hardware_divider

Low-level hardware-divider access. More...

Functions
static void	hw_divider_divmod_s32_start (int32_t a, int32_t b)
	Start a signed asynchronous divide. More...
static void	hw_divider_divmod_u32_start (uint32_t a, uint32_t b)
	Start an unsigned asynchronous divide. More...
static void	hw_divider_wait_ready (void)
	Wait for a divide to complete. More...
static divmod_result_t	hw_divider_result_nowait (void)
	Return result of HW divide, nowait. More...
static divmod_result_t	hw_divider_result_wait (void)
	Return result of last asynchronous HW divide. More...
static uint32_t	hw_divider_u32_quotient_wait (void)
	Return result of last asynchronous HW divide, unsigned quotient only. More...
static int32_t	hw_divider_s32_quotient_wait (void)
	Return result of last asynchronous HW divide, signed quotient only. More...
static uint32_t	hw_divider_u32_remainder_wait (void)
	Return result of last asynchronous HW divide, unsigned remainder only. More...
static int32_t	hw_divider_s32_remainder_wait (void)
	Return result of last asynchronous HW divide, signed remainder only. More...
divmod_result_t	hw_divider_divmod_s32 (int32_t a, int32_t b)
	Do a signed HW divide and wait for result. More...
divmod_result_t	hw_divider_divmod_u32 (uint32_t a, uint32_t b)
	Do an unsigned HW divide and wait for result. More...
static uint32_t	to_quotient_u32 (divmod_result_t r)
	Efficient extraction of unsigned quotient from 32p32 fixed point. More...
static int32_t	to_quotient_s32 (divmod_result_t r)
	Efficient extraction of signed quotient from 32p32 fixed point. More...
static uint32_t	to_remainder_u32 (divmod_result_t r)
	Efficient extraction of unsigned remainder from 32p32 fixed point. More...
static int32_t	to_remainder_s32 (divmod_result_t r)
	Efficient extraction of signed remainder from 32p32 fixed point. More...
static uint32_t	hw_divider_u32_quotient (uint32_t a, uint32_t b)
	Do an unsigned HW divide, wait for result, return quotient. More...
static uint32_t	hw_divider_u32_remainder (uint32_t a, uint32_t b)
	Do an unsigned HW divide, wait for result, return remainder. More...
static int32_t	hw_divider_quotient_s32 (int32_t a, int32_t b)
	Do a signed HW divide, wait for result, return quotient. More...
static int32_t	hw_divider_remainder_s32 (int32_t a, int32_t b)
	Do a signed HW divide, wait for result, return remainder. More...
static void	hw_divider_pause (void)
	Pause for exact amount of time needed for a asynchronous divide to complete.
static uint32_t	hw_divider_u32_quotient_inlined (uint32_t a, uint32_t b)
	Do a hardware unsigned HW divide, wait for result, return quotient. More...
static uint32_t	hw_divider_u32_remainder_inlined (uint32_t a, uint32_t b)
	Do a hardware unsigned HW divide, wait for result, return remainder. More...
static int32_t	hw_divider_s32_quotient_inlined (int32_t a, int32_t b)
	Do a hardware signed HW divide, wait for result, return quotient. More...
static int32_t	hw_divider_s32_remainder_inlined (int32_t a, int32_t b)
	Do a hardware signed HW divide, wait for result, return remainder. More...
void	hw_divider_save_state (hw_divider_state_t *dest)
	Save the calling cores hardware divider state. More...
void	hw_divider_restore_state (hw_divider_state_t *src)
	Load a saved hardware divider state into the current core's hardware divider. More...

Detailed Description

Low-level hardware-divider access.

