kingkevin
/
stm8s
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

main: calculate EDID length of multiple extensions

This commit is contained in:
King Kévin 2022-08-05 12:44:52 +02:00
parent 298f0ea3ca
commit f486521126
1 changed files with 17 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
main.c
View File

@ -105,18 +105,16 @@ static bool checksum_ok(const uint8_t* data, uint16_t length)
return (0 == checksum);
}
// return if the current EDID is valid
// return if the current EDID its length (including extensions), or 0 if invalid
/* from HDMI 1.3a specification
* All Sinks shall contain an CEA-861-D compliant E-EDID data structure.
* A Source shall read the EDID 1.3 and first CEA Extension to determine the capabilities supported
by the Sink.
* The first 128 bytes of the E-EDID shall contain an EDID 1.3 structure. The contents of this
structure shall also meet the requirements of CEA-861-D.
* A Source shall read the EDID 1.3 and first CEA Extension to determine the capabilities supported by the Sink.
* The first 128 bytes of the E-EDID shall contain an EDID 1.3 structure. The contents of this structure shall also meet the requirements of CEA-861-D.
*
* HDMI 2.1 uses CTA-861-G
* this uses EDID 1.4 structure
* EDID 1.3/1.4 is 128 bytes long, and can point to 128 bytes extension
* EDID 2.0 with its 256 bytes does not seem to be used in HDMI at all
* EDID 2.0 with its 256 bytes does not seem to be used in HDMI at all (and is deprecated, replaced by E-EDID)
* DisplayID with its variable-length structure meant to replace E-EDID only seems to be used in DisplayPort
*/
static uint16_t edid_length(const uint8_t* edid)
@ -129,28 +127,28 @@ static uint16_t edid_length(const uint8_t* edid)
}
if (1 == edid[18]) { // EDID 1.3/1.4 128-byte structure
if (checksum_ok(&edid[0], 128)) {
if (0 == edid[126]) { // no extension
puts("128 bytes\r\n");
return 128;
} else { // extension available
// the usual extension is CEA EDID Timing Extension (with extension tag 02), but we allow others
// no idea how more than 1 extension is supported
if (checksum_ok(&edid[128], 128)) {
puts("256 bytes (with extension)\r\n");
return 256;
} else {
if (checksum_ok(&edid[0], 128)) { // ensure checksum of base EDID is ok
const uint16_t length = 128 + (1 + edid[126]) * 128; // get length with all extensions
puts("(v1.4 ");
putn(edid[126] / 100);
putn((edid[126] / 10) % 10);
putn(edid[126] % 10);
puts(" extension) ");
for (uint16_t i = 128; i < length && i < 256; i += 128) { // verify checksum of each extension (we actually only support one extension)
if (!checksum_ok(&edid[i], 128)) {
puts("extension CRC error\r\n");
return 0; // EDID is broken
}
}
puts("CRC ok\r\n");
return length;
} else {
puts("CRC error\r\n");
puts("base CRC error\r\n");
return 0;
}
} else if (2 == edid[18]) { // EDID 2.0 256-byte structure
if (checksum_ok(&edid[0], 256)) {
puts("256 bytes (no extension)\r\n");
puts("(v2) CRC ok\r\n");
return 256;
} else {
puts("CRC error\r\n");