fdcan: Add support for enabling TDC (Transceiver Delay Compensation)

Transceiver Delay Compensation is required for reliable CAN FD data
phase operation at high bitrates (5+ Mbps).

Author: andoma

src/platform/stm32/stm32_fdcan.c

@@ -1,5 +1,7 @@
 #include "irq.h"
 
+#include "stm32_fdcan.h"
+
 #include <assert.h>
 
 #include <mios/eventlog.h>
@@ -14,6 +16,8 @@
 
 #include <mios/bytestream.h>
 
+#define FDCAN_TDCR  0x048
+
 #define FDCAN_FLSSA(x)     (0x000 + 4 * (x))
 #define FDCAN_FLESA         0x070
 #define FDCAN_RXFIFO0(x,y) (0x0b0 + 72 * (x) + 4 * (y))
@@ -343,7 +347,8 @@ stm32_fdcan_init(fdcan_t *fc, const char *name,
                  uint32_t nominal_bitrate, uint32_t data_bitrate,
                  uint32_t clockfreq,
                  const struct dsig_filter *dif,
-                 const struct dsig_filter *dof)
+                 const struct dsig_filter *dof,
+                 uint32_t flags)
 {
   int stdidx = 0;
 
@@ -396,6 +401,7 @@ stm32_fdcan_init(fdcan_t *fc, const char *name,
 
   can_timing_t nom, data;
   error_t err;
+
   err = fdcan_calculate_timings(clockfreq, nominal_bitrate, 75,
                                 512, 256, 128, &nom, "nominal");
   if(err)
@@ -406,12 +412,22 @@ stm32_fdcan_init(fdcan_t *fc, const char *name,
   if(err)
     return err;
 
-  reg_wr(fc->reg_base + FDCAN_DBTP,
-         ((data.prescaler - 1) << 16) |
-         ((data.t1 - 1) << 8) |
-         ((data.t2 - 1) << 4) |
-         ((data.t2 - 1) << 0) |
-         0);
+  uint32_t dbtp =
+    ((data.prescaler - 1) << 16) |
+    ((data.t1 - 1) << 8) |
+    ((data.t2 - 1) << 4) |
+    ((data.t2 - 1) << 0) |
+    0;
+
+  if(flags & FDCAN_ENABLE_TDC) {
+    // TDCO: SSP offset in CAN clock cycles = sample point position
+    const int tdco = (1 + data.t1) * data.prescaler;
+    reg_wr(fc->reg_base + FDCAN_TDCR, tdco << 8);
+
+    dbtp |= (1 << 23); // TDC: Transceiver Delay Compensation;
+  }
+
+  reg_wr(fc->reg_base + FDCAN_DBTP, dbtp);
 
   reg_wr(fc->reg_base + FDCAN_NBTP,
          ((nom.prescaler - 1) << 16) |

src/platform/stm32/stm32_fdcan.h

@@ -0,0 +1,3 @@
+#pragma once
+
+#define FDCAN_ENABLE_TDC        0x1

src/platform/stm32h7/stm32h7_can.c

@@ -126,7 +126,8 @@ stm32h7_can_init(int instance, gpio_t can_tx, gpio_t can_rx,
                                  nominal_bitrate, data_bitrate,
                                  clk_get_freq(CLK_FDCAN),
                                  input_filter,
-                                 output_filter);
+                                 output_filter,
+                                 flags);
   if(err) {
     printf("%s: Failed to initialize\n", name);
     return NULL;

src/platform/stm32h7/stm32h7_can.h

@@ -5,7 +5,9 @@
 struct dsig_filter;
 struct can_netif;
 
-#define STM32H7_CAN_TIM3_TIMESTAMPING 0x1
+#include "platform/stm32/stm32_fdcan.h"
+
+#define STM32H7_CAN_TIM3_TIMESTAMPING 0x10000
 
 struct can_netif *stm32h7_can_init(int instance, gpio_t can_tx, gpio_t can_rx,
                                    unsigned int nominal_bitrate,

src/platform/t234spe/t234spe_can.c

@@ -91,7 +91,8 @@ tegra243_spe_can_init(unsigned int nominal_bitrate,
                                  nominal_bitrate, data_bitrate,
                                  50000000,
                                  input_filter,
-                                 output_filter);
+                                 output_filter,
+                                 flags);
   if(err) {
     printf("%s: Failed to initialize\n", name);
     return NULL;

src/platform/t234spe/t234spe_can.h

@@ -5,6 +5,8 @@
 struct dsig_filter;
 struct can_netif;
 
+#include "platform/stm32/stm32_fdcan.h"
+
 struct can_netif *tegra243_spe_can_init(unsigned int nominal_bitrate,
                                         unsigned int data_bitrate,
                                         const struct dsig_filter *input_filter,