The SIO contains an 8-cycle signed/unsigned divide/modulo circuit, per core. Calculation is started by writing a dividend and divisor to the two argument registers, DIVIDEND and DIVISOR. The divider calculates the quotient / and remainder % of this division over the next 8 cycles, and on the 9th cycle the results can be read from the two result registers DIV_QUOTIENT and DIV_REMAINDER. A 'ready' bit in register DIV_CSR can be polled to wait for the calculation to complete, or software can insert a fixed 8-cycle delay

This header provides low level macros and inline functions for accessing the hardware dividers directly, and perhaps most usefully performing asynchronous divides. These functions however do not follow the regular SDK conventions for saving/restoring the divider state, so are not generally safe to call from interrupt handlers

The pico_divider library provides a more user friendly set of APIs over the divider (and support for 64 bit divides), and of course by default regular C language integer divisions are redirected through that library, meaning you can just use C level / and % operators and gain the benefits of the fast hardware divider.

See also

pico_divider

Example

 
#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/divider.h"
 
int main() {
    stdio_init_all();
    printf("Hello, divider!\n");
 
    // This is the basic hardware divider function
    int32_t dividend = 123456;
    int32_t divisor = -321;
    divmod_result_t result = hw_divider_divmod_s32(dividend, divisor);
 
    printf("%d/%d = %d remainder %d\n", dividend, divisor, to_quotient_s32(result), to_remainder_s32(result));
 
    // Is it right?
 
    printf("Working backwards! Result %d should equal %d!\n\n",
           to_quotient_s32(result) * divisor + to_remainder_s32(result), dividend);
 
    // This is the recommended unsigned fast divider for general use.
    int32_t udividend = 123456;
    int32_t udivisor = 321;
    divmod_result_t uresult = hw_divider_divmod_u32(udividend, udivisor);
 
    printf("%d/%d = %d remainder %d\n", udividend, udivisor, to_quotient_u32(uresult), to_remainder_u32(uresult));
 
    // Is it right?
 
    printf("Working backwards! Result %d should equal %d!\n\n",
           to_quotient_u32(result) * divisor + to_remainder_u32(result), dividend);
 
    // You can also do divides asynchronously. Divides will be complete after 8 cycles.
 
    hw_divider_divmod_s32_start(dividend, divisor);
 
    // Do something for 8 cycles!
 
    // In this example, our results function will wait for completion.
    // Use hw_divider_result_nowait() if you don't want to wait, but are sure you have delayed at least 8 cycles
 
    result = hw_divider_result_wait();
 
    printf("Async result %d/%d = %d remainder %d\n", dividend, divisor, to_quotient_s32(result),
           to_remainder_s32(result));
 
    // For a really fast divide, you can use the inlined versions... the / involves a function call as / always does
    // when using the ARM AEABI, so if you really want the best performance use the inlined versions.
    // Note that the / operator function DOES use the hardware divider by default, although you can change
    // that behavior by calling pico_set_divider_implementation in the cmake build for your target.
    printf("%d / %d = (by operator %d) (inlined %d)\n", dividend, divisor,
           dividend / divisor, hw_divider_s32_quotient_inlined(dividend, divisor));
 
    // Note however you must manually save/restore the divider state if you call the inlined methods from within an IRQ
    // handler.
    hw_divider_state_t state;
    hw_divider_divmod_s32_start(dividend, divisor);
    hw_divider_save_state(&state);
 
    hw_divider_divmod_s32_start(123, 7);
    printf("inner %d / %d = %d\n", 123, 7, hw_divider_s32_quotient_wait());
 
    hw_divider_restore_state(&state);
    int32_t tmp = hw_divider_s32_quotient_wait();
    printf("outer divide %d / %d = %d\n", dividend, divisor, tmp);
    return 0;
}

Function Documentation

hw_divider_divmod_s32()

divmod_result_t hw_divider_divmod_s32	(	int32_t	a,
		int32_t	b
	)

Do a signed HW divide and wait for result.

Divide a by b, wait for calculation to complete, return result as a fixed point 32p32 value.

