rp2040 driver send still working (kinda)

1 files changed, 18 insertions, 5 deletions

diff --git a/lib/pbdrv/drv/rp2040/mod.c b/lib/pbdrv/drv/rp2040/mod.c
index 26882f7..b572c4e 100644
--- a/lib/pbdrv/drv/rp2040/mod.c
+++ b/lib/pbdrv/drv/rp2040/mod.c
@@ -11,12 +11,13 @@
 #define PBDRV_I2C i2c0
 #define BUF_SIZE 256
 
-// NOTE: this function is called from the I2C ISR, and should return as quickly
-// as possible.
+/**
+ * \note this function is called from the I2C ISR, and should return as quickly
+ * as possible.
+ */
 static void recv_event(i2c_inst_t *i2c, i2c_slave_event_t event) {
-	uint8_t data[BUF_SIZE];
-	size_t size = 0;
-	// pbdrv_i2c_recv(NULL, 0);
+	static uint8_t data[BUF_SIZE];
+	static size_t size = 0;
 
 	switch (event) {
 		case I2C_SLAVE_RECEIVE: {
@@ -39,6 +40,18 @@ void pbdrv_setup() {
 	i2c_slave_init(PBDRV_I2C, PBDRV_MOD_ADDR, &recv_event);
 }
 
+/**
+ * While the RP2040's datasheet claims it supports multi-master configurations
+ * by implementing bus arbitration, it does not natively support a mode where
+ * it is configured as a (multi-)master with a slave address, such that it can
+ * be addressed by other multi-masters. This function includes a hacky
+ * workaround that teporarily sets the RP2040 to I2C master mode to send a
+ * message, and then restores it back to slave mode.
+ *
+ * This approach results in some received frames being (partially) dropped in
+ * the time period between the invocation of this function and the bus becoming
+ * idle (and the message is sent).
+ */
 __weak void pbdrv_i2c_send(i2c_addr_t addr, const uint8_t * buf, size_t sz) {
 	i2c_set_slave_mode(PBDRV_I2C, false, PBDRV_MOD_ADDR);