mirror of
https://github.com/isometimes/rpi4-osdev
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40 lines
1.2 KiB
C
40 lines
1.2 KiB
C
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#include "io.h"
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// The buffer must be 16-byte aligned as only the upper 28 bits of the address can be passed via the mailbox
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volatile unsigned int __attribute__((aligned(16))) mbox[36];
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enum {
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VIDEOCORE_MBOX = (PERIPHERAL_BASE + 0x0000B880),
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MBOX_READ = (VIDEOCORE_MBOX + 0x0),
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MBOX_POLL = (VIDEOCORE_MBOX + 0x10),
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MBOX_SENDER = (VIDEOCORE_MBOX + 0x14),
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MBOX_STATUS = (VIDEOCORE_MBOX + 0x18),
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MBOX_CONFIG = (VIDEOCORE_MBOX + 0x1C),
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MBOX_WRITE = (VIDEOCORE_MBOX + 0x20),
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MBOX_RESPONSE = 0x80000000,
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MBOX_FULL = 0x80000000,
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MBOX_EMPTY = 0x40000000
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};
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unsigned int mbox_call(unsigned char ch)
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{
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// 28-bit address (MSB) and 4-bit value (LSB)
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unsigned int r = ((unsigned int)((long) &mbox) &~ 0xF) | (ch & 0xF);
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// Wait until we can write
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while (mmio_read(MBOX_STATUS) & MBOX_FULL);
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// Write the address of our buffer to the mailbox with the channel appended
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mmio_write(MBOX_WRITE, r);
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while (1) {
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// Is there a reply?
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while (mmio_read(MBOX_STATUS) & MBOX_EMPTY);
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// Is it a reply to our message?
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if (r == mmio_read(MBOX_READ)) return mbox[1]==MBOX_RESPONSE; // Is it successful?
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}
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return 0;
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}
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