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Update README.md

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Clifford Wolf 2017-09-21 18:53:54 +02:00 committed by GitHub
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@ -76,3 +76,14 @@ The following settings for CRM/DDR/QSPI modes are valid:
| 0 | 1 | 1 | EDh DDR Quad I/O Read | FFh | | 0 | 1 | 1 | EDh DDR Quad I/O Read | FFh |
| 1 | 1 | 1 | EDh DDR Quad I/O Read | A5h | | 1 | 1 | 1 | EDh DDR Quad I/O Read | A5h |
The following plot visualizes the relative performance of the different configurations:
![](performance.png)
Consult the datasheet for your SPI flash to learn which configurations are supported
by the chip and what the maximum clock frequencies are for each configuration.
For Quad I/O mode the QUAD flag in CR1V must be set before enabling Quad I/O in the
SPI master. Either set it by writing the corresponding bit in CR1NV once, or by writing
it from your device firmware at every bootup. (See `set_flash_qspi_flag()` in
`firmware.c` for an example for the latter.)