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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
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36
main.c
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@ -105,18 +105,16 @@ static bool checksum_ok(const uint8_t* data, uint16_t length)
return (0 == checksum); 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 /* from HDMI 1.3a specification
* All Sinks shall contain an CEA-861-D compliant E-EDID data structure. * 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 * A Source shall read the EDID 1.3 and first CEA Extension to determine the capabilities supported by the Sink.
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.
* 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 * HDMI 2.1 uses CTA-861-G
* this uses EDID 1.4 structure * this uses EDID 1.4 structure
* EDID 1.3/1.4 is 128 bytes long, and can point to 128 bytes extension * 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 * 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) 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 (1 == edid[18]) { // EDID 1.3/1.4 128-byte structure
if (checksum_ok(&edid[0], 128)) { if (checksum_ok(&edid[0], 128)) { // ensure checksum of base EDID is ok
if (0 == edid[126]) { // no extension const uint16_t length = 128 + (1 + edid[126]) * 128; // get length with all extensions
puts("128 bytes\r\n"); puts("(v1.4 ");
return 128; putn(edid[126] / 100);
} else { // extension available putn((edid[126] / 10) % 10);
// the usual extension is CEA EDID Timing Extension (with extension tag 02), but we allow others putn(edid[126] % 10);
// no idea how more than 1 extension is supported puts(" extension) ");
if (checksum_ok(&edid[128], 128)) { for (uint16_t i = 128; i < length && i < 256; i += 128) { // verify checksum of each extension (we actually only support one extension)
puts("256 bytes (with extension)\r\n"); if (!checksum_ok(&edid[i], 128)) {
return 256;
} else {
puts("extension CRC error\r\n"); puts("extension CRC error\r\n");
return 0; // EDID is broken return 0; // EDID is broken
} }
} }
puts("CRC ok\r\n");
return length;
} else { } else {
puts("CRC error\r\n"); puts("base CRC error\r\n");
return 0; return 0;
} }
} else if (2 == edid[18]) { // EDID 2.0 256-byte structure } else if (2 == edid[18]) { // EDID 2.0 256-byte structure
if (checksum_ok(&edid[0], 256)) { if (checksum_ok(&edid[0], 256)) {
puts("256 bytes (no extension)\r\n"); puts("(v2) CRC ok\r\n");
return 256; return 256;
} else { } else {
puts("CRC error\r\n"); puts("CRC error\r\n");