Accessing memory loaded via tftp

I am trying to access data from a file that I load in via tftp. I'm using an AM3358 processor

tftp 81000000 mydata

and I can see the data being correctly loaded

=> md 81000000
81000000: 00004000 00000000 00002000 00000400    .@....... ......

In the u-boot code, I create a pointer to this address and then attempt to de-reference it, but the value is incorrect which makes me think I'm using the incorrect address

unsigned long addr = 0x81000000;
uint32_t *ptr = &addr;
uint32_t val = *(ptr+0);
printf("addr %ul val: %ul", addr, val);

Furthermore, I'm trying to load the address of mydata into a 32-bit LCD register, but the physical address of 0x81000000 is beyond that of a 32-bit number. I believe I'm just confused as to what address mapping is involved here.

bdi yields

=> bdi
arch_number = 0x00000000
boot_params = 0x80000100
DRAM bank   = 0x00000000
-> start    = 0x80000000
-> size     = 0x20000000
baudrate    = 115200 bps
TLB addr    = 0x9fff0000
relocaddr   = 0x9ffb4000
reloc off   = 0x1f7b4000
irq_sp      = 0x9df8ba90
sp start    = 0x9df8ba80
Early malloc usage: 4a8 / 1000
fdt_blob    = 0x9df8bea0

Why would 0x81000000 not be a valid 32 bit number ?

0x00000000 <= 0x81000000 <= 0xFFFFFFFF.

I think there may be an error in your logic: you are initializing ptrwith the address of addr, not the address of its content.

The correct code would rather be something like:

uint32_t addr = 0x81000000;
uint32_t *ptr = (uint32_t*)(uintptr_t) addr;
uint32_t val = *(ptr+0);
printf("addr %ul val: %ul", addr, val);

This can be tested on your PC - you may need to add support for building 32 bit applications, i.e. execute sudo apt-get install gcc-multilib on Ubuntu.

ptr.c:

#include <stdio.h>
#include <stdint.h>

int
main ()
{
  uint32_t addr = 0x81000000; // gcc 9.3.0 is complaining about uint32_t *ptr = &addr;
  
  // your code
  {
    uint32_t *ptr = &addr;
    printf ("%p\n", ptr);
  }

  // correct code
  {
    uint32_t *ptr = (uint32_t *) (uintptr_t) addr;
    printf ("%p\n", ptr);
  }
}

gcc -m32 -o ptr ptr.c

./ptr
0xff83bc60
0x81000000

This would be why you cannot access the content of the file you transferred using TFTP, you are reading from an incorrect, but valid address.