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icE1usb fw: Fix computation of received E1 frames from USB 

Several issues :

 - The reported length includes the CRC so it's minus 6 and
   not minus 4. (2 for CRC, 4 for header)

 - Cast length to int to make it signed so the minus works

 - If the packet is empty, this would be negative (no header),
   underflow, and then try to submit a giant number of frames
   to the E1 hardware

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Change-Id: Ib754e460290fe2e1551a0090e30a51846131d07d
This commit is contained in:
Sylvain Munaut 2022-01-03 21:11:05 +01:00
parent ff44f147f6
commit d108dfb9af
1 changed files with 3 additions and 2 deletions
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5
firmware/ice40-riscv/icE1usb/usb_e1.c
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@ -171,8 +171,9 @@ usb_e1_run(void)
usb_data_read(&hdr, ptr, 4);
/* Empty data into the FIFO */
int n = ((csr & USB_BD_LEN_MSK) - 4) / 32;
n = e1_tx_feed_data((ptr >> 2) + 1, n);
int n = ((int)(csr & USB_BD_LEN_MSK) - 6) / 32;
if (n > 0)
e1_tx_feed_data((ptr >> 2) + 1, n);
refill:
/* Refill it */