Parameters

a	The dividend
b	The divisor

Returns

Results of divide as a 32p32 fixed point value.

hw_divider_divmod_s32_start()

static void hw_divider_divmod_s32_start ( int32_t  a, int32_t  b  )

inlinestatic

Start a signed asynchronous divide.

Start a divide of the specified signed parameters. You should wait for 8 cycles (__div_pause()) or wait for the ready bit to be set (hw_divider_wait_ready()) prior to reading the results.

Parameters

a	The dividend
b	The divisor

hw_divider_divmod_u32()

divmod_result_t hw_divider_divmod_u32	(	uint32_t	a,
		uint32_t	b
	)

Do an unsigned HW divide and wait for result.

Divide a by b, wait for calculation to complete, return result as a fixed point 32p32 value.

Parameters

a	The dividend
b	The divisor

Returns

Results of divide as a 32p32 fixed point value.

hw_divider_divmod_u32_start()

static void hw_divider_divmod_u32_start ( uint32_t  a, uint32_t  b  )

inlinestatic

Start an unsigned asynchronous divide.

Start a divide of the specified unsigned parameters. You should wait for 8 cycles (__div_pause()) or wait for the ready bit to be set (hw_divider_wait_ready()) prior to reading the results.

Parameters

a	The dividend
b	The divisor

hw_divider_quotient_s32()

static int32_t hw_divider_quotient_s32 ( int32_t  a, int32_t  b  )

inlinestatic

Do a signed HW divide, wait for result, return quotient.

Divide a by b, wait for calculation to complete, return quotient.

Parameters

a	The dividend
b	The divisor

Returns

Quotient results of the divide

hw_divider_remainder_s32()

static int32_t hw_divider_remainder_s32 ( int32_t  a, int32_t  b  )

inlinestatic

Do a signed HW divide, wait for result, return remainder.

Divide a by b, wait for calculation to complete, return remainder.

Parameters

a	The dividend
b	The divisor

Returns

Remainder results of the divide

hw_divider_restore_state()

void hw_divider_restore_state

(

hw_divider_state_t *

src

)

Load a saved hardware divider state into the current core's hardware divider.

Copy the passed hardware divider state into the hardware divider.

Parameters

src	the location to load the divider state from

hw_divider_result_nowait()

static divmod_result_t hw_divider_result_nowait ( void  )

inlinestatic

Return result of HW divide, nowait.

Note

This is UNSAFE in that the calculation may not have been completed.

Returns

Current result. Most significant 32 bits are the remainder, lower 32 bits are the quotient.

hw_divider_result_wait()

static divmod_result_t hw_divider_result_wait ( void  )

inlinestatic

Return result of last asynchronous HW divide.

This function waits for the result to be ready by calling hw_divider_wait_ready().

Returns

Current result. Most significant 32 bits are the remainder, lower 32 bits are the quotient.

hw_divider_s32_quotient_inlined()

static int32_t hw_divider_s32_quotient_inlined ( int32_t  a, int32_t  b  )

inlinestatic

Do a hardware signed HW divide, wait for result, return quotient.

Divide a by b, wait for calculation to complete, return quotient.

Parameters

a	The dividend
b	The divisor

Returns

Quotient result of the divide

hw_divider_s32_quotient_wait()

static int32_t hw_divider_s32_quotient_wait ( void  )

inlinestatic

Return result of last asynchronous HW divide, signed quotient only.

This function waits for the result to be ready by calling hw_divider_wait_ready().

Returns

Current signed quotient result.

hw_divider_s32_remainder_inlined()

static int32_t hw_divider_s32_remainder_inlined ( int32_t  a, int32_t  b  )

inlinestatic

Do a hardware signed HW divide, wait for result, return remainder.

Divide a by b, wait for calculation to complete, return remainder.

Parameters

a	The dividend
b	The divisor

Returns

Remainder result of the divide

hw_divider_s32_remainder_wait()

static int32_t hw_divider_s32_remainder_wait ( void  )

inlinestatic

Return result of last asynchronous HW divide, signed remainder only.

