bcm2835_rd_fifo_count(9)

💅 bcm2835_rd_fifo_count

ok so bestie, welcome to the Kernel API Manual — section 9, kernel-space girlies only, no cap. today's main character is bcm2835_rd_fifo_count, and she's giving "just grab the bytes and don't ask questions" energy. 🎀

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✨ NAME ✨

bcm2835_rd_fifo_count — blindly read exactly @count bytes from RX FIFO 🦋

like… blindly. she does not check. she does not verify. she trusts you. that's the vibe.

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🌸 SYNOPSIS 🌸

void bcm2835_rd_fifo_count (struct bcm2835_spi *bs , int count );

that's it. that's the whole function. two args, no return, no drama (well, the drama is on YOU, the caller — more on that in a sec 😭).

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🫶 ARGUMENTS 🫶

• bs — the BCM2835 SPI controller, aka the whole reason we're here 💖
• count — how many bytes to read from the RX FIFO, like literally the number of bytes, exactly that many, no more no less ✨

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👑 DESCRIPTION 👑

ok so before you even think about calling this, there is a whole checklist and the caller (that's you, bestie) is responsible for every single item on it. no cap. this function is not doing the vibes check for you:

• you MUST ensure that bs->rx_len is greater than or equal to count — like, greater than or equal, not "close enough" 🙈
• you MUST ensure the RX FIFO actually contains at least count bytes. yes, at least. if it doesn't, that's a you problem 💀
• you MUST ensure that the DMA Enable flag in the CS register is set, so that a read from the FIFO register receives 32-bit instead of just 8-bit 👑 (this one matters, it's the whole difference between the fancy wide read and the sad little 8-bit one)
• and, not to be that girl, but bs->rx_buf must not be NULL. like at all. ever. 🔥

so yeah, "blindly" in the NAME is doing a LOT of heavy lifting here. she reads exactly count bytes and trusts that the universe (you) set everything up perfectly. the setup is the whole assignment. 💅

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🌈 SEE ALSO 🌈

• Kernel file ./drivers/spi/spi-bcm2835.c 📁
• struct bcm2835_spi(9)
• struct bcm2835_spidev(9)
• bcm2835_wr_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)

the whole friend group fr fr, go say hi 🧚💜

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and that's the page, bestie!! 🍓 this lil gem lives over in ./drivers/spi, dated October 2026, and it's page bcm2835_rd_fifo_count(9) of the Kernel API Manual. mwah, go read your FIFO responsibly 💖✨💅