8.7. Active Serial Configuration
The AS configuration scheme supports AS x1 (1-bit data width) and AS x4 (4-bit data width) modes. The AS x4 mode provides four times faster configuration time than the AS x1 mode. In the AS configuration scheme, the Stratix® V device controls the configuration interface.
In the AS configuration process, after power-up, the Stratix® V device drives the DCLK pin with the default 12.5 MHz internal oscillator to read the configuration bitstream from the serial flash. The device determines the configuration options such as clock source, DCLK frequency, ASx1, or ASx4 by reading the option bits, located from 0x80 to 0x127, at the start of the programming file stored in the serial flash.
After the option bit is decoded by the Stratix® V configuration control block, the AS configuration continues with the design option by reading the rest of the programming file from the serial flash until CONF_DONE pin asserts high and eventually enters user mode. When any interruption (such as data corruption) occurs in the middle of the AS Configuration, the nSTATUS pin will assert low to indicate configuration error, and deassert high to restart the configuration process. If there is no image in the serial flash or if the image is corrupted, you will observe the nSTATUS will pulse low repeatedly as the control block tries to configure itself forever, until the configuration is successful.
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