mirror of
https://github.com/u-boot/u-boot.git
synced 2024-11-26 05:34:30 +08:00
0b1b60c779
Warm reset on OMAP5 freezes when USB cable is connected. Fix requires PRM_RSTTIME.RSTTIME1 to be programmed with the time for which reset should be held low for the voltages and the oscillator to reach stable state. There are 3 parameters to be considered for calculating the time, which are mostly board and PMIC dependent. -1- Time taken by the Oscillator to shut + restart -2- PMIC OTP times -3- Voltage rail ramp times, which inturn depends on the PMIC slew rate and value of the voltage ramp needed. In order to keep the code in u-boot simple, have a way for boards to specify a pre computed time directly using the 'CONFIG_OMAP_PLATFORM_RESET_TIME_MAX_USEC' option. If boards fail to specify the time, use a default as specified by 'CONFIG_DEFAULT_OMAP_RESET_TIME_MAX_USEC' instead. Using the default value translates into some ~22ms and should work in all cases. However in order to avoid this large delay hiding other bugs, its recommended that all boards look at their respective data sheets and specify a pre computed and optimal value using 'CONFIG_OMAP_PLATFORM_RESET_TIME_MAX_USEC' In order to help future board additions to compute this config option value, add a README at doc/README.omap-reset-time which explains how to compute the value. Also update the toplevel README with the additional option and pointers to doc/README.omap-reset-time. Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com> [rnayak@ti.com: Updated changelog and added the README] Signed-off-by: Rajendra Nayak <rnayak@ti.com>
21 lines
811 B
Plaintext
21 lines
811 B
Plaintext
README on how reset time on OMAPs should be calculated
|
|
|
|
CONFIG_OMAP_PLATFORM_RESET_TIME_MAX_USEC:
|
|
Most OMAPs' provide a way to specify the time for
|
|
which the reset should be held low while the voltages
|
|
and Oscillator outputs stabilize.
|
|
|
|
This time is mostly board and PMIC dependent. Hence the
|
|
boards are expected to specify a pre-computed time
|
|
using the above option, (the details on how to compute
|
|
the value are given below) without which a default time
|
|
as specified by CONFIG_DEFAULT_OMAP_RESET_TIME_MAX_USEC
|
|
is used.
|
|
|
|
The value for CONFIG_OMAP_PLATFORM_RESET_TIME_MAX_USEC
|
|
can be computed using a summation of the below 3 parameters
|
|
-1- Time taken by the Osciallator to stop and restart
|
|
-2- PMIC OTP time
|
|
-3- Voltage ramp time, which can be derived using the
|
|
PMIC slew rate and value of voltage ramp needed.
|