The document discusses physical to DRAM address mapping. It shows the default mapping which creates unused memory holes for video data. An alternative mapping is proposed to reclaim these holes by using a continuous linear address space. This requires configuring the MIPS MMU to allow virtual addresses to access the alternative physical mapping rather than only the default.

1. Physical Address to DRAM Address
Mapping
2048 (16 pages)
64 KB aligned 1920 (15 pages)
Bank 4m Bank 4m+1 (m = 0 or 1) Bank 4m+2 Bank 4m+3 Unused Portion
1/16 for 1920*1080
System Adr System Adr System Adr System Adr
(decimal) (decimal) (decimal) (decimal) 6/16 for 1280*720
Row Adr n
0~127 128~256 1792~1919 1920~2047 19/64 for 720*480
2048~2175 2176~2303 3840~3967 3968~4095
| | | |
| | No bank | | Dual 2KB page size
63488~63615 63616~63743 conflict 65280~65407 65408~65535 DRAM (4KB total)
Line 0~31 case for
Bank 4m + 2 Bank 4m + 3 rectangular Bank 4m Bank 4m + 1 CA[4:0] = HA[6:2]
DRAM CA[9:5] = HA[15:11]
System Adr System Adr System Adr System Adr
(hex) (hex)
access (hex) (hex)
BA[0] = HA[7]
10000~1007f 10080~100ff 10700~1077f 10780~107ff BA[1] = HA[8]^HA[16]
Row Adr n+4 10800~1087f 10880~108ff 10f00~10f7f 10f80~10fff RA[1:0] = HA[10:9]
| | | | RA[12:2] =HA[26 :16]
| | | |
Line 32~63 1f800~1f87f 1f880~1f8ff 1ff00~1ff7f 1ff80~1ffff

2. Memory Holes for Video (Boda7503) Data
1920*1080
1280*720 640*480
0000000
Video Data Video Data
1000000
2000000
Memory hole with
3000000
discontinuous address
4000000
5000000
6000000
7000000

3. Pros/Cons for the Address Mapping
 Advantage
 Simple DRAM memory address mapping
 All engines and processors see straight forward linear
address layout
 Disadvantage
 Create unused scattered holes in system memory for
video (Boda7503 generated) data
 The unused holes are difficult for software to utilize

4. Alternative Mapping to Reclaim Memory Holes
2048 (16 pages)
64 KB aligned 1920 (15 pages)
Bank 4m Bank 4m+1 (m = 0 or 1) Bank 4m+2 Bank 4m+3 Continuous
address
System Adr System Adr System Adr
System Adr
Row Adr n (hex)
(hex) (hex) (hex)
100000~ e00000~ f00000~
0~fff
100fff e00fff f00fff
Dual 2KB page size
DRAM (4KB total)
Bank 4m + 2 Bank 4m + 3 Bank 4m Bank 4m + 1 CA[9:0] = HA[11:2]
BA[0] = HA[20]
System Adr
BA[1] =
System Adr
System Adr
(hex)
System Adr HA[21]^HA[12]
Row Adr n+4 (hex)
(hex)
e01000~
(hex) RA[1:0] = HA[23:22]
101000~ f01000~
1000~1fff
101fff
e01fff
f01fff RA[9:2] =HA[19:12]
RA[12:10] = HA[26:24]
System Adr
(hex)
fff000~
ffffff

5. Alternative Mapping to Reclaim Memory Holes
Default Address Space Address Space of Extra Mapping
00000000 80000000
01000000 Same Video Data 81000000
With different address
02000000 82000000
03000000 83000000
04000000 84000000
05000000 Memory hole with 85000000
discontinuous address
06000000 86000000
07000000 Memory hole with 87000000
continuous address

6. MIPS Virtual to Physical Address Mapping
Virtual Address Physical Address
FFFFFFFF FFFFFFFF Same Repetitive
Kernal Mapped kseg3 DRAM Mapping
E0000000 (A[30:29] ignored)
DFFFFFFF
Supervisor Mapped kseg2
C0000000 Alternative DRAM
BFFFFFFF Kernal Unmapped Mapping
kseg1
Uncached Same Repetitive
A0000000 DRAM Mapping
9FFFFFFF
Kernal Unmapped kseg0 (A[30:29] ignored)
80000000
80000000
7FFFFFFF
7FFFFFFF
Default DRAM
User Mapped useg/kuseg Mapping
The upper 96MB
DRAM space
20000000
SPI_Flash/Device 1A000000 overlapped with
96MB
512MB SPI/Device can be
accessed here
00000000 00000000

7. MIPS Virtual to Physical Address Mapping
 Kseg1/kseg0 cannot access alternate DRAM mapping
region
 For 512MB DRAM, 96MB is wasted if software use only
kseg1/kseg0
 Software must configure MMU for kseg3/kseg2/useg to
access alternative DRAM mapping space or the 96MB
DRAM space that conflicts with SPI_Flash/Device space
on kseg1/kseg0.