N900 Hardware LED

(Hardware)
(use <source> and <code>)
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The [[Nokia N900|N900]] has LP5523 <ref name="lp5523-spec">http://www.national.com/pf/LP/LP5523.html</ref> <ref name="leds-lp5523-driver">http://mxr.maemo.org/fremantle/source/kernel/drivers/leds/leds-lp5523.c</ref>, which has 3 engines like LP5521 but can drive 9 LEDs via a multiplexer which maps each LED to one of the 3 engines. A LED also can be unassigned to any engine, in which case you can control it by writing to the corresponding brightness sysnode) which handles the keyboard and notification LED. (not the [[N900 Hardware Flash Torch|flash LEDs]] and red indicator light next to those, and also not the Infrared-LED used for CIR)
The [[Nokia N900|N900]] has LP5523 <ref name="lp5523-spec">http://www.national.com/pf/LP/LP5523.html</ref> <ref name="leds-lp5523-driver">http://mxr.maemo.org/fremantle/source/kernel/drivers/leds/leds-lp5523.c</ref>, which has 3 engines like LP5521 but can drive 9 LEDs via a multiplexer which maps each LED to one of the 3 engines. A LED also can be unassigned to any engine, in which case you can control it by writing to the corresponding brightness sysnode) which handles the keyboard and notification LED. (not the [[N900 Hardware Flash Torch|flash LEDs]] and red indicator light next to those, and also not the Infrared-LED used for CIR)
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The controller can be programmed via "/sys/class/i2c-adapter/i2c-2/2-0032" (FIXME: is this stable?). In that directory there are three files corresponding to the three channels: engine1_mode, engine2_mode and engine3_mode. Each file "stores" one of "run", "load", "disabled" (it seems that there is another mode "direct" but it doesn't work)(direct mode requires explicit writes to PWM, current and multiplexing registers, which may not be supported in the code...):
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The controller can be programmed via "/sys/class/i2c-adapter/i2c-2/2-0032" (FIXME: is this stable?). In that directory there are three files corresponding to the three channels: <code>engine1_mode</code>, <code>engine2_mode</code> and <code>engine3_mode</code>. Each file "stores" one of <code>run</code>, <code>load</code>, <code>disabled</code> (it seems that there is another mode "direct" but it doesn't work)(direct mode requires explicit writes to PWM, current and multiplexing registers, which may not be supported in the code...):
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* run: The program runs
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* <code>run</code>: The program runs
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* disabled: The channel is disabled - not running
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* <code>disabled</code>: The channel is disabled - not running
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* load: In that state, there are two more files in that directory:  
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* <code>load</code>: In that state, there are two more files in that directory:  
** engine1_LEDs is in the form "0000rgb00" (9 digits, "1" or "0"), where rgb control which LEDs should participate. The 6 "0" in the above pattern correspond to the 6 kbd white LEDs controlled by MCE via engine3, so readout of engine3_leds gives 111100011 ;-)
** engine1_LEDs is in the form "0000rgb00" (9 digits, "1" or "0"), where rgb control which LEDs should participate. The 6 "0" in the above pattern correspond to the 6 kbd white LEDs controlled by MCE via engine3, so readout of engine3_leds gives 111100011 ;-)
** engine1_load accepts a string as specified above (e.g. 9d804000427f0d7f7f007f0042000000). LP5523 has an absolute storage of 96 steps a 16bits, which can dynamically partitioned between the three engines. (ToDo: check if driver supports >16 instructions / machine) (Supports 32-96 steps per engine, dynamically-assigned)
** engine1_load accepts a string as specified above (e.g. 9d804000427f0d7f7f007f0042000000). LP5523 has an absolute storage of 96 steps a 16bits, which can dynamically partitioned between the three engines. (ToDo: check if driver supports >16 instructions / machine) (Supports 32-96 steps per engine, dynamically-assigned)
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Despite the line
Despite the line
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<pre>
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<source lang="c">
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87 #define LP5523_DEFAULT_CURRENT          50 /* microAmps */
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#define LP5523_DEFAULT_CURRENT          50 /* microAmps */
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</pre> suggesting different, the units in there are 0.1mA (100 µA per step is correct). So the driver init default for all LED is 5mA, and mce seems to set current to 0.2mA (value 2 in the led_current sysnode) for B and G, and either to 0.2mA or 0.8mA for R. Probably settings as high as 100 for 10mA are safe for the RGB LED, higher values might destroy the LED. (yes, correct, the RGB could be damaged from heat if set to more than 10 mA on all 3 LEDs)
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</source>
 +
suggesting different, the units in there are 0.1 mA (100 µA per step is correct). So the driver init default for all LED is 5 mA, and mce seems to set current to 0.2 mA (value 2 in the led_current sysnode) for B and G, and either to 0.2 mA or 0.8 mA for R. Probably settings as high as 100 for 10 mA are safe for the RGB LED, higher values might destroy the LED. (yes, correct, the RGB could be damaged from heat if set to more than 10 mA on all 3 LEDs)
NOTE: There must be a delay (how much? The specs of LP5521 mentions it) between writes to sysfs files.
NOTE: There must be a delay (how much? The specs of LP5521 mentions it) between writes to sysfs files.

