AM6442: About General-Purpose Memory Controller (GPMC)

Tomitama-san,

tomitama said:

1. Which of (A) and (B) is the correct memory map for GPMC?
  (A) 2.1 MAIN Domain Memory Map
    GPMC0_CFG 0x3B000000 to 0x3B0003FF
    GPMC0_DATA 0x50000000 to 0x57FFFFFF
  (B) 12.3.3.4.12 GPMC Memory Regions
    GPMC0_CFG 0x05390000 to 0x053903FF
    GPMC0_DATA 0x20000000 to 0x27FFFFFF

(A) is correct for AM64xx memory map
    CSL_GPMC0_CFG_BASE  0x3b000000
    CSL_GPMC0_CFG_SIZE  0x00000400
    CSL_GPMC0_DATA_BASE 0x50000000
    CSL_GPMC0_DATA_SIZE 0x08000000

(B) is correct for AM654x memory map

tomitama said:

2. Is the corresponding address (bit5-0: A29-A24) incorrect?
  The corresponding addresses are described as A29 to A24 in [bit5-0 BASE ADDRESS] of [13.3.3.6.17 GPMC_CONFIG7_i Register].
  For A29 to A24, the maximum address is 0x3F000000.
  In that case, GPMC0_DATA 0x50000000 to 0x57FFFFFF in Question 1- (B) cannot be specified.

The system address of 0x50000000 uses 32 bits.
The [bit5-0 BASE ADDRESS] field of GPMC_CONFIG7_i Register ignores bits 31 and 30 of the 32-bit address, and checks only bits [29-24]. Bits [5-0] corresponds to A29, A28, A27, A26, A25, and A24 of the 32-bit address.
For example, for base addres 0x50000000 bits[5-0] = 010000b.
31   30   29   28   27   26   25   24   23 ...
0    1    0    1    0    0    0    0    0  ...

The full GPMC range is accessible.

tomitama said:

3. Can I use 32bit data bus?
  There is no 32bit in [bit13-12 DEVICE SIZE] of [13.3.3.6.11 GPMC_CONFIG1_i Register].
    0h(R/W) = 8 bit
    1h(R/W) = 16 bit
    2h(R/W) = Reserved
    3h(R/W) = Reserved

Yes, 32-bit data bus can be used with async modes and sync modes upto 100MHz GPMC_CLK.

GPMC_CONFIG1_i Register [bits13-12 DEVICESIZE] = 2h(R/W) = 32 bit.
The value of 2h = 32 bit should not be Reserved.

I will file a bug against the TRM to remove the reserved and add a note to refer to the datasheet.

I will also file a bug against the datasheet to clarify that 16-bit supports 133MHz synch mode but 32-bit supports 100MHz synch mode.

It is advised to keep trace length to 4" to help to meet datasheet timings.

Regards,
Mark