Download Play: Difference between revisions

(4 intermediate revisions by the same user not shown)

Line 66:

The checksum stored in the above data frame header is then calculated using this checksum seed.

First, the calc_checksum is initialized to 0. Then calc_checksum is added with ''all'' words in the data frame loaded as big-endian, with the data-frame checksum cleared to zero here. If the frame_size isn't word-aligned, the remaining <4-bytes are loaded as big-endian for adding as well.

Then this is run:

//During init before the above adding, shift and count are initialized:

//shift = (((u8*)&checksum_seed)[2] & 0xf) + 0x4;

//count = (((u8*)&checksum_seed)[3] & 0x7) + 0x2;

for(pos=0; pos<count; pos++)checksum = (checksum<<shift | checksum>>shift) ^ checksum_seed;//The u32 checksum_seed is byte-swapped on 3DS for this.

Lastly the calculated checksum is written to output as big-endian(hence on 3DS it's byte-swapped before writing to output).

==== Frames ====

Line 97:

Line 107:

|-

| 0x0

| ~~0x4~~

| 0x8

| ~~u32~~, ~~unknown~~.

| u64 DLP-child titleID. Must be a CTR TID-high, with the TID-high set for DLP-child. The low 4-bits of the TID-low must be clear.

|-

~~| 0x4~~

~~| u32, unknown~~.

|-

| 0x8

| 0x2

| u16, ~~unknown~~.

| u16, probably the DLP-child title-version.

|-

| 0xA

Line 118:

Line 124:

| 0xC

| 0x4

| u32, ~~unknown~~.

| u32, chunk_size. This is the chunk_size used for transferring the CIA. This is the exact size used for the FS .cia file-reads on the host, and the exact size used for [[Application_Manager_Services|AM]] CIA file-writes on the client(s). Normally this is 0x0003FFC0. This appears to be validated by the client at some point, using a large value for this triggers an "connection interrupted" error when trying to connect.

|-

| 0x10

@@ Line 66: / Line 66: @@
 The checksum stored in the above data frame header is then calculated using this checksum seed.
+First, the calc_checksum is initialized to 0. Then calc_checksum is added with ''all'' words in the data frame loaded as big-endian, with the data-frame checksum cleared to zero here. If the frame_size isn't word-aligned, the remaining <4-bytes are loaded as big-endian for adding as well.
+Then this is run:
+  //During init before the above adding, shift and count are initialized:
+  //shift = (((u8*)&checksum_seed)[2] & 0xf) + 0x4;
+  //count = (((u8*)&checksum_seed)[3] & 0x7) + 0x2;
+  for(pos=0; pos<count; pos++)checksum = (checksum<<shift | checksum>>shift) ^ checksum_seed;//The u32 checksum_seed is byte-swapped on 3DS for this.
+Lastly the calculated checksum is written to output as big-endian(hence on 3DS it's byte-swapped before writing to output).
 ==== Frames ====
@@ Line 97: / Line 107: @@
 |-
 | 0x0
-| 0x4
+| 0x8
-| u32, unknown.
+| u64 DLP-child titleID. Must be a CTR TID-high, with the TID-high set for DLP-child. The low 4-bits of the TID-low must be clear.
-|-
-| 0x4
-| 0x4
-| u32, unknown.
 |-
 | 0x8
 | 0x2
-| u16, unknown.
+| u16, probably the DLP-child title-version.
 |-
 | 0xA
@@ Line 118: / Line 124: @@
 | 0xC
 | 0x4
-| u32, unknown.
+| u32, chunk_size. This is the chunk_size used for transferring the CIA. This is the exact size used for the FS .cia file-reads on the host, and the exact size used for [[Application_Manager_Services|AM]] CIA file-writes on the client(s). Normally this is 0x0003FFC0. This appears to be validated by the client at some point, using a large value for this triggers an "connection interrupted" error when trying to connect.
 |-
 | 0x10