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+# NPCD378
+
+This page describes the [Nuvoton] SuperIO chip that can be found on various [HP]
+mainboards.
+
+As no datasheet is available most of the functions have been reverse engineered and
+might be inacurate or wrong.
+
+## LDNs
+
+```eval_rst
++-------+---------------------------+
+| LDN # | Function                  |
++=======+===========================+
+| 0     | FDC                       |
++-------+---------------------------+
+| 1     | Parallel Port             |
++-------+---------------------------+
+| 2     | Com1                      |
++-------+---------------------------+
+| 3     | Com2 / IR                 |
++-------+---------------------------+
+| 4     | LED and PWR button CTRL   |
++-------+---------------------------+
+| 5     | PS/2 AUX                  |
++-------+---------------------------+
+| 6     | PS/2 KB                   |
++-------+---------------------------+
+| 7     | WDT1                      |
++-------+---------------------------+
+| 8     | HWM                       |
++-------+---------------------------+
+| 0xf   | GPIO                      |
++-------+---------------------------+
+| 0x15  | I2C ?                     |
++-------+---------------------------+
+| 0x1e  | SUSPEND CTL ?             |
++-------+---------------------------+
+| 0x1c  | GPIO ?                    |
++-------+---------------------------+
+```
+
+### LDN0
+
+Follows [Nuvoton]'s default FDC register set. See [NCT6102D] for more details.
+
+### LDN1
+
+Follows [Nuvoton]'s default LPT register set. See [NCT6102D] for more details.
+
+### LDN2
+
+Follows [Nuvoton]'s default COM1 register set. See [NCT6102D] for more details.
+
+### LDN3
+
+Follows [Nuvoton]'s default COM2 register set. See [NCT6102D] for more details.
+
+### LDN4
+
+On most SuperIOs the use of LDN4 is forbidden. That's not the case on NPCD378.
+
+It exposes 16 byte of IO config space to control the front LEDs PWM duty cycle
+and power button behaviour on normal / during S3 resume.
+
+### LDN5
+
+A custom PS/2 AUX port.
+
+### LDN6
+
+Follows [Nuvoton]'s default KBC register set. See [NCT6102D] for more details.
+
+### LDN7
+
+Looks like a WDT.
+
+### LDN8
+
+Custom HWM space. It exposes 256 byte of IO config space.
+See [HWM](#HWM) for more details.
+
+## HWM
+
+### Register
+
+The registers are accessible via IO space and are located at LDN8's IOBASE.
+
+```eval_rst
++---------------+-----------------------+
+| IOBASE offset | Register              |
++---------------+-----------------------+
+| 0x4           | Host Write CTRL       |
++---------------+-----------------------+
+| 0x10 - 0xfe   | HWM Page #            |
++---------------+-----------------------+
+| 0xff          | Page index select     |
++---------------+-----------------------+
+```
+
+### Host Write CTRL
+Bit 0 must be cleared prior to writing any of the HWM register and it must be
+set after writing to HWM register to signal the SuperIO that data has changed.
+Reading register is possible at any time and doesn't need special locking.
+
+### HWM Page
+The SuperIO exposes 16 different pages. Nearly all registers are unknown.
+
+**Page 1**
+
+```eval_rst
++---------------+-----------------------+
+| IOBASE offset | Register              |
++---------------+-----------------------+
+| 0x98          | PSU fan PWM           |
++---------------+-----------------------+
+```
+
+### Page index
+The 4 LSB of the page index register selects which HWM page is active.
+A write takes effect immediately.
+
+[NCT6102D]: https://www.nuvoton.com/resource-files/NCT6102D_NCT6106D_Datasheet_V1_0.pdf
+[Nuvoton]: http://www.nuvoton.com/hq/
+[HP]: https://www.hp.com/