This function waits for the result to be ready by calling hw_divider_wait_ready().

Returns

Current remainder results.

hw_divider_save_state()

void hw_divider_save_state

(

hw_divider_state_t *

dest

)

Save the calling cores hardware divider state.

Copy the current core's hardware divider state into the provided structure. This method waits for the divider results to be stable, then copies them to memory. They can be restored via hw_divider_restore_state()

Parameters

dest	the location to store the divider state

hw_divider_u32_quotient()

static uint32_t hw_divider_u32_quotient ( uint32_t  a, uint32_t  b  )

inlinestatic

Do an unsigned HW divide, wait for result, return quotient.

Divide a by b, wait for calculation to complete, return quotient.

Parameters

a	The dividend
b	The divisor

Returns

Quotient results of the divide

hw_divider_u32_quotient_inlined()

static uint32_t hw_divider_u32_quotient_inlined ( uint32_t  a, uint32_t  b  )

inlinestatic

Do a hardware unsigned HW divide, wait for result, return quotient.

Divide a by b, wait for calculation to complete, return quotient.

Parameters

a	The dividend
b	The divisor

Returns

Quotient result of the divide

hw_divider_u32_quotient_wait()

static uint32_t hw_divider_u32_quotient_wait ( void  )

inlinestatic

Return result of last asynchronous HW divide, unsigned quotient only.

This function waits for the result to be ready by calling hw_divider_wait_ready().

Returns

Current unsigned quotient result.

hw_divider_u32_remainder()

static uint32_t hw_divider_u32_remainder ( uint32_t  a, uint32_t  b  )

inlinestatic

Do an unsigned HW divide, wait for result, return remainder.

Divide a by b, wait for calculation to complete, return remainder.

Parameters

a	The dividend
b	The divisor

Returns

Remainder results of the divide

hw_divider_u32_remainder_inlined()

static uint32_t hw_divider_u32_remainder_inlined ( uint32_t  a, uint32_t  b  )

inlinestatic

Do a hardware unsigned HW divide, wait for result, return remainder.

Divide a by b, wait for calculation to complete, return remainder.

Parameters

a	The dividend
b	The divisor

Returns

Remainder result of the divide

hw_divider_u32_remainder_wait()

static uint32_t hw_divider_u32_remainder_wait ( void  )

inlinestatic

Return result of last asynchronous HW divide, unsigned remainder only.

This function waits for the result to be ready by calling hw_divider_wait_ready().

Returns

Current unsigned remainder result.

hw_divider_wait_ready()

static void hw_divider_wait_ready ( void  )

inlinestatic

Wait for a divide to complete.

Wait for a divide to complete

to_quotient_s32()

static int32_t to_quotient_s32 ( divmod_result_t  r )

inlinestatic

Efficient extraction of signed quotient from 32p32 fixed point.

Parameters

r	32p32 fixed point value.

Returns

Unsigned quotient

to_quotient_u32()

static uint32_t to_quotient_u32 ( divmod_result_t  r )

inlinestatic

Efficient extraction of unsigned quotient from 32p32 fixed point.

Parameters

r	32p32 fixed point value.

Returns

Unsigned quotient

to_remainder_s32()

static int32_t to_remainder_s32 ( divmod_result_t  r )

inlinestatic

Efficient extraction of signed remainder from 32p32 fixed point.

Parameters

r	32p32 fixed point value.

Returns

Signed remainder

Note

On arm this is just a 32 bit register move or a nop

to_remainder_u32()

static uint32_t to_remainder_u32 ( divmod_result_t  r )

inlinestatic

Efficient extraction of unsigned remainder from 32p32 fixed point.

Parameters

r	32p32 fixed point value.

Returns

Unsigned remainder

Note

On Arm this is just a 32 bit register move or a nop