Feature STM8 Soft UART support by vshcryabets · Pull Request #58 · vshcryabets/V2StyxLib

vshcryabets · 2026-03-19T21:25:54Z

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…dd delay function

Copilot

Pull request overview

Adds optional STM8 software-based UART TX support and refactors UART configuration flags to support the new mode.

Changes:

Extend UART config to include a “soft UART TX” option and rename config flag macros.
Implement STM8 software UART TX path and route UART sends through a shared send_byte helper.
Update PlatformIO srcFilter and adjust README content.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
c/l4/src/Channel_c.c	Adds soft-UART-TX config option and switches to renamed config-bit macros.
c/l4/src/ChannelUartStm8.c	Implements soft UART TX bit-banging and refactors STM8 UART send/setup APIs.
c/l4/library.json	Ensures `Channel_c.c` is included in the build filter.
c/l4/include/Channel_c.h	Renames/extends config-bit macros and updates configure API signature.
c/l4/include/ChannelUartStm8.h	Introduces STM8-specific config struct and updates function signatures.
c/l4/README.md	Updates documentation, adding a soft-UART TX section (currently mismatched with code symbols).

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Copilot · 2026-03-19T21:30:06Z

+    V2styxlibUartConfig baseConfig;
+#ifdef V2STYXLIB_SOFTUART    
+    GPIO_TypeDef * softUartPort;
+    int8_t softUartTxPinMask;


softUartTxPinMask is used as a bitmask for GPIO registers, but it is declared as int8_t. Using a signed type for bitmasks is error-prone (sign-extension during promotions, unclear valid range). Prefer an unsigned type (e.g., uint8_t) consistent with the STM8 GPIO register widths.

Suggested change

int8_t softUartTxPinMask;

uint8_t softUartTxPinMask;

Copilot · 2026-03-19T21:30:07Z

+#define V2STYXLIB_CONFIG_STREAMING_MODE 0x01
+#define V2STYXLIB_CONFIG_SEND_CRC16 0x02
+#define V2STYXLIB_CONFIG_SOFT_UART_TX 0x04



The config-bit macros are now unconditionally defined and the previous V2STYXLIB_STREAMING_MODE / V2STYXLIB_SEND_CRC16 names were removed. This is an API-breaking change and also prevents users from redefining these macros (the README states these values can be redefined, and CRC macros still use #ifndef). Consider restoring override-ability via #ifndef and/or providing backward-compatible aliases for the old macro names.

Suggested change

#define V2STYXLIB_CONFIG_STREAMING_MODE 0x01

#define V2STYXLIB_CONFIG_SEND_CRC16 0x02

#define V2STYXLIB_CONFIG_SOFT_UART_TX 0x04

#ifndef V2STYXLIB_CONFIG_STREAMING_MODE

#define V2STYXLIB_CONFIG_STREAMING_MODE 0x01

#endif

#ifndef V2STYXLIB_CONFIG_SEND_CRC16

#define V2STYXLIB_CONFIG_SEND_CRC16 0x02

#endif

#ifndef V2STYXLIB_CONFIG_SOFT_UART_TX

#define V2STYXLIB_CONFIG_SOFT_UART_TX 0x04

#endif

/* Backward-compatible aliases for previous macro names */

#ifndef V2STYXLIB_STREAMING_MODE

#define V2STYXLIB_STREAMING_MODE V2STYXLIB_CONFIG_STREAMING_MODE

#endif

#ifndef V2STYXLIB_SEND_CRC16

#define V2STYXLIB_SEND_CRC16 V2STYXLIB_CONFIG_SEND_CRC16

#endif

Copilot · 2026-03-19T21:30:07Z

+## `V2STYXLIB_SOFTUART_TX`
+
+Enables the use of Software UART for TX on STM8. This is particularly useful when 
+you need additional ADC channels and want to free up the **UART1_TX / AIN5 / (HS) PD5** pin for analog input.
+
+**Note:** This implementation covers TX only, as software-based RX is generally 
+unstable on this architecture due to timing constraints.


