bcm2835_wr_fifo_count(9)

💅 bcm2835_wr_fifo_count — like, the Kernel API Manual one

okay so bestie, buckle up, because this is a kernel function page and it's from the Kernel API Manual and the vibe is very much "trust me, I know what I'm doing" 🫶

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✨ NAME ✨

bcm2835_wr_fifo_count — blindly write exactly count bytes to TX FIFO 💌

ngl the word "blindly" is doing so much heavy lifting here and we should all respect it 😭

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🌸 SYNOPSIS 🌸

void bcm2835_wr_fifo_count (struct bcm2835_spi *bs , int count );

like, that's it. that's the whole function signature. no return value, it's giving "i do this and i leave" energy 👑

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🎀 ARGUMENTS 🎀

• bs — the BCM2835 SPI controller. your main character, fr fr 💜
• count — the bytes to write to TX FIFO. exactly how many, no more no less, periodt ✨

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🦋 DESCRIPTION 🦋

so here's the thing, and listen closely because this is the whole plot: the caller must ensure a few things before calling this. and by "the caller must ensure" i mean you, bestie. it's a whole vibe check and you have to pass it 💅

• bs->tx_len has to be greater than or equal to count — no overachieving, okay?
• the TX FIFO has to be able to accommodate count bytes — like, there has to be room at the inn 🏨
• the DMA Enable flag in the CS register has to be set, such that a write to the FIFO register transmits 32-bit instead of just 8-bit. lowkey crucial, don't skip it or it's giving chaos 😭

no cap, this function does not check any of that for you. it "blindly" writes, which is literally in the NAME. the guardrails are your problem, not hers 🙈

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⭐ SEE ALSO ⭐

• the kernel file ./drivers/spi/spi-bcm2835.c — the mothership 🛸
• struct bcm2835_spi(9)
• struct bcm2835_spidev(9)
• bcm2835_rd_fifo_count(9)
• bcm2835_wait_tx_fifo_empty(9)
• bcm2835_rd_fifo_blind(9)
• bcm2835_wr_fifo_blind(9)
• bcm2835_spi_transfer_prologue(9)
• bcm2835_spi_undo_prologue(9)
• bcm2835_spi_dma_rx_done(9)
• bcm2835_spi_dma_tx_done(9)
• bcm2835_spi_prepare_sg(9)
• bcm2835_spi_transfer_one_dma(9)

it's a whole friend group honestly, they all show up together 🧚🌈

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and that's the page bestie!! this one lives in ./drivers/spi and it's dated October 2026 💖 go forth, write your bytes, and remember the DMA Enable flag 🌸✨