I have a P1015 based custom board which is to be booted using U-boot. I have worked out the u-boot part for the board, but require help in accessing a peripheral connected to the P1015 via a eLBC bus. The peripheral in question is a NVRAM (CY14B108L) - (8-Mbit - 1024 K × 8). We have planned to access this device via the GPCM mode of the eLBC bus, suggestions about the mode of access as to GPCM or UPM would be better (as we have not decided on which mode to use for access). Also how must one configure the registers of the eLBC for u-boot - (I am completely new to the eLBC based mode of accessing).I would also like to know how to go about using this peripheral in u-boot, whether there is any support for GPCM/UPM based accessing in u-boot for peripherals connected to eLBC bus in this mode. Could someone provide with some codes (links to codes - for using in u-boot)/similar examples for accessing a device similar to this (GPCM/UPM based eLBC connection). The NVRAM being used is not for booting but rather to read and write data.
P.S. - The eLBC is also used in GPCM mode by the NOR Flash which is the source of booting. Also I was informed that the general convention of use for the GPCM mode is for boot-loading (from NVRAM or NOR Flash) and access to low-performance memory-mapped peripherals.
I found out that the NOR Flash/bootloaders alone can be configured in the GPCM mode. Other peripherals used for read and write in the eLBC bus must come in the UPM configuration.
The configuration for the eLBC bus is defined in the fsl_lbc.h in the /arch/powerpc/include/
Also the initialization for the eLBC bus - i.e., the setting up of the eLBC bus is provided in the /arch/powerpc/cpu/mpc8xxx/fsl_lbc.c wherein the following line is present
#if defined(CONFIG_SYS_BRn_PRELIM) && defined(CONFIG_SYS_ORn_PRELIM)
This CONFIG_SYS_BRn_PRELIM and CONFIG_SYS_ORn_PRELIM must be defined in the board.h file
> Other peripherals used for read and write in the eLBC bus must come in the UPM configuration.
There is no absolute restriction.
The machine is chosen in accordance with the connected device datasheet.
I was wondering whether in addition to the NOR Flash (bootloader for my custom board), I could also use other peripherals in the GPCM mode i.e., to make my question clear can I have three devices connected to the eLBC bus in GPCM mode.
It could be advised to:
1) inspect current memory map
2) modify the memory map by adding the NVRAM memory area
3) inspect the U-Boot source code to understand which definitions are used for the NOR Flash
4) add definitions for the NVRAM