CPU_ELAN(4)

💖 NAME 💖

okay bestie, this is CPU_ELAN(4) from the i386 Kernel Interfaces Manual, and it's literally all about AMD Elan 520 CPU support. no cap, this page is the Elan girlie's whole personality. 🦋

✨ SYNOPSIS ✨

here's the lineup, verbatim, because we do not mess with the code:

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

and the quick rundown:

• options CPU_ELAN — turns on AMD Elan 520 CPU support.
• options CPU_ELAN_PPS — enables precision timestamping, explained below bestie.
• options CPU_ELAN_XTAL — sets the CPU clock crystal frequency in Hz, together with machdep.elan_freq.
• machdep.elan_gpio_config — the sysctl(8) variable for configuring GPIO pins.
• machdep.elan_freq — the sysctl(8) variable for the CPU clock crystal frequency in Hz; default is 33333333 Hz.
• options CPU_SOEKRIS — adds extra tailoring for Soekris Engineering 45xx embedded computers.

🌸 DESCRIPTION 🌸

The options CPU_ELAN enables support for the AMD Elan 520 CPU. 💅

A device /dev/elan-mmcr exports the MMCR register bank to userland using mmap(2). fancy, right? 💖

The i8254 timer will be adjusted to the slightly unorthodox frequency 1189161 Hz (32768 * 45 * 25 / 31) employed by the Elan. not me doing math in public, but there it is. 😭

A timecounter named “ELAN” is implemented using 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. here's the character lore:

• - means the GPIO is unavailable.
• l (lower-case ell) configures a led(4) device (active low).
• L configures a led(4) device (active high).
• . 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. iykyk. 🎀

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. slay. ⭐

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.

bestie, please notice: this signal is not suitable for calibration. 🙈

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. iconic behavior honestly. 🫶

🦋 SEE ALSO 🦋

• led(4)
• timecounters(4)
• sysctl(8)

⭐ HISTORY ⭐

The CPU_ELAN code first appeared in FreeBSD 4.7. vintage, lowkey. 🌈

👑 AUTHORS 👑

Poul-Henning Kamp <phk@FreeBSD.org>

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okay that's the whole page, bestie — source/version vibes: Debian, dated November 23, 2003, and the page is CPU_ELAN(4). slay, bye 🫶💅