force builder to specifiy GPU vendor

there is no single default for the I2C wait time
that will not crash any Macintoshes.

patches welcome for runtime GPU detection! (#57)

relates to #1 #18 #35 #42 #57

DDC.c

@@ -210,7 +210,11 @@ bool DDCRead(CGDirectDisplayID displayID, struct DDCReadCommand *read) {
         request.sendBytes                       = 5;
         // Certain displays / graphics cards require a long-enough delay to give a response.
         // Relying on retry will not help if the delay is too short.
-        request.minReplyDelay                   = 30 * kMillisecondScale;  // too short can freeze kernel
+        request.minReplyDelay                   = kDDCMinReplyDelay * kNanosecondScale;
+		// FIXME: this should be tuneable at runtime
+		// https://github.com/kfix/-vendorddcctl/issues/57
+		// incorrect values for GPU-vendor can cause kernel panic
+		// https://developer.apple.com/documentation/iokit/ioi2crequest/1410394-minreplydelay?language=objc
 
         data[0] = 0x51;
         data[1] = 0x82;

Makefile

@@ -1,26 +1,33 @@
 #!/bin/make -f
 
-CCFLAGS ?=
+CCFLAGS ?= -Wno-unused-variable
 
 ## Reply Transaction Type
 ## uncomment one only one
 ## comment both to use automatic detection
 #CCFLAGS += -DTT_DDC
 #CCFLAGS += -DTT_SIMPLE
 
-## Uncomment to use an external app 'OSDisplay' to have a BezelUI like OSD
+## Uncomment to use an external app 'OSDisplay' to have a BezelUI-like OSD
+##  provided by https://github.com/zulu-entertainment/OSDisplay
 #CCFLAGS += -DOSD
 
 all: clean ddcctl
 
+intel nvidia: CCFLAGS += -DkDDCMinReplyDelay=1
+intel nvidia: all
+
+amd: CCFLAGS += -DkDDCMinReplyDelay=30000000
+amd: all
+
 debug: CCFLAGS += -DDEBUG
 debug: clean ddcctl
 
 %.o: %.c
-	$(CC) $(CCFLAGS) -Wall -c -o $@ $<
+	$(CC) -Wall $(CCFLAGS) -c -o $@ $<
 
 ddcctl: DDC.o
-	$(CC) $(CCFLAGS) -Wall -o $@ -lobjc -framework IOKit -framework AppKit -framework Foundation $< $@.m
+	$(CC) -Wall $(CCFLAGS) -o $@ -lobjc -framework IOKit -framework AppKit -framework Foundation $< $@.m
 
 install: ddcctl
 	install ddcctl /usr/local/bin
@@ -34,4 +41,4 @@ framebuffers:
 displaylist:
 	ioreg -c IODisplayConnect -b -f -r -l -i -d 2
 
-.PHONY: all clean install displaylist
+.PHONY: all clean install displaylist amd intel nvidia

README.md

@@ -14,9 +14,9 @@ And *possibly* (if your monitor firmware is well implemented):
 
 Install
 ----
-```bash
-make install
-```
+* install Xcode
+* figure out if your Mac is using an Intel, Nvidia or AMD gpu
+* run `make intel` or make `make nvidia` or `make amd`
 
 Usage
 ----