STRUCT COMEDI_SUBDINFO(9)

📦 version 7.3.1, in nixpkgs unstable

✨ struct comedi_subdinfo(9) ✨

okay bestie, settle in 💅 this is a kernel API manual page for struct comedi_subdinfo, and it's literally the little info packet that tells you everything about a subdevice. no cap, it's giving "backstage pass to the hardware" energy 🎀

🌸 NAME 🌸

struct comedi_subdinfo — used to retrieve information about a subdevice 💖

✨ SYNOPSIS ✨

struct comedi_subdinfo {
    unsigned int type;
    unsigned int n_chan;
    unsigned int subd_flags;
    unsigned int timer_type;
    unsigned int len_chanlist;
    unsigned int maxdata;
    unsigned int flags;
    unsigned int range_type;
    unsigned int settling_time_0;
    unsigned int insn_bits_support;
    unsigned int unused[8];
 };

🦋 Members 🦋

  • type — the subdevice's type, straight from enum comedi_subdevice_type. iykyk 🫶
  • n_chan — how many channels this subdevice supports. the channel headcount fr fr 💖
  • subd_flags — a whole mix of static and dynamic flags describing different aspects of the subdevice plus its current state. it's giving "mood ring but make it bitmasks" 🌈
  • timer_type — the timer type. always set to 5 (the "nanosecond timer"). iconic, consistent, never changes 👑
  • len_chanlist — the maximum length of a channel list, but only if the subdevice supports asynchronous acquisition commands. conditional queen ✨
  • maxdata — the maximum sample value for all channels, whenever the SDF_MAXDATA subdevice flag is clear 🍓
  • flags — channel flags for all channels, whenever the SDF_FLAGS subdevice flag is clear 💜
  • range_type — the range type for all channels, whenever the SDF_RANGETYPE subdevice flag is clear. it encodes three things: the subdevice index (bits 27:24), a dummy channel index 0 (bits 23:16), and the range table length (bits 15:0). she's packed, she's layered, she's doing the most 🎀
  • settling_time_0 — literally not used. that's it, that's the whole member 😭
  • insn_bits_support — set to COMEDI_SUPPORTED if the subdevice supports the INSN_BITS instruction, or COMEDI_UNSUPPORTED if it does not. binary vibes only 💀
  • unused — reserved for future use. the placeholder bestie, holding space for tomorrow 🌸

💅 Description 💅

so here's the tea: this struct goes with the COMEDI_SUBDINFO ioctl, which copies an array of struct comedi_subdinfo back to user space, with one element per subdevice. to actually use this you need to know the number of subdevices, and you get that from the COMEDI_DEVINFO ioctl. no skipping steps, bestie 🤝

these are the subd_flags values that may be ORed together... 👇

  • SDF_BUSY — the subdevice is busy processing an asynchronous command or a synchronous instruction. she's occupied, do not disturb 🙈
  • SDF_BUSY_OWNER — the subdevice is busy processing an asynchronous acquisition command that was started on the current file object (the file object issuing the COMEDI_SUBDINFO ioctl). so it's your fault, but make it official 💅
  • SDF_LOCKED — the subdevice is locked by a COMEDI_LOCK ioctl. 🔒
  • SDF_LOCK_OWNER — the subdevice is locked by a COMEDI_LOCK ioctl from the current file object. you did the locking, congrats 👑
  • SDF_MAXDATA — maximum sample values are channel-specific. ✨
  • SDF_FLAGS — channel flags are channel-specific. 🎀
  • SDF_RANGETYPE — range types are channel-specific. 🌈
  • SDF_PWM_COUNTER — PWM can switch off automatically. ⚡
  • SDF_PWM_HBRIDGE — or PWM is signed (H-bridge). 🦋
  • SDF_CMD — the subdevice supports asynchronous commands. 🔥
  • SDF_SOFT_CALIBRATED — the subdevice uses software calibration. 🧚
  • SDF_CMD_WRITE — the subdevice supports asynchronous commands in the output ("write") direction. ✍️
  • SDF_CMD_READ — the subdevice supports asynchronous commands in the input ("read") direction. 📖
  • SDF_READABLE — the subdevice is readable (e.g. analog input). 👀
  • SDF_WRITABLE (aliased as SDF_WRITEABLE) — the subdevice is writable (e.g. analog output). yes bestie, there are two spellings, both valid, don't come for me 💖
  • SDF_INTERNAL — the subdevice has no externally visible lines. private account energy 🔐
  • SDF_GROUND — the subdevice can use ground as an analog reference. 🌍
  • SDF_COMMON — the subdevice can use a common analog reference. 🤝
  • SDF_DIFF — the subdevice can use differential inputs (or outputs). ➕➖
  • SDF_OTHER — the subdevice can use some other analog reference. the mystery option 💀
  • SDF_DITHER — the subdevice can do dithering. ✨
  • SDF_DEGLITCH — the subdevice can do deglitching. 🧼
  • SDF_MMAP — this is never set. ever. don't ask, it's just not happening 🙅‍♀️
  • SDF_RUNNING — an asynchronous command is still running. 🏃‍♀️
  • SDF_LSAMPL — the subdevice uses "long" (32-bit) samples (for asynchronous command data). 32-bit and thriving 💪
  • SDF_PACKED — the subdevice packs several DIO samples into a single sample (for asynchronous command data). compression queen 🎁
heads up bestie: no "channel flags" (flags) values are currently defined at all. empty list, zero entries, nothing to see 💀

🔥 SEE ALSO 🔥

Kernel file ./include/uapi/linux/comedi.h, plus these absolute icons:

  • enum comedi_subdevice_type(9)
  • enum comedi_io_direction(9)
  • enum configuration_ids(9)
  • enum comedi_digital_trig_op(9)
  • enum comedi_support_level(9)
  • enum comedi_counter_status_flags(9)
  • struct comedi_insn(9)
  • struct comedi_insnlist(9)
  • struct comedi_cmd(9)
  • struct comedi_chaninfo(9)
  • struct comedi_rangeinfo(9)
  • struct comedi_krange(9)
  • struct comedi_devinfo(9)
  • struct comedi_devconfig(9)
  • struct comedi_bufconfig(9)
  • struct comedi_bufinfo(9)

aaaand that's the page!! 🫶 this one came from the kernel file under ./include/uapi/linux, dated October 2026, and it's struct comedi_subdinfo(9) — go forth and read your subdevice info, bestie, you've got this 💖✨🎀

📦 where this page comes from