ascii2desc(9)

💅 ascii2desc — like, the ascii2desc(9) page, bestie ✨

okay so this is ascii2desc(9) from the Kernel API Manual, and honestly? it's a little helper that's carrying the whole USB descriptor operation on its back 🫶

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🌸 NAME 🌸

ascii2desc — the helper routine that's out here producing UTF-16LE string descriptors for you, no cap 💖

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✨ SYNOPSIS ✨

unsigned ascii2desc (char const *s , u8 *buf , unsigned len );

that's the whole vibe check — three args, one unsigned coming back at you 🌈

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🎀 ARGUMENTS 🎀

• s — a null-terminated ASCII string. and yeah, "ASCII" is doing a little bit of a stretch here, because it's actually ISO-8859-1 😭 character for character, that's what the page says.
• buf — the buffer where the USB string descriptor goes. it's giving header + UTF-16LE energy 💅
• len — the length, in bytes, of that descriptor buffer. and yes, it may be odd 🙈 they said it, not me.

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⭐ RETURN ⭐

it hands back the number of bytes it filled in, and the math is:

2 + 2*strlen(s)

...or len, whichever is less. that's it, that's the whole answer, periodt 👑

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💀 NOTE 💀

okay this part lowkey matters so pay attention bestie:

USB String descriptors can contain at most 126 characters. input strings longer than that get truncated. 😭 so don't come crying to me when your extra-long string gets chopped.

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🦋 SEE ALSO 🦋

the kernel file that's the main character here is ./drivers/usb/core/hcd.c, and then it's a whole friend group of references — every single one, iykyk:

• rh_string(9)
• usb_bus_init(9)
• usb_register_bus(9)
• usb_deregister_bus(9)
• register_root_hub(9)
• usb_calc_bus_time(9)
• usb_hcd_link_urb_to_ep(9)
• usb_hcd_check_unlink_urb(9)
• usb_hcd_unlink_urb_from_ep(9)
• usb_hcd_giveback_urb(9)
• usb_hcd_alloc_bandwidth(9)
• usb_hcd_reset_endpoint(9)
• usb_alloc_streams(9)
• usb_free_streams(9)
• usb_hcd_resume_root_hub(9)
• usb_bus_start_enum(9)
• usb_hcd_irq(9)
• usb_hc_died(9)
• usb_create_shared_hcd(9)
• usb_create_hcd(9)
• usb_stop_hcd(9)
• usb_add_hcd(9)
• usb_remove_hcd(9)

like, go read them, they're iconic too 💜

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anyway that's the page!! this one lives in ./drivers/usb/core, dated October 2026, and it's filed under ascii2desc(9) — mwah, go forth and convert your strings to UTF-16LE bestie 🧚‍♀️💖✨