README documents V2STYXLIB_SOFTUART_TX, but the code uses a compile-time switch V2STYXLIB_SOFTUART and a config flag V2STYXLIB_CONFIG_SOFT_UART_TX. This mismatch will confuse users and makes the documented macro ineffective. Please update the README to reference the actual symbols and (since streaming/CRC flags still exist) document the config-bit flags for streaming mode/CRC16 as well.

Copilot · 2026-03-19T21:30:07Z

+}
+
+void v2styxlib_uart_setup(
+    const V2styxlibUartStm8Config* config,`


There is an extraneous '`' character in the v2styxlib_uart_setup parameter list, which will cause a compilation error. Remove the stray character so the function signature matches the header declaration.

Suggested change

const V2styxlibUartStm8Config* config,`

const V2styxlibUartStm8Config* config,

Copilot · 2026-03-19T21:30:08Z

+void v2styxlib_delay_bit() {
+    __asm
+        pushw x         
+        ldw x, #535 ; hardcode for 9600 baud at 16 MHz, adjust if needed
+    00001$:


v2styxlib_delay_bit() is hardcoded for 9600 baud @ 16 MHz, but v2styxlib_uart_setup() accepts an arbitrary baudRateDivider and the rest of the driver configures UART1 based on that divider. When soft UART TX is enabled, TX timing will not match the configured baud rate unless the delay is derived from baudRateDivider/F_CPU (or the API explicitly documents that soft TX only supports a fixed baud).

Copilot · 2026-03-19T21:30:08Z

+#ifdef V2STYXLIB_SOFTUART
+    if (config->baseConfig.config & V2STYXLIB_CONFIG_SOFT_UART_TX) {
+        // Send byte using software UART
+        // Start bit
+        config->softUartPort->ODR &= ~config->softUartTxPinMask;
+        v2styxlib_delay_bit();
+
+        // Data bits (LSB first)
+        for (uint8_t i = 0; i < 8; i++) {
+            if (byte & 0x01) {
+                config->softUartPort->ODR |= config->softUartTxPinMask;
+            } else {
+                config->softUartPort->ODR &= ~config->softUartTxPinMask;
+            }
+            byte >>= 1;
+            v2styxlib_delay_bit();
+        }


Soft UART TX bit-banging here is timing-sensitive, but the transmit loop does not guard against interrupts/preemption. Any ISR latency during v2styxlib_delay_bit() will skew bit timing and can corrupt bytes. Consider disabling interrupts around the start/data/stop bit sequence (or using a timer-driven delay) to keep bit periods stable.

Copilot · 2026-03-19T21:30:08Z

+#ifdef V2STYXLIB_SOFTUART
+void v2styxlib_delay_bit() {
+    __asm
+        pushw x         
+        ldw x, #535 ; hardcode for 9600 baud at 16 MHz, adjust if needed
+    00001$:
+        decw x  
+        jrne 00001$  
+        popw x  
+    __endasm;
+}
+#endif
+
+void v2styxlib_send_byte(
+    const V2styxlibUartStm8Config* config,
+    uint8_t byte) {


v2styxlib_delay_bit() / v2styxlib_send_byte() appear to be internal helpers (not declared in the public header) but are currently exported as global symbols. Mark them static (and optionally inline for send_byte if appropriate) to avoid namespace pollution and potential symbol collisions in embedded builds.

Copilot

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

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Copilot · 2026-03-19T21:42:02Z

 void v2styxlib_uart_configure_proto(
    V2styxlibUartConfig *config,
    bool useStreamingMode,
-    bool sendCrc16
+    bool sendCrc16,
+    bool useSoftUartTx
 );


This change is a breaking API update: v2styxlib_uart_configure_proto now requires an additional argument and the config bit macros were renamed. In this repo, cpp/modules/l4/src/styxpico/ChannelUsbUart.cpp still calls the 3-arg function and uses V2STYXLIB_STREAMING_MODE/V2STYXLIB_SEND_CRC16, which will no longer compile against this header. Either update all in-repo call sites and macro uses, or provide backward-compatible aliases/wrappers (e.g., deprecated defines mapping old names to new ones and a compatibility function/macro that defaults useSoftUartTx to false).

