SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
To ensure a correct, fast external boot (see Fast External Booting, in Initialization) with a GPMC access on device reset, several pins are sampled:
If WAIT pin monitoring function is enabled upon booting (i.e. BOOT_WAIT_EN="1"), the default (power-on-reset) monitored input for CS0 is always the device gpmc_wait0 input.
Signal Name | Width | Description |
---|---|---|
BOOT_DEVICE_SIZE | 1 | Size of the device attached on CS0 0b00: 8-bit 0b01: 16-bit 0b10: Reserved (not used) 0b11: Reserved (not used) |
CS0_MUX_DEVICE | 2 | Multiplexing mode of the device on CS0 0b00: Nonmultiplexed device on CS0 0b01: AAD-multiplexed device on CS0 (address-address-data) 0b10: Address/data-multiplexed device on CS0 0b11: Reserved |
BOOT_WAIT_EN | 1 | Wait monitoring on CS0 at device reset release time for read accesses 0: Wait pin is not monitored 1: Wait pin is monitored |
Using the internal boot code, the entire CS0 configuration can be modified before the first CS0 access. For more information, see Memory Booting, and Image Format, in Initialization. This modification of internal boot code is necessary for two external devices:
At reset time, the device can boot from the internal ROM.
The reset values of the timing control parameters are defined to cope with direct boot on address and data-multiplexed NOR flash devices, nonmultiplexed NOR flash devices, or any asynchronous device with large timing margins, assuming a low GPMC_FCLK frequency (for example, 19.2 MHz) at boot time.
For a multiplexed access, the address 16 low-order bits are presented onto gpmc_ad[15:0], while the high-order bits are presented onto gpmc_a[26:16]. If the external chip interface to the memories uses a 16-bit data bus, the high-order address bits are sampled on the address bus.
The reset values of timing parameters used at boot time are:
For an AAD-multiplexed access, all address bits are passed onto the data bus using two nADV rising edges. The first rising edge latches the address most-significant bit (MSB) down to bit 17, while the second rising edge latches address bits 16 down to 1. This configuration is only used for 16-bit memories.
The reset values of these timing parameters used at boot time are: