ar9003_hw_set_channel(9)

✨ ar9003_hw_set_channel(9) ✨

okay bestie, welcome to the Kernel API Manual — yes that's the manual name, and yes we're reading it together, grab a boba 🧋 because this one's about setting channels on a single-chip device and it's honestly kinda iconic 💅

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🎀 NAME 🎀

ar9003_hw_set_channel — set channel on single-chip device. that's it, that's the whole vibe, short and slay ✨

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🌸 SYNOPSIS 🌸

int ar9003_hw_set_channel (struct ath_hw *ah , struct ath9k_channel
*chan );

not me pasting this exactly as-is because we do not touch the signatures in this house 🫶

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🦋 ARGUMENTS 🦋

• ah — the atheros hardware structure, your main character struct fr fr 👑
• chan — literally just here existing 😭 the original gives it no description at all, so no cap, we're not inventing one. it's the struct ath9k_channel *, bestie, that's all we know from the signature 💀

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💖 DESCRIPTION 💖

so this is the function for changing the channel on single-chip devices — meaning the AR9300 family of chipsets, iykyk 🔥

it takes the channel value in MHz and sets the hardware channel value. oh and important caveat: it assumes writes have been enabled to the analog bus — like, that's a prerequisite, not a suggestion, so make sure that's already handled before you come calling 🙈

now the actual expressions, and these are giving math class but make it hardware 🧮✨

for a 2GHz channel, the channel frequency is:

Channel Frequency = (3/4) * freq_ref * (chansel[8:0] + chanfrac[16:0]/2^17)

with (freq_ref = 40MHz) ⭐

for a 5GHz channel, the channel frequency is:

Channel Frequency = (3/2) * freq_ref * (chansel[8:0] + chanfrac[16:0]/2^10)

with (freq_ref = 40MHz/(24>>amodeRefSel)) — yes that bit-shift is in there, it's not a typo, we keep it exactly as the page says 💜

and for 5GHz channels which are 5MHz spaced, the channel frequency is:

Channel Frequency = (3/2) * freq_ref * (chansel[8:0] + chanfrac[16:0]/2^17)

with (freq_ref = 40MHz) 🌈

heads up bestie, notice the 5MHz-spaced one uses /2^17 like the 2GHz formula, while the regular 5GHz one uses /2^10 — that's not me being chaotic, that's literally what the page says, so copy it carefully 👀

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🔍 SEE ALSO 🔍

• the kernel file ./drivers/net/wireless/ath/ath9k/ar9003_phy.c — go read the source, it ate 💅
• ar9003_hw_spur_mitigate_mrc_cck(9) — the friend of a friend, also important 🫶

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and that's the whole page, bestie 🎀💖 this gem comes from ./drivers/net/wireless/ath/ath9k, dated October 2026, and its title is of course ar9003_hw_set_channel(9) — slay, periodt, go set some channels responsibly ✨👑🌸