Revision as of 08:20, 10 August 2010

Hardware

The N900 has LP5523 [1] [2], which has 3 engines like LP5521 but can drive 9 LEDs via a multiplexer which maps each LED to one of the 3 engines. A LED also can be unassigned to any engine, in which case you can control it by writing to the corresponding brightness sysnode) which handles the keyboard and notification LED. (not the flash LEDs and red indicator light next to those, and also not the Infrared-LED used for CIR)

The controller can be programmed via "/sys/class/i2c-adapter/i2c-2/2-0032" (FIXME: is this stable?). In that directory there are three files corresponding to the three channels: engine1_mode, engine2_mode and engine3_mode. Each file "stores" one of run, load, disabled (it seems that there is another mode "direct" but it doesn't work)(direct mode requires explicit writes to PWM, current and multiplexing registers, which may not be supported in the code...):

  • run: The program runs
  • disabled: The channel is disabled - not running
  • load: In that state, there are two more files in that directory:
    • engine1_LEDs is in the form "0000rgb00" (9 digits, "1" or "0"), where rgb control which LEDs should participate. The 6 "0" in the above pattern correspond to the 6 kbd white LEDs controlled by MCE via engine3, so readout of engine3_leds gives 111100011 ;-)
    • engine1_load accepts a string as specified above (e.g. 9d804000427f0d7f7f007f0042000000). LP5523 has an absolute storage of 96 steps a 16bits, which can dynamically partitioned between the three engines. (ToDo: check if driver supports >16 instructions / machine) (Supports 32-96 steps per engine, dynamically-assigned)

After that, when the state is changed to "run", the program will be ran by the controller.

In order for the LEDs to work, the led_current of the appropriate LEDs need to be set to non-zero values. This is accomplished by writing to files LEDs:lp5523:[bgr]/led_current under the same directory. Perhaps (?) not or values are suitable.

Despite the line

#define LP5523_DEFAULT_CURRENT          50 /* microAmps */

suggesting different, the units in there are 0.1 mA (100 µA per step is correct). So the driver init default for all LED is 5 mA, and mce seems to set current to 0.2 mA (value 2 in the led_current sysnode) for B and G, and either to 0.2 mA or 0.8 mA for R. Probably settings as high as 100 for 10 mA are safe for the RGB LED, higher values might destroy the LED. (yes, correct, the RGB could be damaged from heat if set to more than 10 mA on all 3 LEDs)

NOTE: There must be a delay (how much? The specs of LP5521 mentions it) between writes to sysfs files.

Software

References

  1. http://www.national.com/pf/LP/LP5523.html
  2. http://mxr.maemo.org/fremantle/source/kernel/drivers/leds/leds-lp5523.c