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Fix HDMI receive frame acknowledge timing. (#2)
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* Fix HDMI receive frame acknowledge timing.

During the ACK bit, pull the line to low impedance at the start.
The HDMI v1.3a specification requires low impedance from the follower no
later than T1 == 0.35ms after start of bit.

Reduce the idle time before frame transmission to 7 bit times.

Whilst here, add additional responses:
* broadcast physical address
* broadcast device vendor ID
* on routing change, broadcast image view on

* Update real-world usage in README.
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@gkoh
gkoh authored Jul 22, 2024
1 parent e0160c0 commit e2cef6c
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Showing 2 changed files with 54 additions and 26 deletions.
2 changes: 2 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,8 @@ This is currently working with:
* through a Denon AVR connected to the Sharp TV (physical address 0x1100)
* Pico-CEC connected to Denon AVR HDMI input 1
* Denon AVR connected to TV HDMI input 1
* a Sony 60" TV (physical address 0x1000)
* directly connected to TV HDMI input 1

# Design
## Hardware
Expand Down
78 changes: 52 additions & 26 deletions src/hdmi-cec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -163,22 +163,21 @@ static void hdmi_rx_frame_isr(uint gpio, uint32_t events) {
return;
case HDMI_FRAME_STATE_ACK_LOW:
rx_frame.start = time_us_64();
// send ack by changing ack from 1 to 0
uint8_t tgt_addr = rx_frame.message->data[0] & 0x0f;
if ((tgt_addr != 0x0f) && (tgt_addr == rx_frame.address)) {
rx_frame.state = HDMI_FRAME_STATE_ACK_END;
gpio_set_dir(CEC_PIN, GPIO_OUT); // pull low, then schedule pull high
add_alarm_at(from_us_since_boot(rx_frame.start + 1500), ack_high, NULL, true);
rx_frame.ack = true;
}
rx_frame.state = HDMI_FRAME_STATE_ACK_HIGH;
gpio_set_irq_enabled(CEC_PIN, GPIO_IRQ_EDGE_RISE, true);
return;
case HDMI_FRAME_STATE_ACK_HIGH:
low_time = time_us_64() - rx_frame.start;
if (low_time >= 400 && low_time <= 800) {
// send ack by changing ack from 1 to 0
uint8_t tgt_addr = rx_frame.message->data[0] & 0x0f;
if ((tgt_addr != 0x0f) && (tgt_addr == rx_frame.address)) {
rx_frame.state = HDMI_FRAME_STATE_ACK_END;
gpio_set_dir(CEC_PIN, GPIO_OUT); // pull low, then schedule pull high
add_alarm_at(from_us_since_boot(rx_frame.start + 1500), ack_high, NULL, true);
// interrupt ourselves
gpio_set_irq_enabled(CEC_PIN, GPIO_IRQ_EDGE_RISE, true);
return;
}
if ((low_time >= 400 && low_time <= 800) || (low_time >= 1300 && low_time <= 1700)) {
rx_frame.state = HDMI_FRAME_STATE_ACK_END;
} else {
rx_frame.state = HDMI_FRAME_STATE_ABORT;
xTaskNotifyIndexedFromISR(xCECTask, NOTIFY_RX, 0, eNoAction, NULL);
Expand All @@ -205,14 +204,15 @@ static uint8_t recv_frame(uint8_t *pld, uint8_t address) {
// printf("recv_frame\n");
rx_frame.address = address;
rx_frame.state = HDMI_FRAME_STATE_START_LOW;
rx_frame.ack = false;
memset(&rx_frame.message->data[0], 0, 16);
gpio_set_irq_enabled(CEC_PIN, GPIO_IRQ_EDGE_FALL, true);
ulTaskNotifyTakeIndexed(NOTIFY_RX, pdTRUE, portMAX_DELAY);
memcpy(pld, rx_frame.message->data, rx_frame.message->len);
printf("high water mark = %lu\n", uxTaskGetStackHighWaterMark(xCECTask));
// printf("high water mark = %lu\n", uxTaskGetStackHighWaterMark(xCECTask));

if (rx_frame.state == HDMI_FRAME_STATE_ABORT) {
printf("ABORT\n");
// printf("ABORT\n");
return 0;
}

Expand Down Expand Up @@ -291,8 +291,8 @@ static int64_t hdmi_tx_callback(alarm_id_t alarm, void *user_data) {
static bool hdmi_tx_frame(uint8_t *data, uint8_t len) {
unsigned char i = 0;

