btashton opened a new pull request #1777:
URL: https://github.com/apache/incubator-nuttx/pull/1777
## Summary
The current EasyDMA implementation will fail if a transfer of over
255 bytes is requested with no warning.
Also we do not set the RX and TX transfer lengths to 0 if the
buffer is NULL which can cause data to be written to the old
address as well as cause unexpected transaction lengths.
### Example:
**transfer 1**:
```
rx_len = 10
rx_buff != NULL
tx_len = 10
tx_buff != NULL
```
**transfer 2**:
```
rx_len = 2
rx_buff != NULL
tx_buff == NULL
```
Total transaction length for the second would be 10 because it would still
be using the old tx length of 10 and would send the data in that buffer out.
## Impact
SPI transactions should be safer. And warnings are given when transactions
are too long.
## Testing
Driving a SPI display.
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