Copilot · 2026-03-19T21:42:03Z

+## `V2STYXLIB_SOFTUART_TX`
+
+Enables the use of Software UART for TX on STM8. This is particularly useful when 
+you need additional ADC channels and want to free up the **UART1_TX / AIN5 / (HS) PD5** pin for analog input.
+


The README documents V2STYXLIB_SOFTUART_TX, but the actual runtime config bit added in Channel_c.h is V2STYXLIB_CONFIG_SOFT_UART_TX, and the STM8 soft-UART code is compiled under V2STYXLIB_SOFTUART. Please align the documentation with the real macro/flag names (and ideally mention both the compile-time switch and the runtime config bit).

Suggested change

## `V2STYXLIB_SOFTUART_TX`

Enables the use of Software UART for TX on STM8. This is particularly useful when

you need additional ADC channels and want to free up the **UART1_TX / AIN5 / (HS) PD5** pin for analog input.

## `V2STYXLIB_SOFTUART`

Compile-time switch that enables the Software UART implementation for TX on STM8. This is particularly useful when

you need additional ADC channels and want to free up the **UART1_TX / AIN5 / (HS) PD5** pin for analog input.

At runtime, the `V2STYXLIB_CONFIG_SOFT_UART_TX` configuration bit controls whether soft-UART TX is enabled on a given channel.

Copilot · 2026-03-19T21:42:03Z

+        __asm
+            sim ; disable interrupts (software UART timing)
+        __endasm;
+        config->softUartPort->ODR &= ~config->softUartTxPinMask;


Disabling interrupts with sim and then unconditionally re-enabling with rim can break callers that entered this function with interrupts already disabled (it will unexpectedly enable them). Preserve and restore the prior interrupt state (e.g., save/restore CC) instead of always calling rim at the end.

vshcryabets added 2 commits March 19, 2026 21:37

Add Software UART support for STM8 and refactor UART configuration

14abb1a

Refactor soft UART implementation for STM8: update pin handling and a…

9012896

…dd delay function

vshcryabets requested a review from Copilot March 19, 2026 21:25

vshcryabets self-assigned this Mar 19, 2026

Copilot started reviewing on behalf of vshcryabets March 19, 2026 21:26 View session

Copilot AI reviewed Mar 19, 2026

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1d1ed8f

vshcryabets requested a review from Copilot March 19, 2026 21:37

Copilot started reviewing on behalf of vshcryabets March 19, 2026 21:37 View session

Copilot AI reviewed Mar 19, 2026

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vshcryabets merged commit dbf3f39 into master Mar 19, 2026
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vshcryabets deleted the feature/stm8-soft-uart branch May 17, 2026 13:33

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Feature STM8 Soft UART support#58

Feature STM8 Soft UART support#58
vshcryabets merged 3 commits into
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feature/stm8-soft-uart

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-#define V2STYXLIB_CONFIG_STREAMING_MODE 0x01
-#define V2STYXLIB_CONFIG_SEND_CRC16 0x02
-#define V2STYXLIB_CONFIG_SOFT_UART_TX 0x04
+#ifndef V2STYXLIB_CONFIG_STREAMING_MODE
+    #define V2STYXLIB_CONFIG_STREAMING_MODE 0x01
+#endif
+#ifndef V2STYXLIB_CONFIG_SEND_CRC16
+    #define V2STYXLIB_CONFIG_SEND_CRC16 0x02
+#endif
+#ifndef V2STYXLIB_CONFIG_SOFT_UART_TX
+    #define V2STYXLIB_CONFIG_SOFT_UART_TX 0x04
+#endif
+/* Backward-compatible aliases for previous macro names */
+#ifndef V2STYXLIB_STREAMING_MODE
+    #define V2STYXLIB_STREAMING_MODE V2STYXLIB_CONFIG_STREAMING_MODE
+#endif
+#ifndef V2STYXLIB_SEND_CRC16
+    #define V2STYXLIB_SEND_CRC16 V2STYXLIB_CONFIG_SEND_CRC16
+#endif

	const V2styxlibUartStm8Config* config,`
	const V2styxlibUartStm8Config* config,

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