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stmfx07: usb: keep better track of rxbcnt 

When reading a portion of the packet that is not divisible by 4 and
not equal to rxbcnt the count could get off, since 4 bytes are read
from the fifo in the last step but rxbcnt was only updated by the
number of bytes the caller requested.

We fix this by always subtracting four bytes (the number of bytes
read from the fifo) when we read a word from the fifo.  Care has
to be taken in the last step so that rxbcnt doesn't underflow (it
is an unsigned number).

Note that reading in several small chunks not divisible by 4 doesn't
work as the extra bytes read in the last step are always discarded.
This commit is contained in:
Jochen Hoenicke 2016-07-10 14:15:00 +02:00 committed by Karl Palsson
parent a4f1568b7d
commit 94f92d54d6
1 changed files with 8 additions and 1 deletions
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9
lib/usb/usb_fx07_common.c
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@ -228,15 +228,22 @@ uint16_t stm32fx07_ep_read_packet(usbd_device *usbd_dev, uint8_t addr,
uint32_t extra;
len = MIN(len, usbd_dev->rxbcnt);
usbd_dev->rxbcnt -= len;
volatile uint32_t *fifo = REBASE_FIFO(addr);
for (i = len; i >= 4; i -= 4) {
*buf32++ = *fifo++;
usbd_dev->rxbcnt -= 4;
}
if (i) {
extra = *fifo++;
/* we read 4 bytes from the fifo, so update rxbcnt */
if (usbd_dev->rxbcnt < 4) {
/* Be careful not to underflow (rxbcnt is unsigned) */
usbd_dev->rxbcnt = 0;
} else {
usbd_dev->rxbcnt -= 4;
}
memcpy(buf32, &extra, i);
}