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Change maximum depth to 2^15 which allows for a fast modulo substitute.

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Thus, however, overflows are detectable only for one time FIFO depth.
This commit is contained in:
Reinhard Panhuber 2020-09-23 20:48:03 +02:00
parent 21299f90fa
commit 9bdeafb295
2 changed files with 37 additions and 40 deletions
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37
src/common/tusb_fifo.c
View File

@ -58,6 +58,8 @@ static void tu_fifo_unlock(tu_fifo_t *f)
bool tu_fifo_config(tu_fifo_t *f, void* buffer, uint16_t depth, uint16_t item_size, bool overwritable)
{
if (depth > 0x8000) return false; // Maximum depth is 2^15 items
tu_fifo_lock(f);
f->buffer = (uint8_t*) buffer;
@ -65,8 +67,8 @@ bool tu_fifo_config(tu_fifo_t *f, void* buffer, uint16_t depth, uint16_t item_si
f->item_size = item_size;
f->overwritable = overwritable;
f->non_used_index_space = 0x10000 % depth;
f->max_pointer_idx = 0xFFFF - f->non_used_index_space;
f->max_pointer_idx = 2*depth - 1; // Limit index space to 2*depth - this allows for a fast "modulo" calculation but limits the maximum depth to 2^16/2 = 2^15 and buffer overflows are detectable only if overflow happens once (important for unsupervised DMA applications)
f->non_used_index_space = 0xFFFF - f->max_pointer_idx;
f->rd_idx = f->wr_idx = 0;
@ -79,7 +81,9 @@ bool tu_fifo_config(tu_fifo_t *f, void* buffer, uint16_t depth, uint16_t item_si
static inline uint16_t _ff_mod(uint16_t idx, uint16_t depth)
{
return idx % depth;
// return idx % depth;
idx -= depth & -(idx > depth);
return idx -= depth & -(idx > depth);
}
// send one item to FIFO WITHOUT updating write pointer
@ -194,15 +198,11 @@ static inline bool _tu_fifo_full(tu_fifo_t* f, uint16_t wAbs, uint16_t rAbs)
}
// Works on local copies of w and r
//BE AWARE - THIS FUNCTION MIGHT NOT GIVE A CORRECT ANSWERE IN CASE WRITE POINTER "OVERFLOWS"
//EXAMPLE with buffer depth: 100
//Maximum index space: (2^16) - (2^16) % depth = 65500
//If you produce 65500 / 100 + 1 = 656 buffer overflows, the write pointer will overflow as well and
//the check _tu_fifo_overflow() will not give you a valid result! Avoid such nasty things!
//All reading functions (read, peek) check for overflows and correct read pointer on their own such
//that latest items are read.
//If required (e.g. for DMA use) you can also correct the read pointer by
//tu_fifo_correct_read_pointer().
// BE AWARE - THIS FUNCTION MIGHT NOT GIVE A CORRECT ANSWERE IN CASE WRITE POINTER "OVERFLOWS"
// Only one overflow is allowed for this function to work e.g. if depth = 100, you must not
// write more than 2*depth-1 items in one rush without updating write pointer. Otherwise
// write pointer wraps and you pointer states are messed up. This can only happen if you
// use DMAs, write functions do not allow such an error.
static inline bool _tu_fifo_overflow(tu_fifo_t* f, uint16_t wAbs, uint16_t rAbs)
{
return (_tu_fifo_count(f, wAbs, rAbs) > f->depth);
@ -249,6 +249,7 @@ static uint16_t _tu_fifo_peek_at_n(tu_fifo_t* f, uint16_t pos, void * p_buffer,
if (cnt > f->depth)
{
_tu_fifo_correct_read_pointer(f, wAbs);
rAbs = f->rd_idx;
cnt = f->depth;
}
@ -401,13 +402,11 @@ bool tu_fifo_read(tu_fifo_t* f, void * buffer)
{
tu_fifo_lock(f); // TODO: Here we may distinguish for read and write pointer mutexes!
uint16_t r = f->rd_idx;
// Peek the data
bool ret = _tu_fifo_peek_at(f, 0, buffer, f->wr_idx, r);
bool ret = _tu_fifo_peek_at(f, 0, buffer, f->wr_idx, f->rd_idx); // f->rd_idx might get modified in case of an overflow so we can not use a local variable
// Advance pointer
f->rd_idx = advance_pointer(f, r, ret);
f->rd_idx = advance_pointer(f, f->rd_idx, ret);
tu_fifo_unlock(f);
return ret;
@ -433,13 +432,11 @@ uint16_t tu_fifo_read_n(tu_fifo_t* f, void * buffer, uint16_t count)
{
tu_fifo_lock(f); // TODO: Here we may distinguish for read and write pointer mutexes!
uint16_t r = f->rd_idx;
// Peek the data
count = _tu_fifo_peek_at_n(f, 0, buffer, count, f->wr_idx, r);
count = _tu_fifo_peek_at_n(f, 0, buffer, count, f->wr_idx, f->rd_idx); // f->rd_idx might get modified in case of an overflow so we can not use a local variable
// Advance read pointer
f->rd_idx = advance_pointer(f, r, count);
f->rd_idx = advance_pointer(f, f->rd_idx, count);
tu_fifo_unlock(f);
return count;

