From 9bdeafb29503b65d2c46e71a4c7e80b753bad55a Mon Sep 17 00:00:00 2001
From: Reinhard Panhuber <panhuber_reinhard@gmx.at>
Date: Wed, 23 Sep 2020 20:48:03 +0200
Subject: [PATCH] Change maximum depth to 2^15 which allows for a fast modulo
substitute.
Thus, however, overflows are detectable only for one time FIFO depth.
---
src/common/tusb_fifo.c | 37 +++++++++++++++++--------------------
src/common/tusb_fifo.h | 40 ++++++++++++++++++++--------------------
2 files changed, 37 insertions(+), 40 deletions(-)
diff --git a/src/common/tusb_fifo.c b/src/common/tusb_fifo.c
index b83dfee4e..84fc9bb8b 100644
--- a/src/common/tusb_fifo.c
+++ b/src/common/tusb_fifo.c
@@ -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;
diff --git a/src/common/tusb_fifo.h b/src/common/tusb_fifo.h
index 66888ef19..23f5d8449 100644
--- a/src/common/tusb_fifo.h
+++ b/src/common/tusb_fifo.h
@@ -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_ */