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Netronix MSP430 embedded controller
In older board designs, such as the Kobo Aura (N514/E606F0B), Netronix uses an MSP430 as an embedded controller (EC) which handles several features including poweron/poweroff of the i.MX SoC. The MSP430 is connected via I²C and responds to address 0x43.
There are two register layouts. The new one is detected by the NEWMSP macro,
which checks if the version number is 0xe916. This file documents the old
layout.
| version number | found in device | features used | other remarks |
|---|---|---|---|
d726 |
Kobo Aura | Power, RTC, PWM | Reading the version register appears to be enough to keep the power on |
e916 |
unknown | unknown | uses the new register layout |
f110 |
Tolino Shine 2 HD | PWM | I2C messages aren't ACKed |
Interrupts are signaled through a GPIO line in falling edge mode.
For a register read:
- write one byte, the register address
- read two bytes (treated as a big-endian u16 in the original driver)
For a register write:
- write one byte, the register address
- write two bytes, the register value (also a BE u16 in the original driver)
Even though the driver treats all register accesses as 16 bits wide, only the upper (first) byte is used in many cases. This is the case when this file speaks of 8-bit registers or values.
Reading registers that should be written unfortunately gives bogus results in most cases.
When read as a big-endian u16, this register provides the version number of the
EC. A value of 0xe916 indicates the new register layout, which is not
described in this document.
The time is set by writing 8-bit values into the high bytes of the following registers:
| Register | Description |
|---|---|
| 0x10 | year, zero means 2000 |
| 0x11 | month, one-based |
| 0x12 | day of the month, one-based |
| 0x13 | hour, zero-based |
| 0x14 | minute, zero-based |
| 0x15 | second, zero-based |
| Register | Type | Description |
|---|---|---|
| 0x16 | u8 | hour |
| 0x17 | u8 | minute |
| 0x18 | u8 | set to 0x01 in msp430_auto_power |
| Register | Type | Description |
|---|---|---|
| 0x1b | u8 | alarm offset in seconds, high byte |
| 0x1c | u8 | alarm offset in seconds, low byte |
| Register | High byte | Low byte |
|---|---|---|
| 0x20 | year; zero means 2000 | month, one-based |
| 0x21 | day of the month, one-based | hour, zero-based |
| 0x23 | minute, zero-based | second, zero-based |
- 0xff: "Jospeh 100108 // start ADC"
This 16-bit register contains the battery voltage, in the range 0-1023.
TODO: provide conversion formula
This 16-bit register contains different bits that indicate which interrupts have occurred. It can be read and written.
| Bit value | description |
|---|---|
| 0x0001 | Battery is critically low |
| 0x0002 | only used in dead code |
| 0x0008 | On board E606F0B (Kobo Aura), this bit indicates that the battery is charging (or discharging?) |
| 0x0020 | Battery is critically low (in Tolino Shine source code) |
| 0x8000 | Alarm triggered |
- Write the 8-bit value 0x08 to keep the board powered on, or 0x00 to not keep it powered on.
- On E60632, 0x10 is written to this register, in
msp_poweroff.
- Write the 8-bit value 0xff to reset the board.
- Even reading the register will cause a reset?
On some versions, two PWM outputs are supported (intended for white and red light).
| Register | Type | Description |
|---|---|---|
| 0xa1 | u8 | auto-off timer, high part. set to 0xff when disabling front light auto-off timer |
| 0xa2 | u8 | auto-off timer, low part. set to 0xff when disabling front light auto-off timer |
| 0xa3 | u8 | 0x01: enable PWM, 0x00: disable PWM; 0x02: enable second PWM |
| 0xa4 | u8 | period (8MHz/frequency), low byte |
| 0xa5 | u8 | period (8MHz/frequency), high byte |
| 0xa6 | u8 | duty cycle, low byte |
| 0xa7 | u8 | duty cycle, high byte |
| 0xa8 | u8 | duty cycle of second output, low byte (on boards where FL_PWM=4) |
| 0xa9 | u8 | duty cycle of second output, high byte |
The high bytes should be written first. Changes in period or duty cycle take effect after the low byte is written.
The period and duty cycle can be written in an interleaved fashion (period high, duty cycle high, period low, duty cycle low; tested on firmware version d726).
PWM state can't be read back.
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Writing a duty cycle of 0 sometimes gets the device into a weird state where writing a higher duty cycle doesn't get a PWM-connected LED back to full brightness.
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Sometimes disabling and re-enabling the PWM output (via register 0xa3), without reconfiguring period/duty cycle, results in a blinking pattern (at around 2-10 Hz).
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Disabling/enabling the PWM output multiples times in quick succession seems to upset the EC quite badly, to the point where system reset might not work properly anymore. The EC driver used on the Kobo Aura sleeps after enabling PWM output.