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update fifo per PanRe review

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hathach 2022-12-16 16:55:25 +07:00
parent 04a5c03ea8
commit 660343d200
2 changed files with 10 additions and 5 deletions
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8
src/common/tusb_fifo.c
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@ -352,9 +352,10 @@ static uint16_t backward_pointer(tu_fifo_t* f, uint16_t p, uint16_t offset)
return new_p; return new_p;
} }
// index to pointer, simply an modulo with minus // index to pointer, simply an modulo with minus.
static inline uint16_t idx2ptr(uint16_t idx, uint16_t depth) static inline uint16_t idx2ptr(uint16_t idx, uint16_t depth)
{ {
// Only run at most 3 times since index is limit in the range of [0..2*depth)
while ( idx >= depth ) idx -= depth; while ( idx >= depth ) idx -= depth;
return idx; return idx;
} }
@ -509,6 +510,7 @@ static uint16_t _tu_fifo_write_n(tu_fifo_t* f, const void * data, uint16_t n, tu
else if (overflowable_count + n >= 2*f->depth) else if (overflowable_count + n >= 2*f->depth)
{ {
// Double overflowed // Double overflowed
// Index is bigger than the allowed range [0,2*depth)
// re-position write index to have a full fifo after pushed // re-position write index to have a full fifo after pushed
wr_idx = advance_pointer(f, rd_idx, f->depth - n); wr_idx = advance_pointer(f, rd_idx, f->depth - n);
@ -518,7 +520,9 @@ static uint16_t _tu_fifo_write_n(tu_fifo_t* f, const void * data, uint16_t n, tu
// currently deliberately not implemented --> result in incorrect data read back // currently deliberately not implemented --> result in incorrect data read back
}else }else
{ {
// normal + single overflowed: just increase write index // normal + single overflowed:
// Index is in the range of [0,2*depth) and thus detect and recoverable. Recovering is handled in read()
// Therefore we just increase write index
// we will correct (re-position) read index later on in fifo_read() function // we will correct (re-position) read index later on in fifo_read() function
} }
} }

7
src/common/tusb_fifo.h
View File

@ -54,7 +54,7 @@ extern "C" {
/* Write/Read index is always in the range of: /* Write/Read index is always in the range of:
* 0 .. 2*depth-1 * 0 .. 2*depth-1
* The extra window allow us to determine the fifo state of empty or full with only 2 indexes * The extra window allow us to determine the fifo state of empty or full with only 2 indices
* Following are examples with depth = 3 * Following are examples with depth = 3
* *
* - empty: W = R * - empty: W = R
@ -86,7 +86,8 @@ extern "C" {
* ------------------------- * -------------------------
* | R | 1 | 2 | 3 | W | 5 | * | R | 1 | 2 | 3 | W | 5 |
* *
* - Double Overflowed: write(3), write(1), write(2) * - Double Overflowed i.e index is out of allowed range [0,2*depth) e.g:
* write(3), write(1), write(2)
* Continue to write after overflowed to 2nd overflowed. * Continue to write after overflowed to 2nd overflowed.
* We must prevent 2nd overflowed since it will cause incorrect computed of count, in above example * We must prevent 2nd overflowed since it will cause incorrect computed of count, in above example
* if not handled the fifo will be empty instead of continue-to-be full. Since we must not modify * if not handled the fifo will be empty instead of continue-to-be full. Since we must not modify
@ -94,7 +95,7 @@ extern "C" {
* after data is written it is a full fifo i.e W = depth - R * after data is written it is a full fifo i.e W = depth - R
* *
* re-position W = 1 before write(2) * re-position W = 1 before write(2)
* Note: we should also move data from mem[4] to read index as well, but deliberately skipped here * Note: we should also move data from mem[3] to read index as well, but deliberately skipped here
* since it is an expensive operation !!! * since it is an expensive operation !!!
* | * |
* ------------------------- * -------------------------