40
src/common/tusb_fifo.h
View File

@ -48,7 +48,7 @@
#include <stdbool.h>
#ifdef __cplusplus
extern "C" {
extern "C" {
#endif
#if CFG_FIFO_MUTEX
@ -61,16 +61,16 @@
*/
typedef struct
{
uint8_t* buffer ; ///< buffer pointer
uint16_t depth ; ///< max items
uint16_t item_size ; ///< size of each item
bool overwritable ;
uint8_t* buffer ; ///< buffer pointer
uint16_t depth ; ///< max items
uint16_t item_size ; ///< size of each item
bool overwritable ;
uint16_t non_used_index_space ; ///< required for non-power-of-two buffer length
uint16_t max_pointer_idx ; ///< maximum absolute pointer index
uint16_t non_used_index_space ; ///< required for non-power-of-two buffer length
uint16_t max_pointer_idx ; ///< maximum absolute pointer index
volatile uint16_t wr_idx ; ///< write pointer
volatile uint16_t rd_idx ; ///< read pointer
volatile uint16_t wr_idx ; ///< write pointer
volatile uint16_t rd_idx ; ///< read pointer
#if CFG_FIFO_MUTEX
tu_fifo_mutex_t mutex;
@ -78,16 +78,16 @@ typedef struct
} tu_fifo_t;
#define TU_FIFO_DEF(_name, _depth, _type, _overwritable) \
uint8_t _name##_buf[_depth*sizeof(_type)]; \
tu_fifo_t _name = { \
.buffer = _name##_buf, \
.depth = _depth, \
.item_size = sizeof(_type), \
.overwritable = _overwritable, \
.non_used_index_space = 0x10000 % _depth, \
.max_pointer_idx = 0xFFFF - (0x10000 % _depth), \
}
#define TU_FIFO_DEF(_name, _depth, _type, _overwritable) \
uint8_t _name##_buf[_depth*sizeof(_type)]; \
tu_fifo_t _name = { \
.buffer = _name##_buf, \
.depth = _depth, \
.item_size = sizeof(_type), \
.overwritable = _overwritable, \
.max_pointer_idx = 2*_depth-1, \
.non_used_index_space = 0xFFFF - 2*_depth-1, \
}
bool tu_fifo_clear(tu_fifo_t *f);
bool tu_fifo_config(tu_fifo_t *f, void* buffer, uint16_t depth, uint16_t item_size, bool overwritable);
@ -131,7 +131,7 @@ static inline uint16_t tu_fifo_depth(tu_fifo_t* f)
}
#ifdef __cplusplus
}
}
#endif
#endif /* _TUSB_FIFO_H_ */