From bd68aba756b5d0cf9b52daea6ecdf0b512234524 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=2E=20Neusch=C3=A4fer?= <j.neuschaefer@gmx.net>
Date: Tue, 9 Jan 2024 02:39:43 +0100
Subject: [PATCH] Implement PIN_STATE command: Only set pins to output when
 requested

This has the advantage that the pico-serprog can stay attached to the
board even while a CPU etc. runs on the board and uses the flash.
---
 README.md   |  5 +++++
 main.c      | 14 +++++++++++---
 pio/spi.pio | 10 ++++++++--
 3 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index 62c227a..5ede88e 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,11 @@ Dump a flashchip:
 flashrom -p serprog:dev=/dev/ttyACM0:115200,spispeed=12M -r foo.bin
 ```
 
+pico-serprog only switches the pins to output when requested by flashrom. This
+means that you can leave your pico-serprog programmer attached to the flash;
+you don't have to detach it before booting the board that you're programming.
+
+
 ## License
 
 The project is based on the spi_flash example by Raspberry Pi (Trading) Ltd. which is licensed under BSD-3-Clause.
diff --git a/main.c b/main.c
index f6b907c..13ddf07 100644
--- a/main.c
+++ b/main.c
@@ -79,7 +79,14 @@ void putu32(uint32_t d) {
 
 unsigned char write_buffer[4096];
 
+void apply_pin_state(const pio_spi_inst_t *spi, bool state) {
+    pio_spi_enable_outputs(spi->pio, spi->sm, state, PIN_SCK, PIN_MOSI, PIN_MISO);
+    gpio_set_dir(PIN_CS, state? GPIO_OUT : GPIO_IN);
+}
+
 void process(const pio_spi_inst_t *spi, int command) {
+    static bool pin_state = false;
+
     switch(command) {
         case S_CMD_NOP:
             putchar(S_ACK);
@@ -155,14 +162,15 @@ void process(const pio_spi_inst_t *spi, int command) {
                 if (freq >= 1) {
                     putchar(S_ACK);
                     putu32(serprog_spi_init(freq));
+                    apply_pin_state(spi, pin_state);
                 } else {
                     putchar(S_NAK);
                 }
             }
             break;
         case S_CMD_S_PIN_STATE:
-            //TODO:
-            getchar();
+            pin_state = !!getchar();
+            apply_pin_state(spi, pin_state);
             putchar(S_ACK);
             break;
         default:
@@ -227,7 +235,7 @@ int main() {
     // Initialize CS
     gpio_init(PIN_CS);
     gpio_put(PIN_CS, 1);
-    gpio_set_dir(PIN_CS, GPIO_OUT);
+    gpio_set_dir(PIN_CS, GPIO_IN); // switch to output on S_CMD_S_PIN_STATE
 
     spi_offset = pio_add_program(spi.pio, &spi_cpha0_program);
     serprog_spi_init(1000000); // 1 MHz
diff --git a/pio/spi.pio b/pio/spi.pio
index 132c661..7dfc940 100644
--- a/pio/spi.pio
+++ b/pio/spi.pio
@@ -54,9 +54,9 @@ static inline void pio_spi_init(PIO pio, uint sm, uint prog_offs, uint n_bits,
     sm_config_set_in_shift(&c, false, true, n_bits);
     sm_config_set_clkdiv(&c, clkdiv);
 
-    // MOSI, SCK output are low, MISO is input
+    // MOSI, SCK output are low, MISO is input -- but we start in input mode
     pio_sm_set_pins_with_mask(pio, sm, 0, (1u << pin_sck) | (1u << pin_mosi));
-    pio_sm_set_pindirs_with_mask(pio, sm, (1u << pin_sck) | (1u << pin_mosi), (1u << pin_sck) | (1u << pin_mosi) | (1u << pin_miso));
+    pio_sm_set_pindirs_with_mask(pio, sm, 0, (1u << pin_sck) | (1u << pin_mosi) | (1u << pin_miso));
     pio_gpio_init(pio, pin_mosi);
     pio_gpio_init(pio, pin_miso);
     pio_gpio_init(pio, pin_sck);
@@ -70,6 +70,12 @@ static inline void pio_spi_init(PIO pio, uint sm, uint prog_offs, uint n_bits,
     pio_sm_init(pio, sm, prog_offs, &c);
     pio_sm_set_enabled(pio, sm, true);
 }
+
+static inline void pio_spi_enable_outputs(PIO pio, uint sm, bool output, uint pin_sck, uint pin_mosi, uint pin_miso) {
+    uint mask = output? (1u << pin_sck) | (1u << pin_mosi) : 0;
+    pio_sm_set_pindirs_with_mask(pio, sm, mask, (1u << pin_sck) | (1u << pin_mosi) | (1u << pin_miso));
+}
+
 %}
 
 ; SPI with Chip Select