NAME

       lowlevel - Low level register access

SYNOPSIS

   Functions
       uint32_t * bcm2835_regbase (uint8_t regbase)
       uint32_t bcm2835_peri_read (volatile uint32_t *paddr)
       uint32_t bcm2835_peri_read_nb (volatile uint32_t *paddr)
       void bcm2835_peri_write (volatile uint32_t *paddr, uint32_t value)
       void bcm2835_peri_write_nb (volatile uint32_t *paddr, uint32_t value)
       void bcm2835_peri_set_bits (volatile uint32_t *paddr, uint32_t value, uint32_t mask)

Detailed Description

       These functions provide low level register access, and should not generally need to be
       used

Function Documentation

   uint32_t bcm2835_peri_read (volatile uint32_t * paddr)
       Reads 32 bit value from a peripheral address WITH a memory barrier before and after each
       read. This is safe, but slow. The MB before protects this read from any in-flight reads
       that didn't use a MB. The MB after protects subsequent reads from another peripheral.

       Parameters
           paddr Physical address to read from. See BCM2835_GPIO_BASE etc.

       Returns
           the value read from the 32 bit register

       See also
           Physical Addresses

   uint32_t bcm2835_peri_read_nb (volatile uint32_t * paddr)
       Reads 32 bit value from a peripheral address WITHOUT the read barriers You should only use
       this when: o your code has previously called bcm2835_peri_read() for a register within the
       same peripheral, and no read or write to another peripheral has occurred since. o your
       code has called bcm2835_memory_barrier() since the last access to ANOTHER peripheral.

       Parameters
           paddr Physical address to read from. See BCM2835_GPIO_BASE etc.

       Returns
           the value read from the 32 bit register

       See also
           Physical Addresses

   void bcm2835_peri_set_bits (volatile uint32_t * paddr, uint32_t value, uint32_t mask)
       Alters a number of bits in a 32 peripheral regsiter. It reads the current valu and then
       alters the bits defines as 1 in mask, according to the bit value in value. All other bits
       that are 0 in the mask are unaffected. Use this to alter a subset of the bits in a
       register. Memory barriers are used. Note that this is not atomic; an interrupt routine can
       cause unexpected results.

       Parameters
           paddr Physical address to read from. See BCM2835_GPIO_BASE etc.
           value The 32 bit value to write, masked in by mask.
           mask Bitmask that defines the bits that will be altered in the register.

       See also
           Physical Addresses

   void bcm2835_peri_write (volatile uint32_t * paddr, uint32_t value)
       Writes 32 bit value from a peripheral address WITH a memory barrier before and after each
       write This is safe, but slow. The MB before ensures that any in-flight write to another
       peripheral completes before this write is issued. The MB after ensures that subsequent
       reads and writes to another peripheral will see the effect of this write.

       This is a tricky optimization; if you aren't sure, use the barrier version.

       Parameters
           paddr Physical address to read from. See BCM2835_GPIO_BASE etc.
           value The 32 bit value to write

       See also
           Physical Addresses

   void bcm2835_peri_write_nb (volatile uint32_t * paddr, uint32_t value)
       Writes 32 bit value from a peripheral address without the write barrier You should only
       use this when: o your code has previously called bcm2835_peri_write() for a register
       within the same peripheral, and no other peripheral access has occurred since. o your code
       has called bcm2835_memory_barrier() since the last access to ANOTHER peripheral.

       This is a tricky optimization; if you aren't sure, use the barrier version.

       Parameters
           paddr Physical address to read from. See BCM2835_GPIO_BASE etc.
           value The 32 bit value to write

       See also
           Physical Addresses

   uint32_t* bcm2835_regbase (uint8_t regbase)
       Gets the base of a register

       Parameters
           regbase You can use one of the common values BCM2835_REGBASE_* in bcm2835RegisterBase

       Returns
           the register base

       See also
           Physical Addresses

Author

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