CPU_ELAN(4)

📦 version 12.2, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu questing, ubuntu resolute, ubuntu stonking

💖 NAME 💖

CPU_ELAN — bestie, it's giving AMD Elan 520 CPU support 💅 (and yes, this is the i386 Kernel Interfaces Manual, you're in the right place, iykyk)

🎀 SYNOPSIS 🎀

options CPU_ELAN
options CPU_ELAN_PPS
options CPU_ELAN_XTAL
machdep.elan_gpio_config
machdep.elan_freq
options CPU_SOEKRIS

👑 DESCRIPTION 👑

okay so. The options CPU_ELAN turns on support for the AMD Elan 520 CPU. iconic, no notes. ✨

A device /dev/elan-mmcr exports the MMCR register bank to userland using mmap(2). lowkey obsessed with that.

The i8254 timer will be adjusted to the slightly unorthodox frequency 1189161 Hz (32768 * 45 * 25 / 31) employed by the Elan. not me doing multiplication in public but she ate that.

A timecounter named “ELAN” is implemented using the general purpose timer 2, but it will not be usable unless HZ is configured at 150 or higher. 🚨 This timecounter is much better than the “i8254” timecounter and should be used at all times. periodt.

The machdep.elan_gpio_config sysctl(8) variable enables configuration of the GPIO pins of the CPU. The string must be exactly 32 characters long, fr fr, don't try to be cute about it. The characters mean:

  • A - means the GPIO is unavailable. 💀
  • A l (lower-case ell) configures a led(4) device (active low). 🌸
  • A L configures a led(4) device (active high). 🔥
  • A . means no configuration for this GPIO. 🙈

These led(4) devices will be named /dev/led/gpio%d. For meaning of P, e and E, see under options CPU_ELAN_PPS. 👀

The options CPU_ELAN_XTAL and the machdep.elan_freq sysctl(8) variable can be used to set the CPU clock crystal frequency in Hz. The default is 33333333 Hz. ✨

The options CPU_ELAN_PPS enables precision timestamping using the RFC2783 PPS-API via the /dev/elan-mmcr device. The resolution will be approximately 125 nsec and the precision ± 125 nsec. (For 125 nsec read “4 / CPU clock crystal frequency”.) 🕰️

The input signal must be connected to the TMR1IN pin and a GPIO pin. The GPIO pin must be configured with a P in machdep.elan_gpio_config.

In addition, one GPIO pin can be configured with either e (active low) or E (active high) to become a “echo” output of the input signal.

🚨 Please notice that this signal is not suitable for calibration. do not do it, bestie, I'm begging.

If the options CPU_SOEKRIS is given, the support will additionally be tailored to the Soekris Engineering 45xx series of embedded computers. The “error” led will be configured (as /dev/led/error) and the GPIO pins which are not available will be disabled. 🫶

🌈 SEE ALSO 🌈

led(4), timecounters(4), sysctl(8)

🦋 HISTORY 🦋

The CPU_ELAN code first appeared in FreeBSD 4.7. vintage core fr. 👑

💜 AUTHORS 💜

Poul-Henning Kamp <phk@FreeBSD.org>

and that's the whole page, babe 🫶 this one shipped with the <strong>Debian</strong> glow-up, dated <strong>November 23, 2003</strong> — go forth and configure your GPIOs responsibly 💅✨

📦 where this page comes from