can2040: Improve bit time synchronization with slow transmitters

Increase the number of loops to check for a recessive to dominant transition. Signed-off-by: Kevin O'Connor <[email protected]>
KevinOConnor · Apr 29, 2023 · 760632f · 760632f
1 parent 1deea5e
commit 760632f
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Showing 2 changed files with 13 additions and 13 deletions.
diff --git a/pio/can2040.pio b/pio/can2040.pio
@@ -18,22 +18,22 @@
 
 // State machine "sync" code - clock and start/end of message signaling
 sync_recessive_edge:
-    jmp y--, sync_scan_edge     ; cp=31,33,35
-    jmp x--, sync_signal_sample ; cp=4
+    jmp y--, sync_scan_edge     ; cp=31,33,35,37
+    jmp x--, sync_signal_sample ; cp=6
 public sync_found_end_of_message:
-    set x, 10              [1]  ; cp=5
+    set x, 8               [1]  ; cp=7
 sync_loop_end_of_message:
     jmp pin sync_check_idle
 public sync_signal_start:
     irq set 0
 sync_scan_edge:
-    jmp pin sync_recessive_edge ; cp=30,32,34
+    jmp pin sync_recessive_edge ; cp=30,32,34,36
 public sync_entry:
     irq clear 0                 ; cp=1
 sync_got_dominant:
-    set x, 9               [2]  ; cp=2
+    set x, 9               [4]  ; cp=2
 sync_signal_sample:
-    set y, 2               [18] ; cp=5
+    set y, 3               [16] ; cp=7
     irq set 4              [1]  ; cp=24
     jmp pin sync_scan_edge [3]  ; cp=26
     jmp sync_got_dominant  [3]  ; cp=30
@@ -85,7 +85,7 @@ public tx_conflict:
 // Setup for "sync" state machine
 .program sm_sync_setup
     set pindirs, 0
-    // CPU pushes 106 into tx fifo - to set OSR for alternative slow start mode
+    // CPU pushes 104 into tx fifo - to set OSR for alternative slow start mode
     pull
     ;jmp sync_got_dominant
 
@@ -149,7 +149,7 @@ sync_signal_sample:
     jmp sync_got_dominant
 
 sync_scan_edge:
-    set y, 2
+    set y, 3
 sync_loop_scan_edge:
     jmp pin sync_recessive_edge
     jmp sync_got_dominant
@@ -159,7 +159,7 @@ sync_recessive_edge:
     jmp sync_found_end_of_message
 
 sync_found_end_of_message:
-    set x, 10
+    set x, 8
 sync_loop_end_of_message:
     jmp pin sync_check_idle
     jmp sync_signal_start

diff --git a/src/can2040.c b/src/can2040.c
@@ -84,13 +84,13 @@ rp2040_gpio_peripheral(uint32_t gpio, int func, int pull_up)
 static const uint16_t can2040_program_instructions[] = {
     0x0085, //  0: jmp    y--, 5
     0x0048, //  1: jmp    x--, 8
-    0xe12a, //  2: set    x, 10                  [1]
+    0xe129, //  2: set    x, 9                   [1]
     0x00cc, //  3: jmp    pin, 12
     0xc000, //  4: irq    nowait 0
     0x00c0, //  5: jmp    pin, 0
     0xc040, //  6: irq    clear 0
-    0xe229, //  7: set    x, 9                   [2]
-    0xf242, //  8: set    y, 2                   [18]
+    0xe429, //  7: set    x, 9                   [4]
+    0xf043, //  8: set    y, 3                   [16]
     0xc104, //  9: irq    nowait 4               [1]
     0x03c5, // 10: jmp    pin, 5                 [3]
     0x0307, // 11: jmp    7                      [3]
@@ -137,7 +137,7 @@ pio_sync_setup(struct can2040 *cd)
         | cd->gpio_rx << PIO_SM0_PINCTRL_SET_BASE_LSB);
     sm->instr = 0xe080; // set pindirs, 0
     sm->pinctrl = 0;
-    pio_hw->txf[0] = PIO_CLOCK_PER_BIT / 2 * 7 - 5 - 1;
+    pio_hw->txf[0] = 8 + 6 * PIO_CLOCK_PER_BIT / 2;
     sm->instr = 0x80a0; // pull block
     sm->instr = can2040_offset_sync_entry; // jmp sync_entry
 }