW Code Flow cont.
 CPU frequency adjustment mapping table

21.  SW verification step

22.  HW verification step
Throttling
Shutdown