// wait 13 bit times of idle before sending
while (i < 13) {
// wait 7 bit times of idle before sending
while (i < 7) {
vTaskDelay(pdMS_TO_TICKS(2.4));
if (gpio_get(CEC_PIN)) {
i++;
Expand All @@ -311,7 +311,7 @@ static bool hdmi_tx_frame(uint8_t *data, uint8_t len) {
.state = HDMI_FRAME_STATE_START_LOW};
add_alarm_at(from_us_since_boot(time_us_64()), hdmi_tx_callback, &frame, true);
ulTaskNotifyTakeIndexed(NOTIFY_TX, pdTRUE, portMAX_DELAY);
printf("high water mark = %lu\n", uxTaskGetStackHighWaterMark(xCECTask));
// printf("high water mark = %lu\n", uxTaskGetStackHighWaterMark(xCECTask));
return frame.ack;
}

Expand Down Expand Up @@ -388,29 +388,34 @@ static void report_physical_address(uint8_t initiator,
(physical_address >> 0) & 0x0ff, device_type};

send_frame(5, pld);
printf("\n<-- %02x:84 [Report Physical Address]", pld[0]);
printf("\n<-- %02x:84 [Report Physical Address] %02x%02x", pld[0], pld[2], pld[3]);
}

static void report_cec_version(uint8_t initiator, uint8_t destination) {
// 0x04 = 1.3a
uint8_t pld[3] = {HEADER0(initiator, destination), 0x9e, 0x04};
send_frame(3, pld);
printf("\n<-- %02x: 9e [CEC Version]", pld[0]);
printf("\n<-- %02x:9e [CEC Version]", pld[0]);
}

static bool ping(uint8_t destination) {
uint8_t pld[1] = {HEADER0(destination, destination)};

bool ack = send_frame(1, pld);
printf("ack = %d\n", ack);
return ack;
return send_frame(1, pld);
}

static void image_view_on(uint8_t initiator, uint8_t destination) {
uint8_t pld[2] = {HEADER0(initiator, destination), 0x04};

send_frame(2, pld);
printf("\n<-- %02x:04 [Image View On]", pld[0]);
}

static uint8_t allocate_logical_address(void) {
uint8_t a;
for (unsigned int i = 0; i < NUM_ADDRESS; i++) {
a = address[i];
printf("Attempting to allocate logical address 0x%02x\n", a);
printf("\nAttempting to allocate logical address 0x%02x\n", a);
if (!ping(a)) {
break;
}
Expand Down Expand Up @@ -440,10 +445,11 @@ void cec_task(void *data) {
uint8_t key = HID_KEY_NONE;

pldcnt = recv_frame(pld, l_address);
printf("pldcnt = %u\n", pldcnt);
// printf("pldcnt = %u\n", pldcnt);
pldcntrcvd = pldcnt;
initiator = (pld[0] & 0xf0) >> 4;
destination = pld[0] & 0x0f;
printf("%02x -> %02x: ", initiator, destination);

if ((pldcnt > 1)) {
switch (pld[1]) {
Expand Down Expand Up @@ -478,18 +484,31 @@ void cec_task(void *data) {
case 0x7e:
printf("[System Audio Mode Status]");
break;
case 0x80:
printf("[Routing Change]");
image_view_on(l_address, 0x00);
break;
case 0x82:
printf("[Active Source]");
printf("[Active Source]\n");
printf("<*> [Turn the display ON]");
break;
case 0x84:
printf("[Report Physical Address>]");
printf("[Report Physical Address>] %02x%02x", pld[2], pld[3]);
// On broadcast receive, do the same
if ((initiator == 0x00) && (destination == 0x0f)) {
// l_address = allocate_logical_address();
report_physical_address(l_address, 0x0f, CEC_PHYS_ADDR, DEFAULT_TYPE);
}
break;
case 0x85:
printf("[Request Active Source]");
break;
case 0x87:
printf("[Device Vendor ID]");
// On broadcast receive, do the same
if ((initiator == 0x00) && (destination == 0x0f)) {
device_vendor_id(l_address, 0x0f, 0x0010FA);
}
break;
case 0x8c:
printf("[Give Device Vendor ID]");
Expand Down Expand Up @@ -566,6 +585,14 @@ void cec_task(void *data) {
break;
case 0xFF:
printf("[Abort]");
break;
case 0xA0:
printf("[Vendor Command with ID]");
for (int i = 0; i < pldcnt; i++) {
printf(" %02x", pld[i]);
}
printf("\n");
break;
default:
if (pldcntrcvd > 1)
printf("???: %x", pld[1]); // undecoded command
Expand All @@ -575,7 +602,6 @@ void cec_task(void *data) {
} else {
// single byte polling message
printf("[Polling Message]: 0x%01x -> 0x%01x\n", initiator, destination);
// report_physical_address(l_address, 0x0f, 0x1000, DEFAULT_TYPE);
}
}
}

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