From 2859bb7a09f00a0468e68c018ab276d235bf0602 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?King=20K=C3=A9vin?= <kingkevin@cuvoodoo.info>
Date: Mon, 11 Jul 2022 12:26:28 +0200
Subject: [PATCH] check if HPD is forwarded

---
 main.c | 43 ++++++++++++++++++++++++++-----------------
 1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/main.c b/main.c
index 1e87483..f393dc1 100644
--- a/main.c
+++ b/main.c
@@ -26,6 +26,7 @@ static bool i2c_fwd = false; // if the I²C source lines are connected to sink
 // hot plug detect pull up
 #define HPD_PORT GPIO_PC
 #define HPD_PIN PC6
+static bool hpd_fwd = false; // if the I²C source line is connected to sink
 // copy EDID setting
 #define EDID_PORT GPIO_PC
 #define EDID_PIN PC7
@@ -136,13 +137,16 @@ void main(void)
 		SCL_PU_PORT->ODR.reg |= SCL_PU_PIN; // pull up SCL line
 	}
 
-	// configure external EEPROM (actually not used)
-	WP_PORT->DDR.reg |= WP_PIN; // switch pin to output
-	WP_PORT->CR1.reg &= ~WP_PIN; // switch pin to open drain
-	WP_PORT->ODR.reg |= WP_PIN; // let write protect pulled up
-
 	// configure I²C
 	if (!i2c_fwd) { // we will act as I²C slave EEPROM
+/*
+HDMI 1.3 spec:
+The Sink shall be capable of responding with EDID 1.3 data and up to 255 extension blocks, each 128 bytes long (up to 32K bytes total E-EDID memory) whenever the Hot Plug Detect signal is asserted.
+The Sink should be capable of providing E-EDID information over the Enhanced DDC channel whenever the +5V Power signal is provided. This should be available within 20msec after the +5V Power signal is provided.
+
+firewall:
+we will only be able to provide 1 extension block since we can only respond to one I²C address 0x50 for the EDID, and not to the 0x30 Segment Pointer (for the other pages/extension blocks)
+*/
 		GPIO_PB->CR1.reg |= (PB4 | PB5); // enable internal pull-up on SCL/SDA
 		GPIO_PB->DDR.reg &= ~(PB4 | PB5); // set SCL/SDA as input before it is used as alternate function by the peripheral
 		I2C_CR1 |= I2C_CR1_PE; // enable I²C peripheral (must be done before any other register is written)
@@ -159,20 +163,25 @@ void main(void)
 		I2C_ITR |= (I2C_ITR_ITBUFEN | I2C_ITR_ITEVTEN); // enable buffer and event interrupts
 	}
 
+	// configure external EEPROM (actually not used)
+	WP_PORT->DDR.reg |= WP_PIN; // switch pin to output
+	WP_PORT->CR1.reg &= ~WP_PIN; // switch pin to open drain
+	WP_PORT->ODR.reg |= WP_PIN; // let write protect pulled up
+
 	// configure hot plug detect
 	HPD_PORT->DDR.reg |= HPD_PIN; // switch pin to output
-	HPD_PORT->CR1.reg |= HPD_PIN; // switch pin to push pull
-	HPD_PORT->ODR.reg |= HPD_PIN; // pull up HPD line to indicate EDID is ready
-	// TODO check if connected to sink/monitor
-
-/*
-The Sink shall be capable of responding with EDID 1.3 data and up to 255 extension blocks, each
-128 bytes long (up to 32K bytes total E-EDID memory) whenever the Hot Plug Detect signal is
-asserted.
-The Sink should be capable of providing E-EDID information over the Enhanced DDC channel
-whenever the +5V Power signal is provided. This should be available within 20msec after the +5V
-Power signal is provided.
-*/
+	HPD_PORT->CR1.reg &= ~HPD_PIN; // switch pin to open drain
+	HPD_PORT->ODR.reg &= ~HPD_PIN; // drain line
+	wait_10us(0); // wait shortly to clear tristate
+	HPD_PORT->DDR.reg &= ~HPD_PIN; // switch pin to input (already floating)
+	if (HPD_PORT->IDR.reg & HPD_PIN) { // line is pulled up
+		hpd_fwd = true; // remember the HPD line is pulled up
+	}
+	if (!hpd_fwd) { // we have to pull up
+		HPD_PORT->DDR.reg |= HPD_PIN; // switch pin to output
+		HPD_PORT->CR1.reg |= HPD_PIN; // switch pin to push pull
+		HPD_PORT->ODR.reg |= HPD_PIN; // pull up HPD line to indicate EDID is ready
+	}
 
 	// check if EDID should be copied
 	EDID_PORT->DDR.reg &= ~EDID_PIN; // switch pin to output