embox

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/**
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 * @file
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 * @brief Mailbox Communication mechanism for Raspberry Pi
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 *
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 * @date 16.07.15
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 * @author Michele Di Giorgio
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 */
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#include <errno.h>
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#include <stdint.h>
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#include <drivers/mailbox/bcm2835_mailbox.h>
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#include <hal/reg.h>
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#include <hal/mem_barriers.h>
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static struct bcm2835_mailbox_regs volatile *const mailbox_regs =
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        (struct bcm2835_mailbox_regs volatile *) BCM2835_MAILBOX_BASE;
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/**
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 * Read from memory mapped IO registers with a memory barrier around.
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 * @param addr - pointer to register address
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 *
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 * @return data read (returns a memory location)
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 */
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static uint32_t read_mmio(uint32_t volatile *addr) {
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    uint32_t n;
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    n = REG_LOAD(addr);
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    data_mem_barrier();
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    return n;
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}
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/**
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 * Write to memory mapped IO register with a memory barrier around.
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 * @param addr - pointer to register address
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 * @param val - data to be stored (a pointer to a memory location)
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 */
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static void write_mmio(uint32_t volatile *addr, uint32_t val) {
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    data_mem_barrier();
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    REG_STORE(addr, val);
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}
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int bcm2835_mailbox_write(uint32_t data, uint32_t channel) {
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    /* validate channel number */
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    if (channel > 15) {
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        return -EINVAL;
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    }
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    /* lowest 4 bits of data must be 0 and combine data and the channel */
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    uint32_t to_write = (data & BCM2835_MAILBOX_DATA_MASK) | channel;
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    /* read the status field and wait until ready */
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    while (read_mmio((uint32_t volatile *)&mailbox_regs->Status) & BCM2835_MAILBOX_FULL);
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    write_mmio((uint32_t volatile *)&mailbox_regs->Write, to_write);
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    return 0;
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}
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uint32_t bcm2835_mailbox_read(uint32_t channel) {
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    uint32_t data;
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    if (channel > 15) {
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        return -EINVAL;
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    }
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    /* repeat reading if the channel was wrong */
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    do {
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        while (read_mmio((uint32_t volatile *)&mailbox_regs->Status) & BCM2835_MAILBOX_EMPTY);
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        data = read_mmio((uint32_t volatile *)&mailbox_regs->Read);
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    } while ((data & BCM2835_MAILBOX_CHANNEL_MASK) != channel);
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    /* return the message only (top 28 bits of the read data) */
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    return data & BCM2835_MAILBOX_DATA_MASK;
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}
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