feat(uart): baud rate calculation

wokwi · Oct 2, 2023 · 1408874 · 1408874
1 parent 4edfa0c
commit 1408874
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Showing 2 changed files with 37 additions and 0 deletions.
diff --git a/src/peripherals/uart.spec.ts b/src/peripherals/uart.spec.ts
@@ -2,6 +2,8 @@ import { describe, expect, it } from 'vitest';
 import { RP2040 } from '../rp2040.js';
 import { RPUART } from './uart.js';
 
+const UARTIBRD = 0x24;
+const UARTFBRD = 0x28;
 const OFFSET_UARTLCR_H = 0x2c;
 
 describe('UART', () => {
@@ -11,4 +13,12 @@ describe('UART', () => {
     uart.writeUint32(OFFSET_UARTLCR_H, 0x70);
     expect(uart.wordLength).toEqual(8);
   });
+
+  it('should correctly calculate the baud rate based on UARTIBRD, UARTFBRD values', () => {
+    const rp2040 = new RP2040();
+    const uart = new RPUART(rp2040, 'UART', 0, { rx: 0, tx: 0 });
+    uart.writeUint32(UARTIBRD, 67); // Values taken from example in section 4.2.7.1. of the datasheet
+    uart.writeUint32(UARTFBRD, 52);
+    expect(uart.baudRate).toEqual(115207);
+  });
 });
diff --git a/src/peripherals/uart.ts b/src/peripherals/uart.ts
@@ -5,6 +5,8 @@ import { BasePeripheral, Peripheral } from './peripheral.js';
 
 const UARTDR = 0x0;
 const UARTFR = 0x18;
+const UARTIBRD = 0x24;
+const UARTFBRD = 0x28;
 const UARTLCR_H = 0x2c;
 const UARTCR = 0x30;
 const UARTIMSC = 0x38;
@@ -39,8 +41,11 @@ export class RPUART extends BasePeripheral implements Peripheral {
   private rxFIFO = new FIFO(32);
   private interruptMask = 0;
   private interruptStatus = 0;
+  private intDivisor = 0;
+  private fracDivisor = 0;
 
   public onByte?: (value: number) => void;
+  public onBaudRateChange?: (baudRate: number) => void;
 
   constructor(
     rp2040: RP2040,
@@ -83,6 +88,14 @@ export class RPUART extends BasePeripheral implements Peripheral {
     }
   }
 
+  get baudDivider() {
+    return this.intDivisor + this.fracDivisor / 64;
+  }
+
+  get baudRate() {
+    return Math.round(this.rp2040.clkPeri / (this.baudDivider * 16));
+  }
+
   get flags() {
     return (this.rxFIFO.full ? RXFF : 0) | (this.rxFIFO.empty ? RXFE : 0) | TXFE;
   }
@@ -110,6 +123,10 @@ export class RPUART extends BasePeripheral implements Peripheral {
       }
       case UARTFR:
         return this.flags;
+      case UARTIBRD:
+        return this.intDivisor;
+      case UARTFBRD:
+        return this.fracDivisor;
       case UARTLCR_H:
         return this.lineCtrlRegister;
       case UARTCR:
@@ -130,6 +147,16 @@ export class RPUART extends BasePeripheral implements Peripheral {
         this.onByte?.(value & 0xff);
         break;
 
+      case UARTIBRD:
+        this.intDivisor = value & 0xffff;
+        this.onBaudRateChange?.(this.baudRate);
+        break;
+
+      case UARTFBRD:
+        this.fracDivisor = value & 0x3f;
+        this.onBaudRateChange?.(this.baudRate);
+        break;
+
       case UARTLCR_H:
         this.lineCtrlRegister = value;
         break;